U.S. patent application number 12/211004 was filed with the patent office on 2009-03-19 for porous electrolessly deposited coatings.
This patent application is currently assigned to Velocys Inc.. Invention is credited to Haibiao Chen, Francis Daly, Richard Q. Long, Terry J. Mazanec.
Application Number | 20090075156 12/211004 |
Document ID | / |
Family ID | 40394532 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090075156 |
Kind Code |
A1 |
Long; Richard Q. ; et
al. |
March 19, 2009 |
Porous Electrolessly Deposited Coatings
Abstract
A new electroless plating approach to generate a porous metallic
coating is described in which a metal is electrolessly deposited on
a surface. Microparticles in the metal are removed to leave pores
in the metal coating. Another method of forming electroless
coatings is described in which a blocking ligand is attached to the
surface, followed by a second coating step. The invention includes
coatings and coated apparatus formed by methods of the invention.
The invention also includes catalyst structures comprising a dense
substrate and a porous metal adhered to the dense substrate, which
is further characterized by one or more of the specified
features.
Inventors: |
Long; Richard Q.; (New
Albany, OH) ; Daly; Francis; (Delaware, OH) ;
Chen; Haibiao; (Dublin, OH) ; Mazanec; Terry J.;
(Powell, OH) |
Correspondence
Address: |
FRANK ROSENBERG
P.O. BOX 29230
SAN FRANCISCO
CA
94129-0230
US
|
Assignee: |
Velocys Inc.
Plain City
OH
|
Family ID: |
40394532 |
Appl. No.: |
12/211004 |
Filed: |
September 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60972210 |
Sep 13, 2007 |
|
|
|
Current U.S.
Class: |
429/416 ;
427/343; 427/404; 428/172; 502/200 |
Current CPC
Class: |
C23C 18/1662 20130101;
H01M 4/9041 20130101; Y02E 60/50 20130101; H01M 4/8621 20130101;
C23C 18/44 20130101; C23C 18/1692 20130101; Y10T 428/24612
20150115; H01M 4/9016 20130101; H01M 4/92 20130101; H01M 4/8825
20130101; H01M 4/8652 20130101 |
Class at
Publication: |
429/40 ; 427/343;
428/172; 427/404; 502/200 |
International
Class: |
H01M 4/86 20060101
H01M004/86; B05D 3/10 20060101 B05D003/10; B05D 1/36 20060101
B05D001/36; B01J 27/24 20060101 B01J027/24; B32B 3/30 20060101
B32B003/30 |
Claims
1. A computer-implementable method comprising: transmitting, from a
transmitting computer to a receiving computing device, three
options for accepting a message from the transmitting computer,
wherein the message includes a text component and an audio content;
presenting on a video display at the receiving computing device, a
first option, a second option, and a third option for accepting the
message, wherein the first option is to accept the message at the
receiving computing device with the audio content attached and
fully enabled for activation upon receipt of the message, wherein
the second option is to accept both the text component and the
audio content of the message but to contemporaneously and
temporarily disable the audio content by disabling a sound card on
the receiving computing device upon receipt of the message, and
wherein the third option is to accept only the text component of
the message while rejecting a receipt of the audio content;
receiving, by the transmitting computer, a signal indicating which
of the three options has been selected by a user of the receiving
computing device for receiving the message; in response to the user
selecting the first option: transmitting the message from the
transmitting computer to the receiving computing device with the
audio content attached to the message, and activating the audio
content immediately upon the receiving computing device receiving
the message; in response to the user selecting the second option:
transmitting the message from the transmitting computer to the
receiving computing device with the audio content attached to the
message, and remotely and temporarily disabling, by the remote
transmitting computer, the audio content at the receiving computing
device by temporarily disabling the sound card on the receiving
computing device; and in response to the user selecting the third
option: transmitting the message from the transmitting computer to
the receiving computing device without the audio content attached
to the message.
2-8. (canceled)
9. A system comprising: a processor; a data bus coupled to the
processor; a memory coupled to the data bus; and a computer-usable
medium embodying computer program code, the computer program code
comprising instructions stored in a tangible medium and executable
by the processor and configured to: transmit, from a remote
transmitting computer to a receiving computing device, three
options for receiving an Instant Messaging (IM) message from the
remote transmitting computer, wherein the IM message includes a
text component and an audio streaming content, wherein a first
option is to receive the IM message at the receiving computing
device with the audio streaming content attached and fully enabled,
wherein a second option is to receive the IM message with the audio
streaming content attached but to contemporaneously and temporarily
disable the audio streaming content upon receipt of the IM message,
and wherein a third option is to receive the IM message without the
audio streaming content being attached; receive, by the remote
transmitting computer, a signal indicating which of the three
options has been selected by a user of the receiving computing
device for receiving the IM message; in response to the user
selecting the first option: transmit the IM message to the
receiving computing device with the audio streaming content
attached to the IM message, and activate the audio streaming
content immediately upon the receiving computing device receiving
the IM message; in response to the user selecting the second
option: transmit the IM message to the receiving computing device
with the audio streaming content attached to the IM message;
remotely and temporarily disable, by the remote transmitting
computer, the audio streaming content at the receiving computing
device by temporarily disabling a sound card on the receiving
computing device, and subsequently reactivate the audio streaming
content in response to the user plugging headphones into the
receiving computing device to disable loudspeakers on the receiving
computing device; and in response to the user selecting the third
option: transmit the IM message without the audio streaming content
attached to the IM message, and subsequently reoffer the first and
second option to the user of the receiving computing device.
10-12. (canceled)
13. A tangible computer-usable storage medium on which is stored
computer program code, the computer program code comprising
computer executable instructions configured to: transmit, from a
remote transmitting computer to a receiving computing device, three
options for receiving an Instant Messaging (IM) message from the
remote transmitting computer, wherein the IM message includes a
text component and an audio streaming content, wherein a first
option is to receive the TM message at the receiving computing
device with the audio streaming content attached and fully enabled,
wherein a second option is to receive the IM message with the audio
streaming content attached but to contemporaneously and temporarily
disable the audio streaming content upon receipt of the IM message,
and wherein a third option is to receive the IM message without the
audio streaming content being attached; receive, by the remote
transmitting computer, a signal indicating which of the three
options has been selected by a user of the receiving computing
device for receiving the IM message; in response to the user
selecting the first option: transmit the IM message to the
receiving computing device with the audio streaming content
attached to the IM message, and activate the audio streaming
content immediately upon the receiving computing device receiving
the IM message; in response to the user selecting the second
option: transmit the IM message to the receiving computing device
with the audio streaming content attached to the IM message;
remotely and temporarily disable, by the remote transmitting
computer, the audio streaming content at the receiving computing
device by temporarily disabling a sound card on the receiving
computing device, and subsequently reactivate the audio streaming
content in response to the user plugging headphones into the
receiving computing device to disable loudspeakers on the receiving
computing device; and in response to the user selecting the third
option: transmit the IM message without the audio streaming content
attached to the IM message, and subsequently reoffer the first and
second option to the user of the receiving computing device.
14-25. (canceled)
26. The computer-implemented method of claim 1, wherein the audio
content is embedded directly into the message.
27. The computer-implemented method of claim 1, wherein the audio
content is an audio file that is stored in the remote transmitting
computer.
28. The computer-implemented method of claim 1, wherein the audio
content is a streaming content.
29. The computer-implemented method of claim 28, wherein the
streaming content is generated by a streaming media source
point.
30. The computer-implemented method of claim 1, wherein the user
has selected the second option, and wherein the sound card is
re-activated only after a volume level on the receiving computing
device is adjusted downward.
31. The computer-implemented method of claim 1, wherein the user
has selected the second option, and wherein the sound card is
re-activated only after the user plugs a set of headphones into the
receiving computing device.
32. The computer-implemented method of claim 1, wherein the user
has selected the third option, and wherein the computer-implemented
method further comprises subsequently reoffering the first option
and the second option to the user of the receiving computing device
in response to the user selecting the third option.
33. The computer-implemented method of claim 1, wherein the user
has selected the third option, and wherein the receiving computing
device is permanently prevented from aurally presenting the audio
content unless the user subsequently selects the first option or
the second option.
Description
RELATED APPLICATIONS
[0001] In accordance with 35 U.S.C. sect. 119(e), this application
claims priority to U.S. Provisional Application No. 60/972,210,
filed Sep. 13, 2007.
INTRODUCTION
[0002] There has been a long history of work devoted to forming
porous metal coatings. For example, in U.S. Pat. No. 1,628,190,
issued in 1927, Raney described a method of making porous nickel by
alloying the nickel with aluminum and subsequently dissolving the
aluminum to leave porous nickel.
[0003] More recently, there has been a great deal of interest in
forming metallic coatings in microchannels. Tonkovich et al. in WO
2006/127889A2 (PCT/US2006/020220, which is incorporated herein as
if reproduced in full) describe a variety of microchannel apparatus
and numerous ways of forming catalysts on microchannel walls
including designs for structured walls that may be subsequently
coated with a catalyst. The patent also mentions the use of a
polymeric templating agent followed by treatment with a metallic
templating agent and an oxidation step to form a porous metallic
structure.
[0004] Electroless plating of metals such as platinum on substrates
has attracted much interest because it can improve resistance to
corrosion and abrasion, or increase desirable electrical
properties, or act as catalysts for various chemical reactions. Pt
and Pt-alloy catalysts have been widely used as catalysts for
various chemical reactions, such as steam methane reforming,
partial oxidation, CO.sub.2 reforming, auto-thermal reforming of
gasoline, combustion, ammonia oxidation, dehydrogenation and
hydrocracking of alkanes, oxidative dehydrogenation of alkanes and
NOx abatement in automotive emission control. They are also used as
anode and cathode catalysts in low-temperature fuel cells such as
alkaline fuel cell, phosphoric acid fuel cell, proton exchange
membrane fuel cell and direct methanol fuel cell. It is expected
that higher Pt surface area will result in higher catalytic
activity. However, electroless plating and electroplating usually
generate a dense Pt layer with low surface area.
[0005] In U.S. Pat. No. 3,486,928 (1969), Rhoda and Vines used a
solution containing Na.sub.2Pt(OH).sub.6, NaOH, ethylamine and
hydrazine for electroless Pt plating. However, hydrazine is not
stable in this system and thus needs to be added in situ. In DE
patent 2607988 (1977), JP patent 84-80764 (1984) and U.S. Pat. No.
6,391,477 (2002), Pt(NH.sub.3).sub.2(NO.sub.2).sub.2 was used as a
Pt salt and hydrazine was a reducing agent for plating.
Pt(NH.sub.3).sub.2(NO.sub.2).sub.2 salt is hard to dissolve into
water. In order to increase its solubility, sometimes ammonium
hydroxide is added in the solution. This will bring some challenges
in plating Pt in small channels, such as microchannel devices. Many
plating steps are necessary to reach targeted loadings. For
instance, to get 10 mg/in.sup.2 Pt loading in a microchannel with a
dimension of 1 inch.times.0.18 inch.times.0.046 inch, it needs 17
plating processes by using a solution with 2 g/L Pt solution (e.g.,
Pt(NH.sub.3).sub.2(NO.sub.2).sub.2 salt). By comparison, it needs
only one coat if a 30 g/L Pt solution is used. We discovered that
Pt(NH.sub.3).sub.4(NO.sub.3).sub.2 and Pt(NH.sub.3).sub.4(OH).sub.2
can be used as Pt salts for electroless plating. Both salts can
dissolve into water in a large amount. However, as described above,
the generated Pt layer has low Pt surface area.
[0006] German patent DE2607988 (1977) reported an example of an
electroless rhodium plating bath using rhodium ammine nitrite,
i.e., (NH.sub.3).sub.xRh(NO.sub.2).sub.y, hydrazine as reducing
agent, and ammonium hydroxide as complexing agent. The rhodium
ammine nitrite was prepared by reaction of rhodium chloride with
excess sodium nitrite and ammonium hydroxide. Similarly, U.S. Pat.
No. 6,455,175 (2002) reported a composition for electroless Rh
plating using rhodium ammine nitrite, ammonium hydroxide and
hydrazine hydrate. The rhodium ammine nitrite was synthesized by
reacting K.sub.3[Rh(NO.sub.2).sub.3Cl.sub.3] with NH.sub.4OH in
this patent. For these two processes, the Rh reduction process is
so fast that many bubbles are generated. Rh precipitation is also
seen in the solution. It is clear that these plating processes are
impractical for coating a microchannel device due to bubble
formation and Rh precipitation. Also the bubbles promote
non-uniformity of the Rh coating. The Rh precipitation also results
in a high cost because Rh is expensive. JP58204168 (1983) provided
a Rh plating bath using rhodium ammine chloride, a hydroxyl amine
salt as a stabilizer and hydrazine as a reducing agent. The
Rh(NH.sub.3).sub.6Cl.sub.3 was prepared by reacting RhCl.sub.3 with
concentrated NH.sub.4OH at 150.degree. C. and 20 atm in an
autoclave. However, the Rh(NH.sub.3).sub.6Cl.sub.3 is only slightly
soluble in water and thus makes the plating process costly for
handling so much waste liquid. Also many plating cycles are
necessary to get the targeted loading for microchannel device due
to the low volume/surface ratio.
[0007] JP2000282248 (2000) reported Rh plating baths with
ammonium-di(pyridine-2,6-dicarboxylate)-rhodium (III),
RhCl.sub.x(NH.sub.3).sub.6-x (x denotes 0 to 3), rhodium acetate, a
triethylenetetramine complex of rhodium chloride or a
diethylenetriamine complex of rhodium. The deposition is executed
preferably at a pH 8 to 9 at 70-95.degree. C. While electroless
plating has many advantages over other plating methods, including
the ability to plate almost any substrate and the ability to
achieve uniform coating loadings over objects of almost any shape,
coatings prepared by electroless plating are dense with low surface
area. Conventional electroless plated coatings require high metal
loadings and produce low surface area coatings which limits their
utility, particularly for catalytic applications of precious metals
wherein effective use of the expensive metals is important for
economic as well as technical reasons. Thus a need exists for an
electroless plating process that produces a porous, high surface
area coating and can be used with precious metals as well as other
metals.
SUMMARY OF THE INVENTION
[0008] This invention provides a new electroless plating approach
to generate a porous metallic coating. The porous catalyst metal
has a higher surface area and thus will exhibit higher activities
in chemical reactions. The porous coating requires lower metal
loading to achieve the same exposed surface area thus producing a
more economically attractive coating. The electroless plating
approach deposits a metal such as Pt, Pd, Rh, Ag, Cu, Au, Fe, Co,
Re, and their alloys. For example, the formed porous Pt can be used
for preparing Pt alloy catalysts, e.g., Pt--Rh, Pt--Pd, Pt--Au,
Pt--Pd--Au, Pt--Cu and Pt--Ag.
[0009] In a first aspect, the invention provides a method of
forming a metal coating on a substrate, comprising: providing a
liquid composition comprising a metal complex; contacting the
substrate with microparticles; contacting the substrate with the
liquid composition; reacting the metal complex with a reducing
agent; and removing the microparticles to form a porous metal
coating on the substrate. The porous metal coating contains pores
dispersed in the metal coating that correspond in size to the
microparticles. At least initially the size of the microparticles
and the pores is about the same since the particles are oxidized or
dissolved away; however, the pore sizes may change if the porous
meal coating is subsequently heated or subjected to corrosive
conditions. The invention also includes metal coatings or membranes
made by this method. The invention also includes microchannel
apparatus in which at least one interior microchannel wall
comprises a porous metal coating made by the inventive method.
[0010] In some embodiments, the porous coating is modified by
addition of additional metals, oxides or sols. In some preferred
embodiments, the reducing agent is added to the composition prior
to adding the composition into a microchannel. Alternatively, the
reducing agent can be added after contacting the liquid composition
and the substrate. Preferably, the microparticles are polymeric
microspheres that are removed by calcining in the presence of
oxygen.
[0011] In another aspect, the invention provides a catalyst
structure, comprising: a dense substrate, and a porous metal
adhered to the dense substrate, and one or more of the following
features: a second material (in addition to the porous metal)
filling the pores in the porous metal, wherein the second material
comprises an ionic conductor; or an average pore size of at least 1
micron in the porous metal; or a bi-modal distribution of pore
sizes in the porous metal; or the surface area of the porous metal
exceeds 100 m 2/m3. The inventive structure can comprises any
combination of the features mentioned above. Preferably, the dense
substrate comprises a metal wall of a microchannel apparatus. In
another embodiment, the dense substrate comprises an electrode. The
invention also includes microchannel apparatus such as a chemical
reactor, chemical separator, or fuel cell comprising the inventive
structure.
[0012] In a further aspect, the invention provides a method of
forming layers of a metal on a surface, comprising: (1)
electrolessly plating metal onto a surface; (2) attaching a
blocking ligand to the electrolessly plated metal; and (3)
electrolessly plating the same or a different metal onto the
material resulting from step (2).
[0013] In another aspect, the invention provides a method of making
the membrane and the resulting membrane. A membrane can be formed
by removing the coating from a substrate to form a film-like (or
ribbon) material that can be treated from opposite sides to
partially or completely fill the pores. In another embodiment the
membrane can be formed by electrolessly plating on a porous
substrate containing pores sufficiently small holes or pores that
they are filled by the plating metals. The active membrane material
could be the porous substrate, the electroless plated metal(s) or
the combination of the two phases. In still another embodiment, a
previously prepared membrane that contains small holes can be made
leak-free by conducting the electroless plating by introducing the
metal and reducing agents from opposing sides of the membrane and
allowing them to react at the holes between the two sides, plating
within these pores and thus sealing the membrane.
Glossary
[0014] A "bimodal pore distribution" is in a material in which
there pores are substantially divided into two distinct and
non-overlapping size ranges: a first group composed of relatively
large pores that correspond to the size of the microparticles, and
a second group of relatively small pores. Preferably, the large
pores are in the size range of 0.1 to 10 micrometers (.mu.m) and
the small pores are 10 nm or less and in some embodiments in the
range from 1 to 10 nm. Preferably, at least 90%, more preferably at
least 95%, of total pore volume is within the two ranges that
define the bimodal distribution.
[0015] A "complex microchannel" is in apparatus that includes one
or more of the following characteristics: at least one contiguous
microchannel has a turn of at least 45.degree., in some embodiments
at least 90.degree., in some embodiments a u-bend; a length of 50
cm or more, or a length of 20 cm or more along with a dimension of
2 mm or less, and in some embodiments a length of 50-500 cm; at
least one microchannel that splits into at least 2
sub-microchannels in parallel, in some embodiments 2 to 4
sub-channels in parallel; at least 2 adjacent channels, having an
adjacent length of at least one cm that are connected by plural
orifices along a common microchannel wall where the area of
orifices amounts to 20% or less of the area of the microchannel
wall in which the orifices are located and where each orifice is
1.0 mm.sup.2 or smaller, in some embodiments 0.6 mm2 or smaller, in
some embodiments 0.1 mm2 or smaller--this is a particularly
challenging configuration because a coating should be applied
without clogging the holes; or at least two, in some embodiments at
least 5, parallel microchannels having a length of at least 1 cm,
have openings to an integral manifold, where the manifold includes
at least one dimension that is no more than three times the minimum
dimension of the parallel microchannels (for example, if one of the
parallel microchannels had a height of 1 mm (as the smallest
dimension in the set of parallel microchannels), then the manifold
would possess a height of no more than 3 mm). An integral manifold
is part of the assembled device and is not a connecting tube. A
complex microchannel is one type of interior microchannel.
[0016] The electrolessly deposited coatings are preferably
post-assembly coatings. A "post-assembly" coating is applied onto
three dimensional microchannel apparatus. This is either after a
laminating step in a multilayer device made by laminating sheets or
after manufacture of a manufactured multi-level apparatus such as
an apparatus in which microchannels are drilled into a block. This
"post-assembly" coating can be contrasted with apparatus made by
processes in which sheets are coated and then assembled and bonded
or apparatus made by coating a sheet and then expanding the sheet
to make a three-dimensional structure. For example, a coated sheet
that is then expanded may have uncoated slit edges. Uncoated
surfaces of all types, such as slit edges, can undergo corrosion or
reaction under reaction conditions. Thus, it is advantageous to
coat the device after assembly to protect all of the internal
surface against corrosion. The post-assembly coating provides
advantages such as crack-filling and ease of manufacture.
Additionally, the aluminide or other coating could interfere with
diffusion bonding of a stack of coated sheets and result in an
inferior bond since aluminide is not an ideal material for bonding
a laminated device and may not satisfy mechanical requirements at
high temperature. Whether an apparatus is made by a post-assembly
coating is detectable by observable characteristics such as
gap-filling, crack-filling, elemental analysis (for example,
elemental composition of sheet surfaces versus bonded areas)
Typically, these characterisitics are observed by optical
microscopy, electron microscopy or electron microscopy in
conjunction with elemental analysis. Thus, for a given apparatus,
there is a difference between pre-assembled and post-assembled
coated devices, and an analysis using well-known analytical
techniques can establish whether a coating was applied before or
after assembly (or manufacture in the case of drilled
microchannels) of the microchannel device.
[0017] A "separator" is a type of chemical processing apparatus
that is capable of separating a component or components from a
fluid. For example, a device containing an adsorbent, distillation
or reactive distillation apparatus, etc.
[0018] Microchannel reactors are characterized by the presence of
at least one reaction channel having at least one dimension
(wall-to-wall, not counting catalyst) of 1.0 cm or less, preferably
2.0 mm or less (in some embodiments about 1.0 mm or less) and
greater than 100 nm (preferably greater than 1 em), and in some
embodiments 50 to 500 .mu.m. A reaction channel is a channel
containing a catalyst. Microchannel apparatus is similarly
characterized, except that a catalyst-containing reaction channel
is not required. Both height and width are substantially
perpendicular to the direction of flow of reactants through the
reactor. Microchannels are also defined by the presence of at least
one inlet that is distinct from at least one outlet--microchannels
are not merely channels through zeolites or mesoporous materials.
The height and/or width of a reaction microchannel is preferably
about 2 mm or less, and more preferably 1 mm or less. The length of
a reaction channel is typically longer. Preferably, the length of a
reaction channel is greater than 1 cm, in some embodiments greater
than 50 cm, in some embodiments greater than 20 cm, and in some
embodiments in the range of 1 to 100 cm. The sides of a
microchannel are defined by reaction channel walls. These walls are
preferably made of a hard material such as a ceramic, an iron based
alloy such as steel, or a Ni--, Co-- or Fe-based superalloy such as
monel. The choice of material for the walls of the reaction channel
may depend on the reaction for which the reactor is intended. In
some embodiments, the reaction chamber walls are comprised of a
stainless steel or Inconel.RTM. which is durable and has good
thermal conductivity. The alloys should be low in sulfer, and in
some embodiments are subjected to a desulferization treatment prior
to formation of an aluminide. Typically, reaction channel walls are
formed of the material that provides the primary structural support
for the microchannel apparatus. The microchannel apparatus can be
made by known methods (except for the coatings and treatments
described herein), and in some preferred embodiments are made by
laminating interleaved plates (also known as "shims"), and
preferably where shims designed for reaction channels are
interleaved with shims designed for heat exchange. Some
microchannel apparatus includes at least 10 layers laminated in a
device, where each of these layers contain at least 10 channels;
the device may contain other layers with fewer channels.
BRIEF DESCRIPTION OF THE FIGURES
[0019] FIG. 1 is a SEM micrograph of Pt plated coupon without
microspheres (example 1).
[0020] FIG. 2 is a SEM micrograph of Pt plated coupon with
microsphere washcoating (example 2).
[0021] FIG. 3 is a SEM micrograph of Pt plated coupon with
microspheres in plating solution (example 3).
[0022] FIG. 4 shows SEM micrographs of a porous Pt layer that has
been subsequently plated with Rh.
[0023] FIG. 5 is a SEM micrograph of a Pt plated coupon with PVA in
the plating solution (example 6).
[0024] FIG. 6 shows a SEM micrograph of a Pt plated coupon that was
formed without microparticles and calcined at 900.degree. C. in
air.
[0025] FIG. 7 shows SEM micrographs of a porous Pt layer (such as
Example 3) after calcining in air at various times.
DESCRIPTION OF THE INVENTION
[0026] The solid metal coating is formed from a liquid composition
(a metal complex is dissolved in a liquid). The starting material
typically comprises an aqueous solution of a metal complex. The
metal complex could be any metal complex suitable for use in
electroless plating. Examples include Pt(NH.sub.3).sub.4(OH).sub.2
and Rh amine hydroxide Rh(NH.sub.3).sub.2X(OH).sub.y. The technique
is broadly applicable to metals that can be deposited by
electroless plating. A nonlimiting list of other potential ligands
includes nitrates, nitrites, chlorides, bromides, iodides,
sulfates, sulfites, phosphates, phosphites, acetates, and oxalates.
In preferred embodiments, the liquid composition comprises Pt, Pd,
Rh, Ag, Cu, Au, Fe, Co, or Re, or combinations of these metals.
These metals have known methods for electroless deposition and can
be useful catalysts. In some preferred embodiments, the liquid
composition comprises 0.0001 weight % to 2.0 weight % of a metal or
metals, more preferably 0.2 to 2.0 weight percent (more preferably
one or more metals selected from Pt, Pd, Rh, Ag, Cu, Au, Fe, Co,
and Re). Weight percent refers to the mass of metal atoms divided
by the mass of liquid composition multiplied by 100. The liquid
composition preferably has a pH of at least 5.
[0027] Polymers or other removable small particles can be added to
the electroless plating solution during the plating or washcoated
on the substrate prior to plating. The polymers can be, but are not
limited to, polystyrene latex, polyethylene, polyethylene glycols
and their derivatives, aldehyde polymers, polyethylene oxides,
poly(2-ethyl-2-oxazoline), polypropylene glycols, polystyrene,
polyvinyl acetate, polyvinyl alcohol, polyvinylpyrrolidone,
polyoxyalkylenes, polyesters and polycarbonates. The polymer is
preferably in the form of polymer microparticles. The
microparticles are preferably approximately spherical, but could be
other shapes such as rods or irregular shapes. Materials that
volatilize when heated in the presence of oxygen are particularly
desirable since they can easily be removed by calcination; however,
dissolvable materials could also be used and removed by treatments
with the appropriate solvent(s). In one preferred embodiment, a
surface is pretreated with an aqueous dispersion of polymer
particles. In another preferred embodiment, the electroless plating
composition (which is preferably aqueous) comprises a metal complex
and a dispersion of polymer particles and the metal and polymer are
deposited in the same step.
[0028] The microparticles could comprise any material that can
readily be incorporated in the coating during electroless plating
and at least partially removed after the electroless plating step.
Hydrocarbons such as polymers, carbon, waxes, starch, or the like
can be incorporated and removed later, for example by pyrolysis or
combustion or solvent extraction. The microparticles could also
comprise mixtures of removable and non-removable materials. The
non-removable materials are those which are not removed by
combustion or solvent extraction. When solvent extraction is used,
the solvent is typically an organic solvent. The non-removable
material(s) could be separate particles or within the same
particles as the removable material. The non-removable materials
may include sol or gel precursors, metal oxides, metal particles,
or the like. Materials that are not removed from the coated layer
could provide additional catalytic functionality (for example a
bimetallic catalyst), or inhibit sintering of the porous metallic
structure, or provide other functionality. When the non-removable
material is within the same particle as the removable material, the
resulting structure may have the non-removable material exposed
within the pores. In some cases, the non-removable material could
be selected to migrate into and/or react with the deposited metal
during the burn out or a subsequent heat treatment. Some preferred
non-removable materials include zeolites, AL.sub.2O.sub.3,
SiO.sub.2, ZrO.sub.2, TiO.sub.2, CeO.sub.2, MgO and their
mixtures.
[0029] The size of the microparticles is preferably in the range of
0.001 to 1000 microns (.mu.m), more preferably 0.01 to 100 microns,
in some embodiments at least 1 .mu.m, and in some embodiments in
the range of 0.1 to 10 microns. After particle removal, the metal
is left with pores having the sizes of the removed particles. In
some cases, two or more types of particles could be used; a first
type that is removed first (such as by a solvent) and a second type
that is removed subsequently (such as by calcining or by a second
solvent). This could be used to create a bimodal pore distribution.
To form an interpenetrating network, a second material could be
used to fill the pores. The metal and the microparticles could be
applied on any substrate, including powders (oxides, catalyst
supports, zeolites, etc.), glass, fibers, ceramic materials and
metallic materials. The substrates could have a flat surface or a
modified surface with various geometries (e.g., pores or
microchannels). The surface of the substrates may be treated with
other metals, such as Cu, Pt and Pd, prior to plating with Rh or
another metal. This process can also be used for plating alloys
(e.g., Pt--Rh alloy) simultaneously. The substrate surface may also
be modified with pre-coating with metal, transition metal oxide,
rare earth oxide, alkaline earth oxide or combinations of these
prior to electroless plating. Treatment with a pre-coat of a metal
oxide (preferably comprising a rare earth metal oxide) can enhance
adhesion of the electrolessly applied metal. The substrates can be
a flat surface (for example, a flat channel wall), a surface
modified with various geometries (e.g., etched features,
microchannel walls with patterned features), foam, felt, etc.
[0030] In their broader aspects, the inventive techniques are
applicable to a wide variety of substrates includes metals,
ceramics and plastics of any shape. Dense substrates are preferably
metals (not porous metals) as are well-known conventional materials
such as steel, stainless steel, and superalloys. In particularly
preferred embodiments, the porous metal coating is formed on one or
more surfaces of a microchannel (or, more typically, microchannels)
within a microchannel device. Microchannels have at least one
dimension of 1 cm or less, preferably 2 mm or less, and in some
embodiments 0.1 mm to 1 mm. Microchannel apparatus is well known
and we have found that electroless plating is especially
well-suited to coat the microchannels. The invention is especially
useful in forming post-assembly coatings and forming coatings on
microchannel walls in complex microchannels.
[0031] Microchannel apparatus typically contains numerous channels.
In many applications, the electroless plating solution is added to
selected channels; for example, at least 3 channels are treated
with an electroless plating solution while at least 2 other
channels in the same apparatus are not treated. In some preferred
embodiments, all sides of a selected microchannel (as opposed to a
single side) are coated with a catalytic metal. The catalyst
material can comprise a porous metal or an interpenetrating
network.
[0032] Substrates for interpenetrating networks can be any of the
substrates previously mentioned. In a preferred embodiment, the
substrate is a dense material, preferably a metal. The
electrolessly applied coating adheres to the substrate and may have
any of the pore sizes (or, in the case of an IPN, a second material
filling the pores) mentioned previously.
[0033] The invention is broadly applicable for a variety of
electroless plating conditions. The metal layer is deposited from
solution by reacting a metal complex with a reducing agent.
Typically, reducing agents could include hydrazine, sodium boron
hydride, sodium hypophosphite, dimethyl amine borane, diethyl amine
borane and sodium borohydride, and mixtures thereof, preferably
hydrazine or sodium borohydride. At the time of deposition, the pH
of the solution (liquid composition plus reducing agent, plus any
additional optional components) is preferably at least 10. The
deposition can be conducted at room temperature, or at elevated
temperatures for faster deposition.
[0034] After the electroless formation of a layer, the removable
material such as a polymer(s) is removed and a porous metal layer
is formed. The polymer(s) is removed by calcination or by
dissolving in solvents. The calcination temperature could be in the
range of 100-800.degree. C., preferably 400-600.degree. C. The
solvents could include alcohol, hydrocarbons, acetone, benzenes,
and any other organic solvents.
[0035] Polymers are preferably removed from the plating by
calcination in the presence of oxygen at a temperature of at least
400.degree. C. In some embodiments, the calcination is conducted in
the presence of flowing air or oxygen.
[0036] The porous Rh and Pt have high surface area and could be a
superior electroless plated catalyst for various chemical
reactions, such as steam reforming, especially steam methane
reforming (SMR), partial oxidation, selective oxidation, and
combustion. Electroless plated rhodium metal exhibits good
catalytic performance for steam methane reforming and fuel-rich
combustion. As compared to slurry washcoating, electroless plating
of Rh is a simpler and higher quality technique, especially for
microchannel channel devices with jet hole designs for the staged
addition of a chemical reactant, e.g., oxygen. It is expected that
a porous Rh surface will exhibit higher catalytic activity than a
non porous or dense Rh plated surface due to its higher surface
area.
[0037] The resulting electrolessly deposited metals can have a
well-defined porosity (controlled by the size of the particles).
For example, if desired, the pore sizes can be highly uniform with
80% or more of the pore volume comprised of pores that vary in size
by 20% or less (as measured by BET or Hg porosimetry). In preferred
embodiments, the porous structure is random and isotropic.
[0038] In some cases, a second metal can be coated over the porous
metal layer. The second metal can be deposited either in the
presence or absence of microparticles. This could be repeated for
any desired number of layers.
[0039] The porous coated surface formed by electroless plating of
metals in the presence of microparticles could be further
functionalized by addition of metals, oxides, or other materials to
form an interpenetrating network of two or more materials after the
removal of the removable material. The addition could be by
impregnation, vapor coating, electroless coating, or other
technique. The added material could provide additional catalytic
activity, modify the activity of the deposited porous material,
provide structural support, or inhibit structural evolution under
processing or process conditions. The added material could also
have transport properties, such as oxide, hydroxyl or hydrogen ion
conductivity. Such an interpenetrating network is expected to be an
excellent electrode for a fuel cell, battery or other electrical
device. An interpenetrating network of materials with electrical
conductivity and ion conductivity could also function as a
membrane. Preferred materials with ionic conductivity include
oxides of zirconia, optionally stabilized in the cubic form with
Mg, Ca, Y or other rare earth metal, ceria, optionally stabilized
by Gd, Eu or other rare earth metal, perovskites of formulation
M1M20x wherein M1 is chosen from among Fe, Co, Cr, or some
combination, M2 is chosen from among Ba, Sr, La, rare earths, or
some combination thereof, BiVMOx materials, where M can be any
transition metal or combination thereof. Preferably the fractional
volume of the electrical conducting phase in the IPN of electrical
and ion conductive phases is between 0.1 and 0.9, more preferably
0.2 and 0.8 and most preferably between 0.3 and 0.7. Particularly
advantaged combinations are Pt as the metallic phase and
yttria-stabilized zirconia as the oxide conducting phase, and other
combinations as described in U.S. Pat. No. 5,306,411 which is
incorporated herein by reference.
[0040] Examples of making porous electrolessly deposited coatings
have been shown with Rh, Pt, and Pt--Rh. In one example, an alumina
surface was treated with an aqueous composition containing
Pt(NH.sub.3).sub.4(OH).sub.2, hydrazine, and 1.75 micrometer
polystyrene microspheres for several hours. The coating was dried
and calcined in air. The resulting Pt coating was highly porous.
Then, a Rh layer was electrolessly deposited in the absence of
microspheres. Surprisingly, the Rh layer deposited at a rate
several times greater as compared to Rh deposition on a
conventional Pt layer (prepared without microspheres). The coatings
have been characterized by SEM and tested for catalyzing fuel-rich
combustion in a microchannel. The catalyst prepared using
microspheres contained a much higher Rh concentration (due to the
faster deposition rate) and demonstrated substantially improved
combustion performance. Electroless plating of Rh in the presence
of microspheres similarly resulted in a porous Rh coating.
EXAMPLE 1 (REFERENCE)
[0041] A solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2
wt % Pt) and 0.2 wt % N.sub.2H.sub.4H.sub.2O was prepared. An
aluminized alloy 617 coupon was heat-treated at 1050.degree. C. for
10 hours before use. The surface of this coupon was covered by an
.alpha.--Al.sub.2O.sub.3 scale. The coupon was hung in the solution
at room temperature overnight. 11.4 mg/in2 Pt was plated on the
coupon. After that, the Pt plated coupon was put in a new Pt
plating solution with the same composition for 3 hours. Next the
coupon was cleaned and calcined at 500.degree. C. for 1 h in air.
The final Pt loading was 15.7 mg/in2. The SEM micrograph shows that
the Pt layer is flat and dense (FIG. 1).
EXAMPLE 2
[0042] An aluminized Inconel 617, heat treated and Pt-plated coupon
(15 mg/in2 Pt) was coated with 0.11 mg polystyrene microsphere (1.7
.mu.m) and dried at room temperature. Next the coupon was put in a
solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt)
and 0.2 wt % N.sub.2H.sub.4H.sub.2O for 20 hours at room
temperature. The coupon was then cleaned and calcined at
500.degree. C. for 1 h in air. 11 mg/in.sup.2 Pt was plated on the
coupon. SEM micrograph shows that the surface Pt layer is porous
(FIG. 2). Bimodal pores (1.7 .mu.m and 50-100 nm) are observed.
EXAMPLE 3
[0043] An aluminized Inconel 617, heat treated and Pt-plated coupon
(15 mg/in2 Pt) was put in a solution consisting of
Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt), 0.2 wt %
N.sub.2H.sub.4H.sub.2O and 1.0 wt % polystyrene microsphere (1.7
.mu.m) for 20 hours at room temperature. The coupon was then
cleaned and calcined at 500.degree. C. for 1 h in air. 12
mg/in.sup.2 Pt was plated on the coupon. SEM micrograph shows that
the surface Pt layer is very porous (FIG. 3). Pt particle size is
in the range of 100 to 200 nm.
EXAMPLE 4
[0044] An aluminized Inconel 617 coupon is heat-treated at
1050.degree. C. for 10 hours prior to use. The surface of the
coupon is covered with an .alpha.--Al.sub.2O.sub.3 scale. The
coupon is then put in a solution consisting of
Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt) and 0.2 wt %
N.sub.2H.sub.4H.sub.2O. The plating is performed at room
temperature for 4 hours. The Pt loading is 3.0 mg/in.sup.2. The
Pt-plated coupon was put in a solution consisting of 0.23 wt % Rh
as Rh(NH.sub.3).sub.X(OH).sub.3, 4.4 wt % NH.sub.4OH, 15.4 wt %
N.sub.2H.sub.4H.sub.2O and 1.0 wt % polystyrene microsphere (1.75
.mu.) for 21 hours at room temperature. The coupon was rinsed with
H.sub.2O and calcined at 500.degree. C. for 1 h in air. 10
mg/in.sup.2 Rh was plated on the coupon. SEM micrographs show that
the Rh layer consists of porous and tri-modal as illustrated in
FIG. 4.
EXAMPLE 5
[0045] A solution consisting of Pt(NH.sub.3).sub.4(OH).sub.2, (0.2
wt % Pt) and 0.2 wt % N.sub.2H.sub.4H.sub.2O was prepared. An
aluminized alloy 617 coupon was heat-treated at 1050.degree. C. for
10 hours before use. The surface of this coupon was covered by an
.alpha.---Al.sub.2O.sub.3 scale. The coupon was hung in the
solution at room temperature for 16 hours. 7 mg/in2 Pt was plated
on the coupon. After that, the Pt plated coupon was put in a new Pt
plating solution with the same composition for 5 hours. Totally 16
mg/in.sup.2 dense Pt was plated on the coupon. Next the dense
Pt-plated coupon was put in a solution consisting of
Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt), 0.2 wt %
N.sub.2H.sub.4H.sub.2O and 1.0 wt % polystyrene microsphere (1.7
.mu.m) for 7 hours at room temperature. After that, the Pt plated
coupon was put in a new Pt plating solution with microsphere for 10
hours. The coupon was then cleaned and calcined at 500.degree. C.
for 1 h in air. 16 mg/in.sup.2 porous Pt was plated on the
coupon.
[0046] Catalyst coupon was tested in a two inch long microreactor.
The reactor is made from a 0.5'' OD alloy 617 rod which is 2''
long. A slot sized 0.377''.times.0.021''.times.2'' was cut at the
center to fit the catalyst coupon and another slot adjacent to the
insert is EDM (electro discharge machining) wire cut at
0.335''.times.0.01''.times.2'' for reactant gases to flow by the
catalyst insert. The microreactor was aluminized and heat-treated
prior to catalyst coupon loading. The catalyst was tested under the
conditions of 3.2 ms contact time, 0.6% CH.sub.4, 2.0% CO, 4.3%
O.sub.2, 14.5% H.sub.2O and balance N.sub.2. At 850.degree. C., the
initial CH.sub.4 conversion was 67% and CO conversion was 100%.
After 1700 hours on stream, CH.sub.4 conversion was increased to
77% and CO conversion was kept at 100%. No deactivation was
observed during the testing period.
EXAMPLE 6--COMPARATIVE EXAMPLE
[0047] An aluminized Inconel 617 coupon was heat-treated at
1050.degree. C. for 10 hours prior to use. The surface of the
coupon was covered with an .alpha.--Al.sub.2O.sub.3 scale. The
coupon was put in a solution consisting of
Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt) and 0.2 wt %
N.sub.2H.sub.4H.sub.2O. The plating was performed at room
temperature for 18 hours. The Pt loading was 18.0 mg/in.sup.2. The
Pt plated coupon was then put in a solution consisting of
Pt(NH.sub.3).sub.4(OH).sub.2, (0.2 wt % Pt), 0.2 wt %
N.sub.2H.sub.4H.sub.2O and 1.0 wt % poly vinyl alcohol (PVA, Alfa
Aesar) for 20 hours at room temperature. The plating process was
repeated once. The coupon was cleaned and calcined at 500.degree.
C. for 1 h in air. An additional 9 mg/in.sup.2 Pt is plated on the
coupon. However, SEM micrograph shows that the surface Pt layer was
not porous (FIG. 5), which is different from Example 3.
EXAMPLE 7--MORPHOLOGY AFTER HEAT TREATMENT
[0048] The porous structure obtained in Example 3 was subjected to
additional heat treatment. As can be seen in FIG. 7, the large pore
morphology remains present after heat treatment.
DISCUSSION OF RESULTS
[0049] A total of 8 types of polymer were tried as the pore forming
material including the conventional pore formers polyvinylalcohol
(PVA), polyester and P123 (poly(ethylene oxide)-poly(propylene
oxide)-poly(ethylene oxide) triblock copolymer). Of these, only
polystyrene beads (obtained from Bangs Labs, particle diameter=1.75
.mu.m, suspension pH=7.4) formed a porous Pt layer with dispersed
pores. Data is presented in the following table:
TABLE-US-00001 Particle Materials Surface dispersed diameter
Density group Supplier pores Material (.mu.m) (g/cm.sup.3) Surface
group density Bangs Y Polystyrene 1.75 1.06 --COOH--SO.sub.4 0.013
mmol/g Labs polymer Bangs N Polystyrene 0.35 1.06 --COOH--SO.sub.4
Labs Alfa N Polystyrene 0.34 1.06 --COOH--SO.sub.4 Aesar Fluka N
Melamine Resin 2.0 1.51 -- Fluka N Polymethacrylate 1.0 1.22 --
Fluka N Melamine Resin 3.0 1.51 --COOH 0.01 mmol/g polymer
[0050] While the invention is not limited to a particular
mechanism, based on our experiments, we can propose the following
explanation. The deposition of microspheres is a complicated
process. The microspheres are constantly moving in the plating
solution due to Brownian motion. As they move, they can collide
with each other as well as with the substrate. The frequency of
collision depends on the concentration of the microspheres and how
fast the microspheres move. For the same weight concentration (e.g.
1% in our experiment), smaller microspheres have a higher number
concentration. In addition, smaller and lighter particles move
faster than larger and heavier particles. Therefore, smaller and
lighter particles collide more often. If at each collision the
microspheres attach to their target, we can expect that smaller and
lighter particles deposit faster. To produce a porous platinum
layer (with well-dispersed large pores) on a surface, we need to
deposit both platinum and polymer microspheres onto the surface at
similar rates. If platinum plates faster than the microspheres
deposit, we can only have a dense platinum layer. If the platinum
plates slower, we may have little or no platinum coating on the
substrate because the substrate is completely covered by the
polymer.
[0051] In view of the complexities, it is surprising that we
obtained a metal coating with well-dispersed polymer spheres. It is
also surprising that the deposition appears relatively unaffected
by gravity. In preferred embodiments, surfaces of a microchannel
are coated with a porous metal coating that varies by 50% or less
(deviation from thickness averaged over all coated surfaces), more
preferably varies by 20% or less, regardless of gravity, in a
device that is stationary during the coating process. Preferably,
the polymer is in the form of microspheres, preferably these
microspheres are in the size range of 1.4 to 2.0 micrometers
(.mu.m), more preferably 1.6 to 1.9 .mu.m. Preferably, the metal
comprises Pt. In some preferred embodiments, the density of the
polymer is in the range of 0.90 to 1.20 g/cc, in some embodiments
1.00 to 1.10 g/cc.
[0052] In view of the teachings and examples described herein, it
is possible, through no more than routine experimentation, to
obtain porous metal coatings (obtained through electroless plating)
with well dispersed large pores of a desired shape (preferably
spherical pores). It is believed that these coatings are superior
to coatings that could be obtained from other processes such as
Raney metals and deposition from colloidal metal solutions.
Electroless Plating Modified With Blocking Agents
[0053] Improved electroless coatings can be made with a modified
plating technique that requires at least 3 steps: (1) electrolessly
plating metal onto a surface; (2) attaching a blocking ligand to
the electrolessly plated metal; and (3) electrolessly plating the
same or a different metal onto the material from step (2). These
steps can be repeated as many times as desired. Optionally, the
blocking ligand can be removed. The blocking ligand can be removed
either before or after step (3). Also, optionally, a structure
stabilizing material can be added to maintain high surface area
during sintering and/or during use (which would typically be
conducted at elevated temperature). This modification can be
conducted with any electroless metals, as previously described.
This process can be used to selectively block certain areas such as
selected channels in a device while permitting continued
electroless plating in other areas.
[0054] The ligand can be any ligand that is known in the art to
bind to low valent or zero valent metals. Desirable blocking
ligands are those that are bonded to the metals more strongly than
solvents or other materials with which the surface may be treated,
but can still be removed by thermal or chemical methods without
damaging the electroless coating. One preferred ligand is CO. In
some preferred embodiments, the ligand comprises an anchoring
functionality such as amine, acetate, thiol, ether, phosphate,
phosphine, acyl, thiocarbonyl, etc. The blocking can be, for
example, steric; by blocking the most reactive parts of the metal
particles; or by creating a hydrophobic surface selectively over
the metal surfaces.
[0055] The blocking ligand can be removed by appropriate treatment.
For example, CO on Pt could be removed by heating (for example to
900.degree. C.) in an inert atmosphere or dilute H.sub.2.
[0056] The structure stabilizing material is preferably an oxide
that forms a thin coat and densifies to a robust structure capable
of resisting sintering. Examples include alumina sol, colloidal
alumina, silica sol, titania sol, metal alkoxide (such as silicon
or titanium alkoxide), or other precursor to a metal oxide.
* * * * *