U.S. patent application number 11/177094 was filed with the patent office on 2005-12-08 for combinatorial synthesis.
Invention is credited to Castellano, Christopher R., Koermer, Gerald Steven, Moini, Ahmad.
Application Number | 20050271795 11/177094 |
Document ID | / |
Family ID | 28674371 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050271795 |
Kind Code |
A1 |
Moini, Ahmad ; et
al. |
December 8, 2005 |
Combinatorial synthesis
Abstract
Methods are disclosed for providing a library of composite
compositions on a support. The method involves depositing one or
more components onto the support on either discrete spaced regions
of the support or as a continuous concentration gradients on the
surface of the support. The composite samples can be removed from
the support by drilling out portions of the coated support so as to
yield individual composite tablets containing the support with one
or more component layers thereon. By using this method, a vast
number of composites can be made and tested simultaneously.
Inventors: |
Moini, Ahmad; (Princeton,
NJ) ; Koermer, Gerald Steven; (Roseland, NJ) ;
Castellano, Christopher R.; (Ringoes, NJ) |
Correspondence
Address: |
FRENKEL & ASSOCIATES
3975 UNIVERSITY DR., STE. 330
FAIRFAX
VA
22030
US
|
Family ID: |
28674371 |
Appl. No.: |
11/177094 |
Filed: |
July 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11177094 |
Jul 8, 2005 |
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10118185 |
Apr 8, 2002 |
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6949267 |
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Current U.S.
Class: |
427/8 |
Current CPC
Class: |
B01J 2219/00612
20130101; B01J 2219/00605 20130101; B01J 2219/00754 20130101; B01J
2219/00745 20130101; Y10T 428/24479 20150115; B01J 2219/00527
20130101; B01J 2219/00722 20130101; B01J 2219/00432 20130101; C40B
40/14 20130101; B01J 2219/00585 20130101; B01J 2219/00518 20130101;
B01J 2219/0059 20130101; B01J 2219/00659 20130101; B01J 2219/0061
20130101; C40B 60/14 20130101; B01J 2219/00747 20130101; C40B 40/18
20130101; C40B 30/08 20130101; B01J 2219/00475 20130101; B01J
2219/0043 20130101; B01J 2219/00596 20130101; B01J 2219/00637
20130101; B01J 19/0046 20130101 |
Class at
Publication: |
427/008 |
International
Class: |
B05D 001/00; B22F
007/00 |
Claims
1. A method of producing a library of composite compositions on a
substrate sheet comprising: forming a plurality of different
composite compositions on said sheet, said composite compositions
comprising one or more components deposited on said substrate
sheet, at least one of said components being deposited onto said
substrate by a screen printing process and testing said composite
compositions for properties, said method of producing said library
devoid of any step which causes substantial reaction of any
deposited component with another deposited component or said
substrate sheet.
2-5. (canceled)
6. The method of claim 1, wherein said plurality of different
composite compositions are formed on said substrate sheet by
depositing one or more components to discrete, predefined regions
of said substrate sheet.
7. The method of claim 6, wherein said different composite
compositions contain a different number of deposited
components.
8. The method of claim 6, wherein said different composite
compositions contain the same deposited components but at different
deposition thicknesses on said substrate sheet.
9. The method of claim 6, wherein said different composite
compositions contain the same deposited component, but wherein said
deposited component is provided in different concentrations.
10. The method of claim 6, wherein said different composite
compositions contain a plurality of deposited component layers,
which are the same, but wherein the order of the plurality of
deposited component layers is different with respect to each
composite composition.
11. (canceled)
12. The method of claim 1, wherein said components are deposited as
a dry solid or as a solid contained within a liquid carrier onto
said substrate sheet.
13-15. (canceled)
16. The method of claim 1, wherein at least one of said deposited
components is in the form of a metal salt, elemental metal,
metallic oxide, metal oxide ceramic, non-oxide ceramic or
carbon.
17. The method of claim 1, wherein at least one of said deposited
components is a polymer.
18-21. (canceled)
22. The method of claim 1, wherein said different composite
compositions are formed by the deposition of at least one component
layer across said substrate sheet in the form of a continuous
concentration gradient of said component.
23. The method of claim 22, wherein said concentration gradient
exists along only one axis of said substrate sheet.
24. The method of claim 22, wherein said concentration gradient
exists along at least two axes of said substrate sheet.
25. The method of claim 22, wherein a plurality of component layers
are deposited onto said substrate sheet, at least one of said
plurality of component layers being in the form of a concentration
gradient across the surface of said substrate sheet.
26. The method of claim 25, wherein said different composite
compositions are formed by depositing at least one uniform
component layer across substantially the entire sheet and at least
one component layer in the form of a concentration gradient across
the surface of said substrate sheet.
27. The method of claim 22, wherein said different composite
compositions are formed by depositing at least two different
composite layers on said substrate sheet in the form of
concentration gradients across the surface of said substrate
sheet.
28-37. (canceled)
38. The method of claim 1 wherein said composite composition is a
catalyst.
39. The method of claim 1 wherein said composite composition is an
adsorbent.
40. The method of claim 1 wherein said composite composition is a
pigment.
41-69. (canceled)
70. A method of producing a library of composite catalyst
compositions on a cordierite substrate sheet comprising: forming a
plurality of different composite catalyst compositions on said
sheet, said composite catalyst compositions comprising one or more
components deposited on said substrate sheet, and testing said
composite catalyst compositions for properties, said method of
producing said library devoid of any step which causes substantial
reaction of any deposited component with another deposited
component or said substrate sheet.
71. The method of claim 70, wherein said different composite
catalyst compositions are formed by the deposition of at least one
component layer across said substrate sheet in the form of a
continuous concentration gradient of said component.
Description
FIELD OF THE INVENTION
[0001] This invention is directed to a method for preparation of
large numbers of composite materials suitable for combinatorial
screening. Depositing individual components of the composites onto
sheets using various coating techniques forms the composites.
Either numerous discrete regions on the sheet are coated with a
different composition, or large portions of the sheet are provided
with one or more coatings which form continuous concentration
gradients along one or more axes of the sheet. Composite samples
containing one or more components attached to the sheet are then
cut or otherwise removed from different regions of the coated sheet
and screened for any number of useful properties including, but not
limited to, physical, electrical, and chemical properties and any
numerous subsets of such properties.
BACKGROUND OF THE INVENTION
[0002] Combinatorial Chemistry, also known as High Throughput
Experimentation, is an emerging area that has impacted various
fields. Although still evolving, the procedure is fully established
in the pharmaceutical industry. There is increasing interest in
applying such techniques in materials science since the
combinatorial synthesis method can be a very powerful tool in
increasing the rate of experimentation, and therefore, improving
the possibility for making discoveries.
[0003] The discovery of new materials with novel chemical and
physical properties often leads to the development of new and
useful technologies. Over forty years ago, for example, the
preparation of single crystal semiconductors transformed the
electronics industry. Currently, there is a tremendous amount of
activity being carried out in the areas of superconductivity,
magnetic materials, phosphors, nonlinear optics and high strength
materials. Unfortunately, even though the chemistry of extended
solids has been extensively explored, few general principles have
emerged that allow one to predict with certainty composition,
structure and reaction pathways for the synthesis of such solid
state compounds. Importantly, it is difficult to predict a priori
the physical and chemical properties a particular composition and
structure will possess.
[0004] Clearly, the preparation of new materials with novel or
desired chemical and physical properties is at best happenstance
with our current level of understanding. Consequently, the
discovery of new materials is limited by the ability to synthesize
and analyze new compounds or compositions. As such, there exists a
need in the art for a more efficient, economical and systematic
approach for the synthesis of novel materials and for the screening
of such materials for useful properties.
[0005] One of the processes whereby nature produces molecules
having novel functions involves the generation of large collections
(libraries) of molecules and the systematic screening of those
libraries for molecules having a desired property. An example of
such a process is the humoral immune system which in a matter of
weeks sorts through some 10.sup.12 antibody molecules to find one
which specifically binds a foreign pathogen (Nisonoff, et al., The
Antibody Molecule (Academic Press, New York, 1975)). This notion of
generating and screening large libraries of molecules has recently
been applied to the drug discovery process. The discovery of new
drugs can be likened to the process of finding a key which fits a
lock of unknown structure. One solution to the problem is to simply
produce and test a large number of different keys in the hope that
one will fit the lock.
[0006] Using this logic, methods have been developed for the
synthesis and screening of large libraries up to 10.sup.14
molecules) of peptides, oligonucleotides and other small molecules.
Geysen, et al., for example, have developed a method wherein
peptide syntheses are carried out in parallel on several rods or
pins (see, J. Immun. Meth. 102:259-274 (1987), incorporated herein
by reference). Generally, the Geysen, et al. method involves
functionalizing the termini of polymeric rods and sequentially
immersing the termini in solutions of individual amino acids. In
addition to the Geysen, et al. method, techniques have recently
been introduced for synthesizing large arrays of different peptides
and other polymers on solid surfaces. Pirrung, et al. have
developed a technique for generating arrays of peptides and other
molecules using, for example, light-directed, spatially-addressable
synthesis techniques (see, U.S. Pat. No. 5,143,854 and PCT
Publication No. WO 90/15070, incorporated herein by reference. In
addition, Fodor, et al. have developed, among other things, a
method of gathering fluorescence intensity data, various
photosensitive protecting groups, masking techniques, and automated
techniques for performing light-directed, spatially-addressable
synthesis techniques (see, Fodor, et al., PCT Publication No. WO
92/10092, the teachings of which are incorporated herein by
reference).
[0007] Using these various methods, arrays containing thousands or
millions of different elements can be formed (see, U.S. Pat. No.
5,424,186, the teachings of which are incorporated herein by
reference). As a result of their relationship to semiconductor
fabrication techniques, these methods have come to be referred to
as "Very Large Scale Immobilized Polymer Synthesis," or "VLSIPS.TM.
technology. Such techniques have met with substantial success in,
for example, screening various ligands such as peptides and
oligonucleotides to determine their relative binding affinity to a
receptor such as an antibody.
[0008] U.S. Pat. No. 5,985,356, issued Nov. 16, 1999, the entire
content of which is herein incorporated by reference, discloses the
combinatorial synthesis for making and testing an array of novel
materials. This patent provides methods and apparatus for the
preparation and use of a substrate having an array of diverse
materials in predefined regions thereon. A substrate having an
array of diverse materials thereon is prepared by delivering
components of materials to predefined regions on the substrate, and
simultaneously reacting the components to form at least two
materials. Materials which can be prepared using the methods and
apparatus of the present invention include, for example, covalent
network solids, ionic solids and molecular solids. More
particularly, materials which can be prepared include inorganic
materials, intermetallic materials, metal alloys, ceramic
materials, organic materials, organometallic materials,
non-biological organic polymers, composite materials (e.g.,
inorganic composites, organic composites, or combinations thereof),
etc. Once prepared, these reaction products can be screened in
parallel or sequentially for useful properties including, for
example, electrical, thermal, mechanical, morphological, optical,
magnetic, chemical and other properties. As such, the patented
invention provides methods and apparatus for the parallel synthesis
and analysis of novel materials having new and useful
properties.
[0009] In one embodiment of U.S. Pat. No. 5,985,356, a first
component of a first material is delivered to a first region on a
substrate, and a first component of a second material is delivered
to a second region on the same substrate. Thereafter, a second
component of the first material is delivered to the first region on
the substrate, and a second component of the second material is
delivered to the second region on the substrate. The process is
optionally repeated, with additional components, to form a vast
array of components at predefined, i.e., known, locations on the
substrate. Thereafter, the components are simultaneously reacted to
form at least two materials. The components can be sequentially or
simultaneously delivered to predefined regions on the substrate in
any stoichiometry, including a gradient of stoichiometries, using
any of a number of different delivery techniques.
[0010] In another embodiment, a method is provided for forming at
least two different arrays of materials by delivering substantially
the same reaction components at substantially identical
concentrations to reaction regions on both first and second
substrates and, thereafter, subjecting the components on the first
substrate to a first set of reaction conditions and the components
on the second substrate to a second set of reaction conditions.
Using this method, the effects of the various reaction parameters
can be studied on many materials simultaneously and, in turn, such
reaction parameters can be optimized. Reaction parameters which can
be varied include, for example, reactant amounts, reactant
solvents, reaction temperatures, reaction times, the pressures at
which the reactions are carried out, the atmospheres in which the
reactions are conducted, the rates at which the reactions are
quenched, the order in which the reactants are deposited, etc.
[0011] In the delivery systems of the patented invention, a small,
precisely metered amount of each reactant component is delivered
into each reaction region. This may be accomplished using a variety
of delivery techniques, either alone or in combination with a
variety of masking techniques. For example, thin-film deposition in
combination with physical masking or photolithographic techniques
can be used to deliver various reactants to selected regions on the
substrate. Reactants can be delivered as amorphous films, epitaxial
films, or lattice and superlattice structures. Moreover, using such
techniques, reactants can be delivered to each site in a uniform
distribution, or in a gradient of stoichiometries. Alternatively,
the various reactant components can be deposited into the reaction
regions of interest from a dispenser in the form of droplets or
powder. Suitable dispensers include, for example, micropipettes,
mechanisms adapted from ink-jet printing technology, or
electrophoretic pumps.
[0012] Once the components of interest have been delivered to
predefined regions on the substrate, they are reacted using a
number of different synthetic routes to form an array of materials.
The components can be reacted using, for example, solution based
synthesis techniques, photochemical techniques, polymerization
techniques, template directed synthesis techniques, epitaxial
growth techniques, by the sol-gel process, by thermal, infrared or
microwave heating, by calcination, sintering or annealing, by
hydrothermal methods, by flux methods, by crystallization through
vaporization of solvent, etc. Thereafter, the array can be screened
for materials having useful properties.
[0013] Similar to the formation of a large array of compositions as
described in U.S. Pat. No. 5,985,356, is a technique for forming an
array of different compositions, including metal alloys wherein the
individual components that form the composition are applied by thin
film deposition as continuous concentration gradients across a
sheet. J. J. Hanak, "The `Multiple-Sample Concept` in Materials
Research: Synthesis, Compositional Analysis and Testing of Entire
Multicomponent Systems", Journal of Materials Science 5 (1970)
964-971 discusses the development of multicomponent synthesis
including the use of a technique of co-evaporating or co-sputtering
two or more elements from different, physically separated sources
onto a suitable substrate. In one experiment, almost the entire
composition continuum of a given binary or ternary system was
deposited on one substrate. Specimens made by the foregoing
techniques have to be analyzed for chemical content point by point
by existing chemical or physical methods. Thus the advantage gained
by the synthesis technique was all but lost in the analytical
methods. The article discloses that a unique computerized
analytical method was developed based on the measurement of a
simple extensive property common to all deposited films, namely,
the thickness. In order to obtain analysis for the entire
composition range the only required measurements are the two
thickness measurements for a given binary system or three such
measurements for a ternary system. The development of the
computerized analysis is stated to have meant the removal of the
main obstacle to the realization of the multiple sample concept.
Goldfarb, et al., "Novel Sample Preparation Technique for the Study
of Multiple Component Phase Diagrams", Materials Letters 21 (1994)
149-154, provides a technique for alloy sample preparation based on
thin film deposition, for a study of binary and ternary
compositions. Thin elemental wedge-shaped layers of the components
were gradually sputtered in an alternating manner to form a
multi-layered structure. The samples obtained had compositions
which depended upon the location of the substrate. Such samples,
containing differently composed Au--Ag--Cu alloys were heat treated
to promote formation of stable phases. The alloys formed were
studied by x-ray diffraction and various microscopic techniques.
The article demonstrates the advantages of the disclosed method
over conventional bulk-based methods. A similar approach was taken
to evaluate alternative thin-film dielectrics as described in
Letters to Nature, "Discovery of a Useful Thin-film Dielectric
Using a Composition-Spread Approach", R. B. van Dover, et al.,
Nature (vol. 392) 12 Mar. 1998. In this article, a wide range of
compositions were efficiently evaluated by using a technique of
depositing a single film with a ternary composition spread on a
sheet and evaluating the critical properties as a function of
position on the sheet which is directly related to material
composition using an automated tool, the continuous composition
spread technique.
[0014] Different from new materials in which new chemical compounds
are formed from reaction mixtures of distinct reaction elements or
compounds, or alloys, which are solid solutions of two or more
components, are composite materials, which typically comprise one,
or more components arranged as unreacted mixtures or layers.
Composite materials are widely used for industrial and consumer use
and are formed based upon the idea that a mixture of components can
yield a better property configuration than a single base component.
Among the numerous objects which can be formed as composites,
non-limiting samples include heterogeneous catalysts, adsorbents
for gas or liquid separations and pigments. Heterogeneous
catalysts, for example, are widely used for industrial processing
and/or in consumer goods, such as, for example, as oxidation
catalysts contained in catalytic converters of automobiles. As
opposed to new compounds from deposited reactive layers, the
chemical compositions which form the distinct deposited compounds
of heterogeneous catalysts remain mostly distinct from the other
compounds. The activity of particular catalysts, the selectivity to
achieve the desired product, thermal, hydro and hydrothermal
stabilities of the heterogenous catalysts often depend upon the
distinct layered configuration of the deposited metal, metal oxide
or other compounds as well as the distinct composition of each
layer and/or thickness of each layer which are deposited to form
the heterogeneous catalytic material. Moreover, often the
heterogenous catalyst is supported on a metallic or ceramic support
which although may be neutral with respect to the chemical
reactants contacting the catalyst, may have a physical or chemical
effect on the catalytic components in immediate contact or
approximate to the support. Thus, for catalytic converters,
cordierite honeycombs are typically coated with one or more
washcoats of catalytic layers. It is not uncommon for the
cordierite substrate to alter the catalytic properties of the layer
or layers in contact or proximate contact with the substrate such
that differences between contemplated and actual results achieved
with the catalyst may disadvantageously exist.
[0015] The present invention is not intended to be limited to
heterogeneous catalysts. Many base components are mixed with
additives to adjust a variety of physical, chemical and/or
electrical properties. Among non-limiting examples, are porous,
crystalline adsorbents, which are combined with other major or
minor phases to modify adsorption properties, improve throughputs,
provide for improved selectivity of adsorbed components, etc.
Pigment bases are provided with additives to improve color, luster,
strength, flowability, etc. Plastic composites are formed to
provide tailored physical properties, to provide thermal, UV,
moisture stabilities, improved over the base resin.
[0016] Regardless of the use of the composite, there is usually a
need to test different compositions, configurations of
compositional layers and/or relative concentrations of the
components with respect to each other. Accordingly, an enormous
problem exists with respect to testing the numerous possible
combinations of materials used to form a composite. The variables
for making a composite are still huge even if the composition of
the composite is known and selected inasmuch as the arrangement
(configuration) of layers, if used, and/or concentration of the
individual components with respect to the other components still
need to be tested for the desired properties which are sought.
SUMMARY OF THE INVENTION
[0017] The present invention is directed into the preparation of
"libraries" of composites. Large numbers of the composites can be
screened to determine the effectiveness of the individual composite
compositions.
[0018] The present invention provides methods for the preparation
and use of a substrate having multiple samples of composite
compositions provided thereon. The composite samples comprise one
or more components coated onto a substrate in discrete regions of
the substrate or in continuous concentration gradients covering
large sections of the substrate and varying in concentration along
one or more axes of the substrate. The substrate, if desired can
comprise part of the composite. Such embodiment is particularly
useful when the composite is a heterogeneous catalyst since the
carrier for the catalytic layers often affects catalytic
properties.
[0019] In accordance with this invention a substrate having a
multiple number of diverse composite compositions thereon is
prepared by delivering individual components to predefined regions
on the substrate or by application of the components as continuous
gradients thereon which vary in concentration across the substrate.
Drying, if necessary, of the components placed on the substrate can
take place simultaneously after application of each component or
subsequent to application of the final component. After deposition
of the components is complete, composite samples containing one or
more components attached to the substrate can then be removed with
or without the underlying substrate layer and screened for useful
properties. As such, the invention provides methods for the
parallel synthesis of large numbers of novel composites. Analysis
can then be done on each removed composite sample.
[0020] In one embodiment for preparation of the libraries of
composite compositions of this invention, a first component is
placed on one or more discrete predefined regions of a substrate.
Subsequently, one or more additional components having the same or
different composition as the first component are applied to
discrete regions of the substrate, which regions may be the same or
different as the predefined regions of the substrate which were
coated with the previous component. The components can be applied
as discrete coating layers which remain intact or which blend
together from a small extent to complete blending to a uniform
mixture. What is formed is multiple samples of composite
compositions placed at discrete, predefined locations on the
substrate, each discrete region comprising a different composite
composition from another with respect to either the number of
components, the composition of the components, concentration of the
components and/or thickness of the individual coating layers. If
required, the samples of discrete component compositions can be
heated to dry the deposited components such as to drive off
solvents or carriers used in the coating process. A calcination
step to convert metal salts to metal oxides or to burn off certain
organic components may also be required. Any heating step, however,
is not for the purpose of reacting one deposited layer or component
with a contiguous layer, component, or the substrate to form a
reaction product. In this invention, each coating layer or
deposited component remains substantially intact and unmodified.
Subsequent to application of the composite components and drying,
if needed, the composite samples can be removed from the substrate
or the discrete regions containing the composite samples can be
removed along with the underlying substrate as a base layer and the
individual composite samples analyzed for properties, e.g.
chemical, physical, electrical, etc.
[0021] The delivery systems used to form the composite libraries of
the present invention, deliver a small precisely metered amount of
each component or layer onto each discrete region of the substrate.
This may be accomplished using a variety of delivery techniques,
either alone or in combination with a variety of masking
techniques. For example, thin-film or thick film deposition in
combination with physical masking or photolithographic techniques
can be used to deliver various components or layers to selected
regions on the substrate. Immersion and roll-coating with physical
masking are also useful. Screen printing techniques have been found
to be unexpectedly useful in providing the multiple coating layers
in spaced and discrete region of the substrate. Moreover, using
such techniques, the composite components can be delivered to each
site in a uniform distribution, or in a variety of concentrations.
Alternatively, the various composite components can be deposited
into the discrete regions of interest from a dispenser in the form
of droplets or powder. Suitable dispensers include for example,
micropipettes, mechanisms adapted from ink-jet technology, or
electrophoretic pumps. Once the components of interest have been
delivered to the predefined regions on the substrate, the
components as a mixture or in layers, if needed, can be activated
by a number of different techniques such as heating, thermal
oxidation, thermal reduction, hydrothermal treatment so as to
convert metal salts to oxides or metal or simply to evaporate,
combust or otherwise remove solvents or carriers used to apply the
various coating layers. The composite samples are then removed such
as by being cut out of the library along with the substrate to form
individual sample "tablets". Thereafter, the tablets can be
screened for the various chemical and physical properties and the
like. Removal of the composite sample with the substrate is
particularly useful in forming multiple catalyst samples.
[0022] An alternative approach to generate libraries of composite
compositions, is a technique which generates a library of composite
samples using one or more coatings in the form of continuous
concentration gradients placed on the surface of a substrate. What
is meant by "concentration", is the amount, e.g. weight or moles,
of the component per a unit area of the substrate. By such
technique, an infinite number of point compositions are formed.
Accordingly, the potential number of composites resulting from the
formation of gradients across a substrate surface is much higher
than in the approach in which the composite samples are formed in
individual discrete regions of the substrate. In this embodiment of
the present invention in which gradients of coatings are applied
across the substrate, the loading for a particular component
increases in a uniform fashion as the coating moves across the
2-dimensional substrate sheet. The gradient can change along one or
more axes of the substrate sheet. Further, a plurality of coating
gradients can be applied across the substrate. Once a desired
composition range is defined, it is possible to generate a library
that contains all of the intermediate compositions. Samples with
any specific composition can be removed from such a library by
going to the appropriate location on the sheet. Once the uniform
gradients are applied to the substrate, it is important to be able
to calculate the composition of any specific spot of the gradient
based on its location. A mathematical protocol has been devised for
determining these compositions and is discussed in more detail
below. Methods of generating the gradient coatings include, but are
not limited to spray coating techniques, screen printing
techniques, draw down methods, gravure roll and offset press
coating techniques. The individual composite samples can be cut out
of the sheet at any desired location and, again, the individual
sample tested for physical and chemical properties and the
like.
[0023] Often, the substrate that carries catalytic layers in a
catalyst has an effect on catalytic properties. The present
invention, therefore, provides a process for producing a library of
heterogeneous catalysts in which the individual catalyst samples
that are removed contain the deposited coating layers and the base
or support. Thus, in accordance with a further embodiment of this
invention, the support upon which is applied the various composite
components such as catalytic layers, can be pre-cut or perforated
into a plurality of shapes such as circles which are dispersed on
discrete regions of the substrate. Upon application of the various
catalytic layers in the discrete regions, the catalyst layers and
underlying substrate can be readily punched out of the array into
individual catalyst tablets wherein the catalyst comprises the
various coating layers and the support. In a further embodiment,
discrete portions of the support for holding the multiple composite
samples can initially be completely cut from the base into a
variety of shapes, e.g. circles, and the cut support itself
supported during the coating operation by a second base layer
placed underneath the cut support. Upon completion of the coating
process, the underlying bottom layer can be removed and the
composite samples dropped from the remaining support. If the base
is perforated without a continuous cut, the samples can be lightly
punched or picked out from the remaining substrate. It is also
possible to use the pre-cut or perforated supports for supporting
the gradient coatings.
[0024] Other objects and advantages of the present invention can be
readily ascertained from the description of the invention which
follows as well as from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIGS. 1 and 1A represent the use of a mask to apply a
composite component onto discrete regions of a support.
[0026] FIGS. 2(A-H) represent the use of three different masks to
form an 8.times.8 grid of discrete regions on a support wherein
each of the 64 discrete regions on the support has a different
composite composition as shown in the side views of FIG. 2 H.
[0027] FIGS. 3A and 3B represent, respectively, the removal of the
composite samples by coring from the support after coating and the
individual composite "tablets" which are formed and which can be
sampled for properties.
[0028] FIG. 4 represents a plot illustrating the application of a
component coating layer in a concentration gradient, wherein the
component loading changes only along the x-axis of the support.
[0029] FIG. 5 also represents a plot showing the application of a
component coating layer in a concentration gradient across the
support, wherein the minimum component loading occurs at a corner
of the support and increases as a function along both the x and y
axes of the support.
[0030] FIG. 6 represents one embodiment of the process of this
invention wherein the coating layers are applied to rolled and
pre-cut sheets and the coated samples removed from the cut portions
of the sheet.
[0031] FIGS. 7A-7F represent typical configurations of composites
using multi-layered gradient component coatings, wherein arrows A
and B represent increases in the component concentration and x, y
represent the coordinates of the desired composite samples, the
composition of which can be determined by the equation depicted for
each figure as set forth below.
[0032] FIG. 8 is a photograph of a Pt/alumina coating on cordierite
in the form of a continuous concentration gradient as depicted in
FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0033] In one embodiment of the present invention, a method is
provided for the preparation of multiple samples of composite
compositions provided on a plurality of spaced, predefined regions
of a support. In a preferred embodiment, the substrate becomes part
of the composite.
[0034] This is useful in testing heterogeneous catalyst samples,
for example, since often the substrate, which carries the active
catalytic layers, has an effect on catalytic properties.
Heterogeneous catalysts including the substrate are provided as
individual catalyst samples which can be individually tested for
catalytic properties as well as other chemical, physical, and
electrical properties. The heterogeneous catalyst samples are
provided by coating one or more catalytic layers onto the substrate
in spaced, predefined regions whereby one region will have an
overall catalyst composition comprising one or more layers of
catalytic material which is different from the catalyst composition
contained on other predefined regions of the substrate. The
catalyst samples can be cut out from the discrete regions of the
support as tablets and the individual catalytic tablets tested for
desired properties.
[0035] The library of composites is not intended to be limited to
forming samples of heterogeneous catalysts. The composite samples
which are formed can be for any and all useful purposes. Additional
non-limiting examples include catalysts, adsorbents, pigments,
coatings, ceramics, glasses, sensors, electronic materials, optical
materials, construction materials, molded plastic parts, etc.
[0036] Flat sheets made from a variety of materials can serve as a
substrate for forming the library of composite components in the
methods of this invention. Thus, the sheets can be made of
ceramics, such as oxides or silicates, including, for example,
alumina, zirconia, etc., and cordierite; non-oxide ceramics such as
metal carbides and nitrides; metals, such as, for example,
stainless steel, aluminum, etc.; glass; polymers; and composites of
the listed materials. Porous as well as dense materials can be
utilized. It is most useful if the substrate, whether rigid or
semi-rigid, can be cut or perforated so as to yield individual
sample tablets subsequent to the coating process and which can be
tested for properties as described above. It is preferred that the
substrate used be one that is compatible with the components or
layers that are delivered to the substrate and can be used
effectively in the environment in which the composite is to be
used. For example, cordierite sheets are especially preferred as a
substrate for heterogeneous catalysts since cordierite is known as
a support for catalytic layers such as in automotive catalytic
converters. Thus, cordierite sheets provided with multiple samples
of various catalytic layers can mimic honeycomb monoliths, which
are used in automotive catalytic converters.
[0037] The composite components which are applied to discrete,
predefined regions of the substrate are typically metals and metal
oxides which can be coated onto the substrate in the form of a
solid, liquid, slurry or solution, including inks, pastes, gels,
suspensions, or vapor phase. The component can be deposited onto
the substrate by various coating techniques such as spraying,
immersion, pouring, rolling, vapor deposition techniques, etc.
Aforementioned U.S. Pat. No. 5,985,356 discloses numerous
techniques for applying reactive components to form a combinatorial
array. Such techniques can be readily used herein to form a library
of composite compositions.
[0038] The types of materials that can be applied as coatings
include but are not limited to:
[0039] (a) Oxides of metals and main group elements, including
transition metal oxides such as zirconia, titania, manganese oxide,
rare earth oxides such as ceria and lanthanum oxide; binary,
ternary, and more complex solid state oxides and ceramic phases;
various forms of alumina, silica, aluminosilicates and
aluminophosphates.
[0040] (b) Natural and synthetic forms of aluminosilicate and
silicate zeolites such as ZSM-5, Beta, zeolite Y, and ferrierite,
various forms of molecular sieves such as aluminophosphates and
titanosilicates; natural or synthetic clays and related minerals
such as kaolin, attapulgite, talc, montmorillonite, and
Laponite.RTM..
[0041] (c) Non-oxide ceramics such as metal carbides and
nitrides.
[0042] (d) Various forms of carbons such as activated carbon,
carbon molecular sieves, graphite, fullerenes, carbon nanotubes,
and carbon black.
[0043] (e) Various organic polymers, oligomers, or resins, such as
polyethylene, polypropylene, polystyrene, polyamides, halo
hydrocarbon polymers, polyesters, etc.
[0044] (f) Metals such as precious metals and/or transition metals
deposited, mixed with, or exchanged into any support such as any of
the materials described in (a)-(e) above. Examples of such phases
include Pt/alumina, Pd/alumina, and Cu-ZSM-5.
[0045] The metals or metal oxides may also be initially applied as
metal salts which can be reduced or oxidized to the desired metal
or metal oxide layer. The types of metals, metal compounds or
non-metallic components that can be applied are limited only to the
extent of the periodic table of elements and accordingly, there are
no further limitations as to the elements, compounds or polymers
that can be used as components. It is this availability of vast
numbers of materials and the indefinite combinations of the
materials that can be prepared, especially when more than one
composite component or layer is applied, that leads to the
necessity and importance of finding a way of preparing and testing
a vast library of composite samples.
[0046] One very useful way of applying one or more composite
components or layers on a predefined area of a substrate is shown
in FIG. 1. As depicted therein, a flat substrate 10 is to be
provided with a composite component layer which can be applied in
the form of a fluid composition 12 which can be a solution or
dispersion having a low viscosity such as an ink or higher
viscosity such as a gel or paste, or even as a gas. Fluid 12
contains the component to be deposited such as, for example a metal
or metal oxide. It my be useful to premix two or more components
and apply the mixture as a component layer. If a liquid carrier is
used, either water or organic solvents or mixtures thereof are
appropriate. To ensure that the component is provided on the
desired regions of the substrate, a mask 14 containing a plurality
of openings as exemplified by openings 16 is placed so as to
overlay the substrate 10. Upon application of the fluid composition
12, the removal of excess and the removal of mask 14 from the
surface of substrate 10, the component is provided as a coating on
the discrete regions on the substrate corresponding to openings 16
of mask 14. This is shown in FIG. 1A wherein component layers 17,
18, 19, and 20 are coated onto substrate 10 corresponding to the
openings 16 of mask 14.
[0047] In order to provide the desired plurality of composite
compositions on the substrate, a series of masks can be utilized,
each mask overlaying the substrate or coated substrate prior to the
application of the next layer. FIGS. 2A-2G illustrate the
application of six component layers, some of which may be the same,
to form an 8.times.8 grid of 64 predefined regions on the substrate
which generate all of the possible combinations of a 6-variable
system. As shown in FIGS. 2(A-G), by using three masks and, using
each mask in two different orientations, six different components
can be deposited onto the surface to result in the 8.times.8 grid.
Initially, as shown in FIG. 2A, an uncoated substrate 22 is
overlaid with a mask 24 containing one opening 26. Subsequent to
the application of a coating layer (not shown) and drying (if
necessary) of the layer, mask 24 is turned 90.degree. and overlaid
onto once coated substrate 25 whereupon a second layer can then be
applied, FIG. 2B. FIGS. 2C and 2D represent the use of a mask 28
which contains two openings 30 and 31 which are again overlaid onto
previously coated substrates 32 and 33 for application of layers
three and four. As can be seen in FIG. 2C, the openings 30 and 31
are orientated perpendicular to opening 26 in FIG. 2B. Similarly,
as shown in FIG. 2D, mask 28 is oriented or turned 90.degree. from
the orientation of mask 28 in FIG. 2C such that openings 30 and 31
are perpendicular to the direction of openings 30 and 31 in FIG. 2C
prior to the application of an additional coating layer. FIGS. 2E
and 2F represent the application of coating layers five and six
wherein a mask 34 containing four openings 35, 36, 37 and 38
overlays substrate 40 which already contains four coating layers.
In FIG. 2E, the mask 34 is oriented such that the openings 35-38
are now in a direction perpendicular to the direction of openings
30 and 31 as used during the application of the component layer in
FIG. 2D. Subsequent to coating in FIG. 2E, mask 34 is now placed on
substrate 42 which has been coated five times. The final sixth coat
is applied through openings 35-38 of mask 34 in FIG. 2F where again
the mask is turned 90.degree. from the orientation used in FIG. 2E.
What results is shown in FIGS. 2G and 2H in which substrate 44
which has been coated six times contains a grid of 64 different
composite compositions. The composite sample in the upper left
corner 46 will contain all six coatings while the sample in the
lower right corner 48 will contain the substrate only without any
coating layers. All other combinations of the six coatings would
appear in the remaining samples. FIG. 2H illustrates the 64
different samples which are formed by the process depicted in FIGS.
2A-2F. While FIG. 2H illustrates the component deposits as distinct
layers it is within the scope of this invention that the deposited
component layers can blend with any contiguous layer from a state
of partial blending to a state of uniform mixture. It is important,
however, that the deposited components remain as mixtures if
blending does occur or is desired, and not as a reaction product
between two or more deposited components.
[0048] Obviously, other masking configurations can be used to form
the multiple composite compositions on the support. FIGS. 2A-2H
represent one possibility of mask use and is not intended to limit
the present invention. In the above described 6-variable example,
as shown in FIGS. 2A-2H, each catalyst coating is of a unique
composition. It is important to point out that parameters other
than coating composition can serve as a variable. For example, some
compositional libraries may contain fewer number of unique
compositions but have variations in the thickness of a coating
component. The simplest way to handle such a variation is to use
the same coating with two subsequent masks, thus providing a larger
amount of the coating to some of the predefined regions.
Alternatively, by using other mask designs, it is possible to treat
each quadrant of an the substrate as separate libraries, i.e.
prepare four 16-member libraries. The latter approach allows for
the preparation of the same number of unique samples on the ceramic
sheets, but work with fewer numbers of variables for each library.
Further, the amount of coating, deposited in solid or liquid form,
need not be uniform across the substrate or even across a specific
region of the substrate. An intentional gradient could be
introduced as one moves from one side of the substrate to the
other. The result is a step-wise concentration gradient across the
substrate from one discrete region to the next. In addition to the
method described with respect to FIGS. 2A-F, alternative approaches
can be used to deliver the various coatings on the flat substrate.
Such delivery methods are discussed above in the "Summary of the
Invention" and in aforementioned U.S. Pat. No. 5,985,356. For
example, in the process described above, in which a plurality of
physical masks are used to conform the coatings to predefined
regions on the substrate, the coatings can be applied as a fluid
such as by spraying, immersion, pipetting, or roll coating. In
addition, electrophoretic and vapor deposition methods can be used
with physical masking as shown in FIG. 2. Screen printing
techniques are very useful methods of coating specific regions of
the substrate with the composite components or layers. In screen
printing, a design or surface pattern coating is produced on a
substrate by forcing ink through a fabric mesh screen that has been
partly blocked out or masked to reveal only the pattern to be
applied. The ink is moved across the imaged screen by a squeegee.
Hydraulic pressure created by the leading edge of the squeegee
forces ink through the unblocked or unmasked portions of the screen
onto the substrate below. The variables in the screen-printing
process are numerous and can be optimized for print definition,
reproducibility, and deposition uniformity. Almost any component
material can be deposited by screen printing, and as well, any
substrate material can be screen printed, including paper, metal,
plastics, ceramics, and glass.
[0049] If metals are to be applied to the substrate, deposition can
be achieved from vapor deposition, powder or slurry of metal or
metal oxides, supported metal or metal oxides, as well as the
applications of metal salts dissolved in water or other solvent or
metal salts impregnated onto carrier particles. The metal salts can
be converted to metals or metal oxides by a subsequent reduction or
oxidation step after application of the solution, or upon
deposition of the metal salt/carrier particles and removal of the
solvent or slurry mediums. A particular useful method of applying
metals is to first impregnate or otherwise deposit a metal or metal
salt on a porous carrier particle such as alumina. The
metal/alumina particles can then be applied on predefined regions
of the substrate or as continuous gradients. Pt/alumina or
Pd/alumina are non-limiting examples of metal/carrier components.
If the alumina carrier or other porous carrier is impregnated with
metal salts, the metal salt/carrier coatings can then be treated
subsequent to deposition to oxidize or reduce the various metal
salts to metal oxides or metals, respectively. Treatment can be
immediately after each layer is applied or after all layers of
metal salts have been applied.
[0050] In the process of driving off solvents or liquid carriers
and/or converting the metal salts to metals or metal oxides by
thermal treatment, it is important that such heat treatment is not
so severe as to cause a substantial reaction between the individual
metal components or layers with other components or layers. Thus,
while two metals or metal salts may be applied, subsequent heat
treatment should still yield two different metal compounds whether
as pure metal or metal oxides. Substantial reaction between two
metal components or oxides to form a third different metal, metal
alloy, or oxide component is to be avoided. Thus, in accordance
with this invention, any treatment of the coated substrate should
not yield a substantial reaction between deposited composite
components. What is meant by not yielding a substantial reaction is
that at least 80% wt. of the deposited layers or components should
remain unreacted with any other deposited component or layer.
Preferably, at least 90% of the deposited components or layers
remain unreacted with other layers, and most preferably, greater
than 95 weight percent of the deposited layers should remain
unreacted with other deposited components or layers.
[0051] An important exception to the discussion immediately above
with respect to forming composites and not new reacted compounds
from two or more applied components is when the deposited sample is
cut from the substrate sheet along with the underlying substrate.
Thus, in this embodiment of the invention, the individual
components are deposited on the substrate sheet in either
predefined discrete areas or as continuous concentration gradients,
but with the exception that the deposited components can react with
each other or the substrate to form new compounds. For example, a
variety of aluminosilicate zeolites and the like can be formed
directly on a carrier substrate surface such as alumina,
silica-alumina, cordierite, etc. Once the new compounds are formed
on the substrate surface, the new compounds along with the
underlying carrier substrate can be removed by cutting, coring or
the like, which is specifically described below. This embodiment
allows the testing of a library of compounds, which are most useful
when contained on a support. While the uses of such compounds are
unlimited, specific examples include catalysts, adsorbents, and
pigments.
[0052] Once coated, the flat substrate can be heat treated as
described above so as to remove liquid carriers, solvents, to
convert metal salts, temper and the like. Once heat treatment is
completed, the substrate should contain discrete regions each of
which contains one or more deposited coating layers or composite
compositions wherein each composition is different from other
compositions in different predefined regions of the substrate. At
this point, the composite samples can be cut out of the library so
that the individual composition can be tested. As shown in FIG. 3A,
an 8.times.8 array such as that formed in FIG. 2G and containing a
substrate 44 and sixty-four separate composite samples, such as
sample 50 are cut out of the predefined grid region. While FIG. 3A
shows that the composite sample that is cut out is circular, in
principle, any shape is possible, for example, square, rectangle,
triangle, etc. Once the composite samples 50 are cut out from the
coated substrate 44, the individual samples 50 as shown in FIG. 3B
can then be tested for a variety of properties. It should be
understood that the composite samples can be removed with or
without the underlying substrate for testing, or tested while the
samples remain intact on the substrate. Cutting the samples such as
by coring out the samples and the underlying substrate is very
useful in testing for desired properties. Further, more than one
sample with the same composition can be removed by the cutting or
coring procedure.
[0053] Evaluation of the composite samples may consist of any type
of electronic, optical, physical, or chemical testing. For
heterogeneous catalysts this involves contacting the sample with
one or more reactive compounds at certain conditions (e.g. flow
rate, concentration, temperature, contact time, etc.) and
evaluating the extent and nature of the reactivity of one or more
of the reactive compounds by techniques such as mass spectrometry,
infra-red spectrometry, gas chromatography or any other suitable
and useful method. Typically, properties of the catalyst such as
activity, selectivity, stability, rate constants, activation
energies etc. may be determined.
[0054] The substrate that is preferably used in the above method is
flat, but may take on a variety of alternative surface
configurations. Regardless of the configuration of the substrate
surface, it is important that the components deposited in the
individual predefined regions of the substrate be prevented from
moving to adjacent regions. Most simply, this can be ensured by
leaving a sufficient amount of space between the regions on the
substrate so that the various components cannot interdiffuse
between regions. Moreover, this can be ensured by providing an
appropriate barrier between the various regions on the substrate. A
mechanical device or physical structure can be used to define the
various regions on the substrate. For example, a wall or other
physical barrier can be used to prevent the components in the
individual regions from moving to adjacent regions. Alternatively,
a dimple or other recess can be used to prevent the components in
the individual regions from moving to adjacent regions.
[0055] Instead of forming multiple samples of different composites
on a continuous substrate sheet, several smaller substrate sections
can be formed to test processing conditions on identical
compositions. The size and number of these sheets can vary
significantly depending on the particular experiment. In the case
of the ceramic substrate sheet, these smaller sections can be
easily cut from running lengths of tape cast ceramic, which
comprises ceramic particles mixed within an organic binder. Once
cut, the tape cast sheet can be fired to remove binder and provide
additional sintering of the ceramic particles. Ideally, these
sections are placed in a special platform, allowing each piece to
be firmly held in place. The entire surface, corresponding to all
of these pieces, will then be coated with the same ingredient(s).
Once coated, these identical pieces are removed and treated under
various conditions. The result is the same coating exposed to a
variety of conditions. For example, the samples could be placed in
a heating device that has a specific gradient in temperature as a
function of location. A simple approach for achieving this thermal
gradient is by placing each piece at specific regions inside a tube
furnace. Upon heating these pieces, the final array would represent
the entire range of thermal treatments. Other types of conditioning
environments can be applied to obtain this type of combinatorial
effect. In regards to different temperature treatments, it may also
be possible to treat the larger sheet containing the entire library
in a device that provides local heat to specific regions, for
example using lasers.
[0056] In the embodiment described above, the library of composite
compositions, which is formed, will comprise a finite number of
composite samples which can be deposited on the substrate sheet.
While vast numbers of composites can be deposited, the individual
composite sample must be large enough to be effectively tested for
properties, thus limiting the number of samples which can be formed
on a substrate sheet. Further, while a step-wise gradient of
concentration or compositional changes can be made across each of
the predefined regions of the sheet, a vast continuum between a
desired concentration range is not readily achieved. Accordingly,
in an alternative embodiment to providing the library of composite
compositions as coatings on discrete, predefined and spaced regions
of the substrate is to form one or more of the component coatings
as a continuous gradient across the whole of the substrate. The
gradient can be with respect to concentration or loading of a
particular component or may vary in compositional differences. By
applying a coating gradient across the substrate, it is possible to
generate a composite library that contains all of the intermediate
compositions or concentrations between a desired compositional or
concentration range. Samples with any specific composition within
the desired range can be tested from such a library by going to a
specific location on the substrate sheet and testing at such
location or cutting out the sample from the coated sheet. Thus,
libraries of composite compositions with an exhaustive range of
compositions can be prepared for one-component as well as
multi-component compositions. Several overlapping gradients can be
prepared to mimic complex multi-dimensional phase diagrams.
[0057] This embodiment of the invention where continuous gradients
of coatings are applied across the substrate are shown in FIGS. 4
and 5 where the loading for a particular composite component
increases, in a continuous fashion as the gradient moves across a
two-dimensional sheet. The plots in FIGS. 4 and 5 show two possible
configurations of useful gradient coatings. In the first
configuration shown in FIG. 4, the loading of a deposited component
is increased as the gradient moves across the x-axis of the
substrate sheet. In this case the loading changes only along the
x-axis. In the second configuration shown in FIG. 5, the minimum
loading occurs at the corner of the sheet and increase as a
function of both x and y. The coatings with continuous gradient
concentrations can be prepared as either single-component or
multi-component systems. Examples of libraries with these gradient
coatings include the following: (1) Uniform coatings of one or more
components can first be placed on the substrate sheet. In such case
the composition of the entire surface would be the same. Subsequent
to the application of the uniform coating, one or more gradient
coatings such as those described above and with respect to FIGS. 4
and 5 could be placed on top of the base coat. (2) The
configuration of FIGS. 4 and 5 may be prepared as a
single-component system to examine the effect of concentration of a
particular component on a composite. Such a technique is even more
powerful when two different gradients are placed on the same
surface. The minimum loading for the first component can be at one
corner of the sheet while the minimum loading for the second
component may be at either a neighboring corner or at the opposite
corner of the sheet to create different combinations of the two
components. Alternatively, the patterns for the two components may
overlap one another, i.e. the minimum for both would occur at the
same corner. (3) The configuration of FIG. 4 can also be used to
place two different gradient coatings. Three unique orientations of
the second gradient relative to the first are possible: (a) the
minimum loading of the second component occurs at the same location
as the minimum of the first component, therefore as the gradients
move across the sheet, loading for both components increase, (b)
the minimum loading for the second component occurs at an edge that
is adjacent to the edge for the minimum loading for the first
component. Therefore, the two patterns are 90.degree. off relative
to each other. (c) The minimum loading for the second component
occurs at an edge that is opposite of the edge of the minimum
loading for the first component, and therefore, the two patterns
are 180.degree. off relative to each other. While the libraries are
not limited in terms of the numbers of components that can be
applied, the gradient technique is quite powerful to yield a vast
number of composite compositions even when using only one or two
deposited components. The configuration as above described are just
a few of the possible ones which can be applied. The present
invention is not intended to be limited to the specific patterns
described. One of ordinary skill in the art could readily conceive
of alternate configurations for applying one or more gradient
coatings.
[0058] Delivery of the components as continuous gradients across
the surface of the substrate can be achieved by several methods.
One useful method is a spray-coating process. A spray gun is
oriented at an angle relative to the target and at one end of the
target, thus resulting in higher coating loadings at locations
closer to the spray gun and decreasing loadings with increasing
distance. An additional approach takes advantage of a fine mesh
screen that is placed between the spray gun and the target. Some of
the coating remains on the screen and thus, does not reach the
target creating the concentration gradients. By placing the screen
at an angle relative to the gun, varying amounts of the coating are
blocked by the screen depending on location and a gradient loading
is generated on the target. Relative movement and varying the speed
of the movement between the spray gun and target may be achieved
using a variable speed motor to deliver gradient coatings.
[0059] The use of screen printing is a particularly useful
technique to form gradient coatings. The appropriate screen to
deliver a gradient coating can be produced by photolithographic
techniques known in the art. FIG. 8 is a photograph of a Pt/alumina
coating on a cordierite substrate coated by a screen printing
process to apply a gradient of Pt/alumina along the x-axis of the
cordierite substrate. The movement of a draw-down bar across a
surface to vary the coating thickness, and gravure roll coating are
additional methods that can be used to form coating gradients
across the substrate surface.
[0060] Once the gradient coatings have been applied to the
substrate in the desired manner, it is important to be able to
calculate the composition of any given spot on the gradient based
on its location. A mathematical protocol has been devised for
determining these compositions depending upon the coating gradient
protocol which has been used. Representative calculations appear
below in conjunction with FIGS. 7(A-F).
[0061] In all of the following calculations, minimum loading for
each component occurs at a corner or edge of the square sheet, and
increases at a constant rate along one of the axes or the diagonal.
The value for the minimum and maximum loadings for each component
are required at the onset. The following equations show six
scenarios and the corresponding equations to determine the final
composition.
DEFINITIONS
[0062] Composition (x,y) means the composition at location x,y on
the substrate sheet. Its actual value would correspond to the total
loading at location x,y.
[0063] A.sub.min, B.sub.min, . . . minimum loading for component A,
B, etc.
[0064] A.sub.max, B.sub.max, . . . Maximum loading for components
A, B, etc.
[0065] X.sub.max, Y.sub.max Length of the x or y axes.
[0066] FIG. 7A: corresponds to two gradient coatings A and B which
have a minimum loadings at adjacent edges of the substrate sheet
and wherein the respective loadings increase from the edge along
either the x or y axis, respectively, and away from a common corner
of the sheet. 1 Composition ( x , y ) = [ A min + ( ( A max - A min
) x x max ) ] + [ B min + ( ( B max - B min ) y y max ) ]
[0067] FIG. 7B: corresponds to two gradient coatings A and B which
have a minimum loadings on adjacent edges of the substrate sheet
and wherein the loadings increase from the respective edges along
either the x and y axis respectively. 2 Composition ( x , y ) = [ A
min + ( ( A max - A min ) x x max ) ] + [ B max - ( ( B max - B min
) y y max ) ]
[0068] FIG. 7C: corresponds to two gradient coatings that have
minimum loadings on opposite edges of the substrate sheet and
wherein the prospective loadings increase in opposite directions
along one axis of the sheet. 3 Composition ( x , y ) = [ A min + (
( A max - A min ) x x max ) ] + [ B max - ( ( B max - B min ) x x
max ) ]
[0069] FIG. 7D: corresponds to two gradient coatings which have
minimum loadings along the same edge of the substrate sheet and
wherein the loadings A and B increases from such edge along one
axis along the sheet. 4 Composition ( x , y ) = [ A min + ( ( A max
- A min ) x x max ) ] + [ B min + ( ( B max - B min ) x x max )
]
[0070] FIG. 7E: corresponds to three gradient coatings A, B and C
wherein the minimum loadings for coating A and B are at adjacent
edges of the sheet and wherein the loadings increase in the
direction of the arrows along one axis of the sheet for each
coating. The third coating C has a minimum loading at the corner
between the adjacent edges and has a loading increase along
diagonal between the x and y axes. 5 Composition ( x , y ) = [ A
min + ( ( A max - A min ) x x max ) ] + [ B min + ( ( B max - B min
) y y max ) ] + [ C min + ( ( C max - C min ) ( 2 ( x + y 2 ) 2 x
max 2 + y max 2 ) ) ]
[0071] It should be noted that the scenarios listed above are
provided only as examples, and there are additional configurations
for creating multi-component gradient coatings. For example, in all
of the examples shown, it is possible to have one or more
additional components that are coated at a uniform loading
throughout the sheet.
[0072] FIG. 7F: corresponds to gradient coatings A and B as in FIG.
7A and a uniform coating C. 6 Composition ( x , y ) = [ A min + ( (
A max - A min ) x x max ) ] + [ B min + ( ( B max - B min ) y y max
) ] + C max C max = C min
[0073] FIG. 6 represents a method of forming the libraries of
composites of this invention, by either embodiment, that being by
either the application of the coating layers on predefined discrete
regions of the substrate or by utilizing one or more gradient
coatings across the surface of the substrate. Referring to FIG. 6,
a roll 70 of tape cast ceramic such as cordierite can be provided
perforations 71 by any known manner to divide roll 70 into a
plurality of individual substrate sheets 73. A tape cast ceramic
contains a ceramic phase and a binder, such as a polymer or other
binder source. The binder is burned off upon firing to provide the
pure ceramic sheet. The sheets 73 are eventually cut along the
perforations into separate substrate sheets 72 and 74. Prior to
heat treatment, the tape cast ceramic sheets are relatively soft
and are able to be cut or perforated by a sharp device. In FIG. 6,
the cut sheets, 72 and 74 are stacked one on top of the other and
while still containing binder, a sharp device can be pressed into
the sheet, e.g. a cylindrical tube with a sharp edge would result
in a perforated circle as indicated by reference numeral 76. A
plurality of these perforations 76 can be formed throughout the
surface of the substrate sheet 72. The substrate sheet 74 acts as a
base layer so as to hold the perforated sections 76 in place within
substrate sheet 72 prior to and during the coating process. Once
the tape cast sheet is perforated, the sheet is fired to remove the
binder, harden and densify the substrate sheet 72. Subsequent to
firing, one or more coating layers can be applied to the top
surface of substrate 72 by the methods described above. Thus,
discrete regions of the substrate sheet 72 can be coated with one
or more coatings or the whole surface of substrate sheet 72 can be
coated with one or more gradient coatings. The coatings are
represented by reference numeral 78 in FIG. 6. After coating, any
solvents or carriers for the coatings can be removed as by heating.
Further, any metal salts can be converted to their respective
metals or metal oxides by a thermal process and such final coating
is designated as reference numeral 80 in FIG. 6. Once the coatings
are dried and converted to the desired phases, precut samples
containing the base 72 and coating 80 can be removed as samples 82.
Various cutting devices can be used to pre-cut the desired sample
shapes in the tape cast substrate 72. Thus, instead of a
sharp-edged tube as described above, a variety of templates can be
used to make various perforated images onto sheet 72. Further
still, the base sheet 74 which acts to hold the pre-cut samples in
place in sheet 72 may be of the same material or a different
material such as a different ceramic, metal, or even plastic layer.
The purpose of the base 74 is to ensure that the pre-cut spaces
remain in place during the coating process.
EXAMPLES
General
[0074] For the following examples, ceramic sheets obtained from
Mistler (Morrisville, Pa.), were made from a cordierite powder
mixed with a binder and tape-cast into a 61/2" voll with a
thickness of 0.047". These squares subsequently require a heating
procedure to both remove the binder and provide rigidity to the
piece. The cordierite sheets were placed onto a flat surface
lightly dusted with powdered cordierite, and placed into a furnace
with the following profile: room temperature to 932.degree. F. over
1-6 hours, hold for 1/2 hour, ramp to 2100-2300.degree. F. over 1-7
hours, hold for 0.5-12 hours, then cool slowly to room temperature.
Longer heating times than those listed here are generally
acceptable.
[0075] Examples of other tapes useful for this application are a
100% alumina tape and a 96% alumina/4% glass (magnesium aluminum
silicate). An alumina marketed under Alcoa A-16SG is useful. The
alumina tapes have a similar thickness to the cordierite tapes. The
96% alumina tapes range in thickness from 0.047" to 0.050". The
100% alumina tape requires a higher temperature, e.g.
2250-2650.degree. F.
[0076] A screen printing ink is defined as a specific formulation
consisting of a powder (in this case, a catalyst or other type of
active material), a carrier solution, and a few additives that
result in a product with high-quality screen-printing properties. A
carrier is defined as a suspending agent for the solid component of
a screen printable ink. The carrier typically makes up the bulk of
the key properties of an ink and generally defines the viscosity
and tackiness. The key properties of an ink formulation are the
viscosity, and the solids loading. In order to form a good coating,
inks are required to have a high viscosity, similar for example to
a thick honey. If the viscosity is too high, the ink will not
distribute itself across the screen properly for an even and
well-distributed print. Likewise, if the viscosity of the ink is
too low, the print quality also suffers since the ink will not
distribute itself properly across the screen during the printing
and may result in smearing of the desired pattern.
[0077] Typical particle sizes of the starting powder range from 2
.mu.m to 50 .mu.m. The ink goes through a blending and milling
process, which reduces the particle size down to 1-25 .mu.m.
Typically screens are made of polyester or stainless steel
monofilaments woven into a grid pattern. Monofilament diameters
range from 0.6 mils (or 15 .mu.m) up to 15.2 mils (or 385 .mu.m).
Typical square openings formed by the monofilaments measured as one
side of the square, range from about 1.1 mils (or 26 .mu.m) up to
10.5 mils (or about 266.7 .mu.m). Patterns on the screen printer
can typically range from 5 mils up to 10" across.
Examples 1-16
[0078] A standard carrier used in the following experiments had the
following formulation:
[0079] 1.1 wt % N100 Ethyl Ether Cellulose (Hercules-Aqualon N100
grade) dissolved overnight in a 1:1 mixture of a-Terpineol
(Aldrich) and Texanol (American Chemicals).
[0080] The following formulations are examples only. The possible
variations are not limited to this list. Also prepared and used
were other carriers with the following formulations. These
variations were used to change the viscosity and solids loading of
the final inks.
[0081] (1) 1.1 wt % N50 Ethyl Ether Cellulose (Hercules-Aqualon N50
grade) dissolved in a 1:1 mixture of a-Terpineol (Aldrich) and
Texanol (American Chemicals)
[0082] (2) 1.1 wt % N300 Ethyl Ether Cellulose (Hercules-Aqualon
N300 grade) dissolved in a 1:1 mixture of a-Terpineol (Aldrich) and
Texanol (American Chemicals)
[0083] (3) 0.55 wt % N100 Ethyl Ether Cellulose (Hercules-Aqualon
N100 grade) dissolved in a 1:1 mixture of a-Terpineol (Aldrich) and
Texanol (American Chemicals)
[0084] (4) 1.65 wt % N100 Ethyl Ether Cellulose (Hercules-Aqualon
N100 grade) dissolved in a 1:1 mixture of a-Terpineol (Aldrich) and
Texanol (American Chemicals)
[0085] (5) 2.5% wt % XLO-VP (Ethyl cellulose) in deionized
water.
[0086] The compositional details of the various experimental inks
that were prepared are listed in Table 1. A detailed description of
a typical preparation (Example 6) is listed below.
[0087] First, 30.0 mL of a-terpineol (Aldrich) was measured out
into a graduated cylinder, to which 30.0 mL of Texanol (American
Chemical) was added. The mixture was the placed into a beaker with
a magnetic stir-bar and allowed to stir for 5 minutes. Then, 1.10
wt % of Ethyl Ether Cellulose (Hercules-Aqualon N100 grade) was
measured out and added to the a-Terpineol/Texanol mixture, which
was allowed to stir covered overnight. Next, 20.0 grams of alumina
(SBA-150) powder was weighed out into a mixing bowl to which 18.0
grams of the above solution was added. Finally, 0.80 gram of
Sarkosyl-O (CIBA) and 3.0 grams of a-Terpineol were added, and the
whole mixture was blended thoroughly with a spatula and processed
in a Ross 2.5.times.5 three-roll mill.
[0088] This blended ink was used in a screen printer to produce a
coating onto a cordierite sheet. It was then dried at 100.degree.
C. for 15 minutes, followed by calcinations at 540.degree. C. for 2
hours. The resulting product is a coating of alumina on the surface
of the ceramic sheet.
1TABLE 1 Examples of ink compositions grams of ingredient added
Material/ Carrier Material/ Example Catalyst type.sup.a catalyst
Carrier Sarkosyl-O a-Terpineol 1 3% 1.1% N100 14.0 11.0 0.80 0.40
Pt/Al2O3 2 3% 1.1% N100 10.0 10.5 0.50 1.00 Cu/ZSM-5 3 ZSM-5 1.1%
N100 10.0 9.3 0.20 1.00 4 ZSM-5 1.1% N100 4.0 3.7 0.08 0.40 5 ZSM-5
2.5% XLO- 4.0 4.5 VP 6 Al2O3 1.1% N100 20.0 18.0 0.80 3.00 7 Al2O3
1.1% N100 60.0 54.0 2.40 9.00 8 CeO2 1.1% N100 32.0 18.0 1.00 3.00
9 CeO2 1.1% N100 96.0 54.0 3.00 5.00 10 CeO2 1.1% N50 32.0 18.0
1.00 1.60 11 CeO2 1.1% N300 32.0 18.0 1.00 1.60 12 CeO2 0.55% N100
32.0 18.0 1.00 1.60 13 CeO2 1.65% N100 32.0 18.0 1.00 1.60 14 TiO2
1.1% N100 30.0 35.0 3.50 0.00 15 Na2CO3 1.1% N100 50.0 30.0 2.00
0.00 16 K2CO3 1.1% N100 50.0 24.0 1.50 0.00 .sup.aAs described in
the text above
Example 17
[0089] A spray gun was used to spray coat four different catalyst
slurries onto the cordierite sheet. The following four slurries and
the corresponding masks (referring to FIG. 2) were used: Zeolite Y
(mask A), Cu-ZSM-5 (mask B), Pt--Al.sub.2O.sub.3 (mask C), and
CeO.sub.2 (mask D).
[0090] After the spray coatings were completed, there were sixteen
individual and unique areas of the cordierite sheet with different
coatings. The coated sheet was calcinated to 1000.degree. F. for 2
hours to remove any moisture and organic components.
[0091] Circular sections were drilled out of the sheet in the
various unique areas. The drill bit used was a diamond-tipped
coring bit with an I.D. of 3.89 mm. The coatings held up very well
under the drilling process, and minimal flaking and damage was
observed under an optical microscope. The diameter of the circular
sections ranged between 3.5 and 3.6 mm.
[0092] The goal was to deposit approximately 0.0075 g/in.sup.2 of
each of the four slurries. The resulting coatings for the four
slurries were as follows: 0.0109 g/in.sup.2 of Zeolite Y, 0.0087
g/in.sup.2 of Cu-ZSM-5, 0.0094 g/in.sup.2 of Pt--Al.sub.2O.sub.3
and 0.0114 g/in.sup.2 CeO.sub.2. The coating quality was judged to
be excellent, with minimal intrusion into other areas and an
absence of patchy areas. When observed under an optical microscope,
the thickness of the individual coatings were measured at between
15-25 .mu.m, while the overall thickness of all four coatings was
observed to be between 70-90 .mu.m.
Example 18
[0093] Cordierite sheets were fired as previously described. A
screen printer was utilized to deposit catalyst ink onto a
6.75.times.6.75" sheet. This sheet was pre-perforated with 4 mm
diameter circular sections, and placed on top of a non-perforated
cordierite sheet (see FIG. 6). An alumina-containing ink was used
and deposited through a screen. The screen allowed for the
deposition of 32 identical 5/8" squares arranged in a 4 row.times.8
column pattern with 1/8" spacing on all sides.
[0094] The resulting coated sheet was calcinated at 540.degree. C.
for 2 hours.
[0095] The goal was to deposit approximately 0.01 g/in.sup.2 of the
ink, and the resulting calcined coating was 0.0097 g/in.sup.2.
Coating quality was excellent, with extremely sharp defined borders
and no intrusion into other areas. The observed thickness was
measured to be between 12 and 25 .mu.m.
[0096] Some of the pre-cut circular sections were removed for
further evaluation.
Example 19
[0097] Cordierite sheets were fired as previously described. A
screen printer was utilized to deposit catalyst ink onto
6.75.times.6.75" sheets. The sheets were pre-perforated with 4 mm
diameter circular sections. Each sheet was placed on top of a
non-perforated cordierite sheet (see FIG. 6). The screen pattern
was a simple 7.times.7" square, thus providing total coverage of
the surface of the cordierite sheet with a uniform coating. An
alumina-containing ink was applied.
[0098] The resulting coated sheets were calcined at 540.degree. C.
for 2 hours. The resulting depositions were 17.33 mg/in.sup.2 and
17.01 mg/in.sup.2, respectively, for two coated sheets. Some of the
pre-cut circular sections were selectively removed for further
evaluation.
Example 20
[0099] A screen printer was used to deliver varying amounts (weight
and/or thickness) of a particular component to different regions of
a 6.75.times.6.75" cordierite sheet fired as previously described.
This sheet was pre-perforated with 4 mm diameter circular sections,
and placed on top of a non-perforated-cordierite sheet (see FIG.
6). Three coatings of an ink containing 3% Pt/alumina were
delivered by using screens containing 32 discrete 5/8" squares
(arranged in different locations for each treatment). This resulted
in a series of square patterns containing 1, 2, or 3 coatings of
Pt/alumina. The resulting coated sheet was calcined at 540.degree.
C. for 2 hours. The first coating application led to deposition of
46.73 mg Pt/alumina per 5/8" square, while 41.72 mg and 46.84 mg
per square were delivered in second and third coatings,
respectively.
[0100] Four pellets, or circular sections with a 4 mm diameter,
were removed from the sheet, each pellet consisting of the
cordierite base and the catalyst coating on the top. All of the
samples were removed from regions that contained three coatings of
Pt/alumina as described above. The catalyst pellets were placed in
a reactor where gas containing 496 ppm of butane, 18% oxygen and
the remainder helium, was passed over each of the catalyst samples
individually. The gas exiting the reactor for each pellet was
analyzed by a scanning mass spectrometer. At 350.degree. C., the
conversion of butane to carbon dioxide was measured at 44.8%,
45.7%, 44.6% and 43.6%, respectively, for the four catalyst
samples. From these results, the average conversion for the
three-layer coating was determined to be 44.7%.
Example 21
[0101] Cordierite sheets were fired as previously described. A
screen printer was utilized to deposit a catalyst ink onto a
6.75.times.6.75" sheet.
[0102] The screen was a 6.times.6" gradient pattern with openings
ranging from 10% open area to 100% open area in 1% increments (90
steps total). The pattern on the screen can be described in terms
of dividing the entire area into a large number of cells. The
extent of exposure or opening of each cell is then gradually
increased across one axis. An example of such a pattern is shown in
FIG. 8 where the dark areas correspond to the openings or the
pattern that is generated upon coating. An ink containing 3%
Pt/alumina was used, and the resulting coating was excellent with
extremely sharp defined edging and no intrusion into other areas.
The resulting coating was calcined at 540.degree. C. for 2
hours.
Example 22
[0103] Cordierite sheets were fired as previously described. The
procedure described in Example 21 was followed, except after
deposition of the first coat, a second coat, containing a different
ink, with the configuration of the screen rotated 90.degree. with
respect to the first coating. The first ink contained 3%
Pt/alumina, while the second contained ceria. The final coated
sheet was dried at 90.degree. C. for one hour. The amount of dried
3% Pt/alumina ink deposited was 0.1732 grams, and the amount of
dried CeO2 ink deposited was 0.3403 grams. The resulting pattern
corresponds to the configuration shown in FIG. 7A.
[0104] Once given the above disclosure, many other features,
modifications, and improvements will become apparent to the skilled
artisan. Such other features, modifications, and improvements are,
therefore, considered to be a part of this invention, the scope of
which is to be determined by the following claims.
* * * * *