U.S. patent application number 09/899900 was filed with the patent office on 2002-01-17 for promoted porous catalyst.
Invention is credited to Schmidt, Stephen Raymond.
Application Number | 20020006862 09/899900 |
Document ID | / |
Family ID | 23185118 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020006862 |
Kind Code |
A1 |
Schmidt, Stephen Raymond |
January 17, 2002 |
Promoted porous catalyst
Abstract
A novel precious metal doped porous metal catalyst is disclosed.
The precious metal is present in from 0.01 to 1.5 weight percent
and distributed throughout the particles of porous metal to provide
a surface to bulk ratio distribution of not greater than 60. The
present invention is further directed to a process of forming said
doped catalyst and to improved processes of catalytic hydrogenation
of organic compounds.
Inventors: |
Schmidt, Stephen Raymond;
(Silver Spring, MD) |
Correspondence
Address: |
Howard J. Troffkin
W. R. Grace & Co.-Conn.
Patent Dept.
7500 Grace Drive
Columbia
MD
21044-4098
US
|
Family ID: |
23185118 |
Appl. No.: |
09/899900 |
Filed: |
July 6, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09899900 |
Jul 6, 2001 |
|
|
|
09306398 |
May 6, 1999 |
|
|
|
Current U.S.
Class: |
502/150 ;
502/307; 502/313; 502/315; 502/316; 502/326; 564/421; 564/422;
564/423; 585/277 |
Current CPC
Class: |
Y10T 428/12181 20150115;
Y10T 428/1209 20150115; B01J 25/02 20130101; B01J 25/00 20130101;
Y10T 428/12042 20150115 |
Class at
Publication: |
502/150 ;
502/326; 502/313; 502/315; 502/316; 502/307; 585/277; 564/421;
564/422; 564/423 |
International
Class: |
B01J 023/70; C07C
005/02; C07C 209/00 |
Claims
1. A product comprising a porous particulate metal material
comprising a base metal having from about 0.01 to about 1.5 weight
percent of a precious transition metal coated on the surface of
said base metal and distributed throughout said particulate
material to have a S/B ratio of less than 60.
2. The product of claim 1 wherein the precious transition metal is
selected from Ru, Rh, Re, Pd, Pt, Os, Ir or mixtures thereof and
said base metal is selected from Ni, Co, Cu, Fe or mixtures
thereof.
3. The product of claim 2 wherein the precious transition metal is
selected from Pt or Pd or mixtures thereof and the base metal is
selected from nickel, cobalt or mixtures thereof.
4. The product of claim I wherein the porous particulate metal
material comprises at least 85 weight percent of a base metal
selected from Ni, Co, Cu or Fe or mixtures thereof and further
comprises up to 15 weight percent of aluminum, molybdenum,
chromium, iron, copper, tin, zirconium, zinc, titanium, vanadium or
mixtures thereof.
5. The product of claim 1 wherein the porous particulate metal
material further has up to about 3 weight percent of a metal
selected from the group consisting of molybdenum, chromium,
zirconium, zinc, titanium, vanadium, iron or mixtures thereof on
the surface of said base metal material.
6. The product of claim 2 wherein the promoter precious metal is
present in from 0.05 to 1 weight percent and the S/B ratio is from
about 10 to 50.
7. The product of claim 3 wherein the promoter precious metal is
present in from 0.05 to 1 weight percent and the S/B ratio is from
about 10 to 50.
8. The product of claim 4 wherein the promoter precious metal is
present in from 0.05 to 1 weight percent and the S/B ratio is from
about 10 to 50.
9. The product of claim 5 wherein the promoter precious metal is
present in from 0.05 to 1 weight percent and the S/B ratio is from
about 10 to 50.
10. The product of claim 2 wherein the porous particulate base
metal material has an average particle diameter of less than 500
microns and a surface area of at least 10 m.sup.2/g.
11. The product of claim 3 wherein the porous particulate base
metal material has an average particle diameter of less than 500
microns and a surface area of at least 10 m.sup.2/g.
12. The product of claim 10 wherein the porous particulate base
metal material has an average particle diameter of less than 75
microns and a surface area of at least 10 m.sup.2/g.
13. The product of claim 11 wherein the porous particulate base
metal material has an average particle diameter of less than 75
microns and a surface area of at least 10 m.sup.2/g.
14. The product of claim 1 wherein the porous particulate base
metal material has a particle diameter range of from 0.1 to 0.8 cm
and a surface area of at least 10 m.sup.2/g.
15. The product of claim 2 wherein the porous particulate base
metal material has a particle diameter range of from 0.1 to 0.8 cm
and a surface area of at least 10 m.sup.2/g.
16. The product of claim 2 wherein the S/B ratio is from about 10
to about 40.
17. The product of claim 3 wherein the S/B ratio is from about 10
to about 40.
18. The product of claim 1 wherein the porous particulate base
metal material has a surface area of from 20 to 150 m.sup.2/gm; the
promoter precious metal is selected from Pt or Pd or mixtures
thereof; the amount of promoter precious metal in the product is
from 0.05 to 1 weight percent; and the S/B ratio is from about 10
to 40.
19. The product of claim 2 wherein the porous particulate base
metal material has a surface area of from 20 to 150 m .sup.2/gm;
the promoter precious metal is selected from Pt or Pd or mixtures
thereof; the amount of promoter precious metal in the product is
from 0.05 to 1 weight percent; and the S/B ratio is from about 10
to 40.
20. The product of claim 4 wherein the porous particulate base
metal material has a surface area of from 20 to 150 m.sup.2/gm; the
promoter precious metal is selected from Pt or Pd or mixtures
thereof; the amount of promoter metal in the product is from 0.05
to 1 weight percent; and the S/B ratio is from about 10 to 40.
21. The product of claim 5 wherein the porous particulate base
metal material has a surface area of from 20 to 150 m.sup.2/gm; the
promoter precious metal is selected from Pt or Pd or mixtures
thereof; the amount of promoter precious metal in the product is
from 0.05 to 1 weight percent; and the S/B ratio is from about 10
to 40.
22. A hydrogenation catalyst formed by contacting an aqueous
alkaline slurry of porous particulate material comprising a base
metal with an alkaline solution of an alkaline promoter precious
metal salt represented by the formula A.sub.xMY.sub.y wherein A
represents a cation or ligand selected from ammonia, ammonium,
alkali metal or mixtures thereof, M represents a precious
transition metal atom selected from Pt, Pd, Re, Ru, Rh, Ir or Os or
mixtures thereof, Y is an anion selected from halide, nitrate,
hydroxide, carbonate, bicarbonate, sulfate, or a C.sub.1-C.sub.4
carboxylate, and x and y each independently represent an integer of
from 1 to 6; causing said porous metal material and an effective
amount of salt to remain in contact at a pH of from about 8 to 12
for a sufficient time to have from 0.01 to about 1.5 wt. percent,
based on the catalyst, of said promoter precious metal M deposit on
a portion of the surface of said porous metal material; and washing
said treated porous metal material with an aqueous solution to
lower the pH at least 0.25 unit below the contact pH or with 25
parts of solution per part of solid treated porous metal material
or both.
23. A hydrogenation reduction catalyst formed by contacting an
aqueous alkaline slurry of porous particulate material comprising a
base metal with an alkaline solution of an alkaline promoter
precious metal salt represented by the formula A.sub.xMY.sub.y
wherein A represents a cation or ligand selected from ammonia,
ammonium, alkali metal or mixtures thereof, M represents a precious
transition metal atom selected from Pt, Pd, Re, Ru, Rh, Ir or Os or
mixtures thereof, Y is an anion selected from halide, nitrate,
hydroxide, carbonate, bicarbonate, sulfate, or a C.sub.1-C.sub.4
carboxylate, and x and y each independently represent an integer of
from 1 to 6; causing said porous metal material and an effective
amount of salt to remain in contact at a pH of from about 8 to 12
for a sufficient time to have from 0.01 to about 1.5 weight
percent, based on the catalyst, of said promoter precious metal M
deposit on a portion of the surface of said porous metal material;
and retaining the product of said promoter precious metal
containing porous metal material in a water or water/alcohol slurry
for at least about 12 hours.
24. The catalyst of claim 22 wherein the base metal is selected
from Ni, Co, Cu, Fe, or mixtures thereof.
25. The catalyst of claim 23 wherein the base metal is selected
from Ni, Co, Cu, Fe, or mixtures thereof.
26. The catalyst of claim 22 wherein said M is selected from
palladium or platinum or mixtures thereof and said base metal is
nickel.
27. The catalyst of claim 23 wherein said M is selected from
palladium or platinum or mixtures thereof and said base metal is
nickel.
28. The catalyst of claim 22 wherein said aqueous slurry of base
metal particulate material has a pH of from 8 to 12 and said salt
solution has a pH of from 8 to 12 and wherein the formed catalyst
has from 0.05 to 1 wt. percent of promoter precious metal deposited
on a portion of the surface of the material.
29. The catalyst of claim 23 wherein said aqueous slurry of base
metal particulate material has a pH of from 8 to 12 and said salt
solution has a pH of from 8 to 12 and wherein the formed catalyst
has from 0.05 to 1 wt. percent of promoter precious metal deposited
on a portion of the surface of the base metal material.
30. The catalyst of claim 28 wherein the base metal particulate
material and salt are contacted at a pH of from 10 to 11.5.
31. The catalyst of claim 29 wherein the base metal particulate
material and salt are contacted at a pH of from 10 to 11.5.
32. The catalyst of claim 22 wherein the catalyst product has a S/B
ratio of from about 10 to 50.
33. The catalyst of claim 23 wherein the catalyst product has a S/B
ratio of from about 10 to 50.
34. The catalyst of claim 28 wherein the S/B ratio is from about 10
to about 40.
35. The catalyst of claim 29 wherein the S/B ratio is from about 10
to about 40.
36. The catalyst of claim 28 wherein the product is formed from a
porous base metal material having a surface area of from 20 to 150
m.sup.2/gm; the promoter precious metal is selected from Pt or Pd
or mixtures thereof; the amount of promoter precious metal in the
product is from 0.05 to 1 weight percent; and the S/B ratio is from
about 10 to about 40.
37. The catalyst of claim 29 wherein the product is formed from a
porous base metal material having a surface area of from 20 to 150
m.sup.2/gm; the promoter precious metal is selected from Pt or Pd
or mixtures thereof; the amount of promoter precious metal in the
product is from 0.05 to 1 weight percent; and the S/B ratio is from
about 10 to about 40.
38. A catalytic hydrogenation process comprising contacting an
organic compound having at least one group capable of undergoing
reaction with hydrogen in the presence of a catalyst selected from
the products of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, 15, 16or 17.
39. The process of claim 38 wherein said group is selected from
ethylenic unsaturation, acetylenic unsaturation, oxygen or sulfur
atoms of ring systems, carboxyl, carbonyl, nitrites, amides,
oximes, ketimines, nitroso, nitro, azo, azoxy, imines, alcohols,
ethers or oxides group.
40. The process of claim 38 wherein the organic compound is
selected from nitroaromatic or dinitroaromatic compounds or
mixtures thereof.
41. A process of forming a hydrogenation catalyst comprising:
contacting an aqueous alkaline slurry of porous metal particulate
material comprising a base metal with an alkaline solution of an
alkaline promoter precious metal salt represented by the formula
A.sub.xMY.sub.Y wherein A represents a cation or ligand selected
from ammonia, ammonium, alkali metal or mixtures thereof, M
represents a promoter precious metal atom selected from Pt, Pd, Re,
Ru, Rh, Ir or Os or mixtures thereof, Y is an anion selected from
halide, nitrate, hydroxide, carbonate, bicarbonate, sulfate, or a
C.sub.1-C.sub.4 carboxylate, and x and y each independently
represent an integer of from 1 to 6; causing said porous base metal
material and an effective amount of salt to remain in contact at a
pH of from about 8 to 12 for a sufficient time to have from 0.01 to
about 1.5 wt. percent, based on the catalyst, of said promoter
precious metal M deposit on a portion of the surface of said porous
base metal material; and washing said treated porous base metal
material with an aqueous solution to lower the pH at least 0.25
unit below the contact pH or with 25 parts of solution per part of
solid treated porous base metal material or both.
42. A process of forming a hydrogenation catalyst comprising;
contacting an aqueous alkaline slurry of porous base metal
particulate material comprising a base metal with an alkaline
solution of an alkaline promoter precious metal salt represented by
the formula A,MYY wherein A represents a cation or ligand selected
from ammonia, ammonium, alkali metal or mixtures thereof, M
represents a promoter precious metal atom selected from Pt, Pd, Re,
Ru, Rh, Ir or Os or mixtures thereof, Y is an anion selected from
halide, nitrate, hydroxide, carbonate, bicarbonate, sulfate, or a
C.sub.1-C.sub.4 carboxylate, and x and y each independently
represent an integer of from 1 to 6; causing said porous base metal
material and an effective amount of salt to remain in contact at a
pH of from about 8 to 12 for a sufficient time to have from 0.01 to
about 1.5 weight percent, based on the catalyst, of said promoter
precious metal M deposit on a portion of the surface of said porous
base metal material; and retaining the product of said precious
transition metal containing porous base metal material in a water
or water/alcohol slurry for at least about 12 hours.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is directed to a new catalyst product
and to a process of reducing organic compounds using said product.
More specifically, the present invention is directed to porous base
metal catalyst product having at least one precious transition
metal dopant distributed on the surface area of the catalyst such
that the surface to bulk ratio of dopant has a distinctly low
value, as fully described herein below. The present doped catalyst
product has been found to exhibit high catalytic activity and
extended catalytic life compared to previously achieved values.
[0002] Hydrogenation catalysts based on highly porous nickel
materials are well known. Such materials are part of a family of
metal alloy derived products sold by W. R. Grace & Co.-Conn.
under the trademark "Raney.RTM.". These porous materials, when
microscopically viewed, take on a sponge-like appearance having
tortuous pore channels throughout the nickel metal particle. Thus,
such materials are generically viewed as porous or spongy metal
alloy products. The metal alloy is generally composed of a major
amount of a base metal selected from nickel, cobalt or copper with
minor amounts of aluminum and other metals such as iron, chromium
or molybdenum, as deemed appropriate for a particular application.
The porous base metal catalyst product is normally referred to in
terms of the metal which is the major component of the spongy metal
product. These high surface area products have been found to have
sites for hydrogen activation and, thus, exhibit catalytic activity
when used in hydrogen reduction reactions.
[0003] It is known that the activity of spongy base metal catalysts
can be enhanced ("promoted") by the incorporation of small amounts
of certain transition metals. For example, French Patent 913,997
proposed incorporating chromium in up to 3.5 percent based on the
content of nickel present in a Raney nickel catalyst. Promotion of
catalysts was initially accomplished using transition metal
elements which are readily available commodity metals, such as
iron, molybdenum or chromium. These metals could be used in large
amounts without causing a detrimental economic limitation to their
commercial usefulness.
[0004] In general, porous base metal catalysts, such as porous
nickel catalysts are formed by first producing a base
metal-aluminum (preferred) or base metal-silicon alloy using
conventional metallurgical techniques. The formed alloy is ground
into a fine powder and classified by passing it through a sieve to
provide a material having a desired particle size which is normally
less than 500 microns and, preferably less than 75 microns. Larger
particles are recycled for further grinding.
[0005] The alloy powder is then treated with a base to leach out a
substantial amount of the aluminum metal or silica present. The
base may be selected from either an inorganic (preferred) or
organic compound. For example, in conventional processes an aqueous
solution having from about 5 to 50 weight percent concentration of
an alkali metal hydroxide (e.g., sodium hydroxide) is employed as
the leaching agent. The treatment of the alloy is usually carried
out at elevated temperatures of from about 40.degree. C. to
110.degree. C. The alloy powder can be directly added to the alkali
solution or it can be formed into an aqueous suspension which is
then contacted with the alkali solution. The aluminum contained in
the alloy dissolves to form an alkali metal aluminate (e.g., sodium
aluminate) with vigorous evolution of hydrogen. When silicon is in
the alloy, the base forms the corresponding alkali metal silicate.
The powder and alkali are normally allowed to remain in contact
with each other for several hours at elevated temperature (e.g.,
40.degree.-110.degree. C.) until the aluminum (or silicon) content
is reduced to the desired level. The crude porous catalyst is
separated from the reaction liquor and then conventionally washed
with water until the wash water has a slightly alkaline pH value of
about 8. The pore volume, pore size and surface area of the leached
alloy will depend upon the amount of aluminum (or silicon) in the
initial alloy and the degree of leaching. The nature of the
porosity of the resultant base metal catalyst is one of tortuous
pores throughout the volume of the catalyst particle. The resultant
product normally has a pore volume (BET) of from about 0.05 to
about 0.3 cc/g; an average pore diameter ranging from about 50 to
500 Angstroms; and a surface area (BET) of at least 10 m.sup.2/g,
preferably ranging from about 20 to about 150 m.sup.2/g.
[0006] The resultant porous base metal product has been used as a
hydrogenation catalyst to cause reduction of organic compounds,
such as, for example, nitroorganics, to their corresponding amine
compound. In order to further enhance the catalytic properties of
such porous products, the addition of promoter metals, such as
Group VIII transition metals (e.g., iron or chromium), has been
previously accomplished by (i) adding the promoter metal to the
base metal and aluminum (or silicon) when metallurgically producing
the initial alloy; (ii) adding a salt of the promoter metal to the
alkali leaching solution; or (iii) contacting the leached or
leached and washed porous base metal catalyst with a salt solution
of the promoter metal.
[0007] The process of adding promoter metal to the base metal
during alloy formation, as disclosed in U.S. Pat. 3,781,227, has
certain limitations. Firstly, it can be envisioned that some of the
promoter metal is "encapsulated" in the solid body or skeleton of
the base metal and not on the surface area of the resultant
catalyst. In this form, the promoter metal does not cause a direct
enhancement of the hydrogenation catalyst sites which are located
on the surface area of the highly porous material. Further, a
portion of the promoter metal may be removed during any one or all
of the steps required to form the porous alloy. Thus, large amounts
of a promoter metal are normally added during alloy formation to
compensate for any loss during processing and through
encapsulation. Because of the possible loss of promoter metal
during processing and the inefficiency of encapsulated promoter
metal, the alloy-addition method is not considered appropriate when
the metal is a costly transition metal, such as platinum,
palladium, osmium, ruthenium or the like.
[0008] Alternately, promoter metals have been added to the alkali
leaching solution (see Great Britain Pat. 1,119,512 and U.S. Pat.
3,326,725) in attempts to enhance resultant porous nickel's
catalytic activity. The leaching solution is normally an alkaline
aqueous or aqueous-alcoholic solution. In general, the promoter
metal is introduced as an acid salt, such as a halide salt. In most
instances, the leach solution does not maintain the promoter metal
in solution but, instead, causes it to plate out on the outer shell
of the porous base metal particle. Thus, the resultant porous
particle has the promoter metal located on only a small fraction of
the particle's surface area.
[0009] Spongy nickel or other base metal catalysts which have been
previously formed and washed by conventional processes have been
subjected to dopant metals just prior to use, in attempts to
promote its catalytic activity. The dopant metal is normally
introduced as an aqueous or aqueous/alcoholic solution of an acid
salt, such as PtCl.sub.4, PdCl.sub.2, H.sub.2PtCl.sub.6 or the
like. In JACS 71 1515 (1949) and JACS 72 1190 (1950) Levering et
al. disclosed the addition of an organic tertiary amine to the acid
salt dopant solution. These authors taught that one should use the
doped spongy metal product immediately after the addition of dopant
(without further washing), in order to achieve enhanced catalytic
performance. Such products exhibited only slight increase in
catalyst activity and substantially no improvement in their active
catalyst life.
[0010] It is highly desired to provide a promoted porous base metal
catalyst (e.g., Raney.RTM. nickel) which exhibits high catalytic
activity after storage (maintains good initial activity) and
extended catalyst life during use (exhibits slow or delayed
deactivation). Further, it is desired to provide a promoted base
metal catalyst which has a precious transition metal as its
promoter metal and said precious transition metal is substantially
uniformly distributed as a coating on the surface area of the
porous metal catalyst. Thus, the precious transition metal is
substantially uniformly distributed across the particle diameter of
said catalyst. Still further, it is desired to provide a precious
transition metal promoted porous base metal catalyst wherein said
promoter metal is present in up to about 1.5 percent by weight and
the promoter metal's surface to bulk ratio (as defined herein
below) is less than 60.
SUMMARY OF THE INVENTION
[0011] The present invention provides a novel transition metal
promoted porous base metal catalyst. The transition metal is
present in from 0.01 to about 1.5 percent by weight, and is
distributed throughout the surface area of said porous catalyst so
as to have a surface to bulk distribution of not greater than 60.
The present invention further provides a novel method of forming
said precious transition metal promoted porous base metal catalyst.
Finally, the present invention provides an improved process for
hydrogenation of organic compounds utilizing said catalyst.
DETAILED DESCRIPTION
[0012] The following defined terms are used in this specification
and appended claims:
[0013] "Base metal" refers to metals of iron, nickel, cobalt,
copper and mixtures thereof which are used to form porous or spongy
metal catalyst products. These metals may be combined (e.g.,
alloyed) with minor amounts of other metals (e.g., chromium,
titanium, molybdenum, zinc, zirconium, aluminum) as an alloy or
co-deposited coating. When more than one base metal is present in
the spongy metal catalyst, all of said base metals shall be
included in determining the S/B ratio, as defined below. The
preferred base metals are nickel and cobalt and most preferably
comprises nickel alone or with minor amounts of other metals.
[0014] "Precious metal" refers herein to transition metals of
palladium, platinum, ruthenium, rhodium, rhenium, osmium, iridium
and mixtures thereof.
[0015] "Dopant metal" refers to a transition metal which is
distinct from the metals forming a porous base metal catalyst and
is present in low concentrations in the base metal catalyst to
enhance its catalytic properties (e.g., dopant precious metals, as
defined below, and may also include chromium, molybdenum, titanium,
zinc, iron, zironium or mixtures thereof).
[0016] "Dopant precious metal" and "promoter precious metal" each
refers herein to precious transition metals of Pd, Pt, Ru, Re, Rh,
Ir and Os present in small quantities on the surface area of a
porous, particulate base metal for the purpose of enhancing the
catalytic properties of said porous, particulate base metal. The
preferred dopant transition metals are those of platinum and
palladium with palladium being most preferred.
[0017] "Surface volume" refers to the outer volume or shell of a
catalyst particle of the present invention which is roughly the
outer 50 Angstroms of the particle's radius (i.e., extending from
the outer surface of the particle inward toward the center of the
particle by about 50 Angstroms).
[0018] "Surface dopant concentration" refers to the atomic ratio of
dopant metal to base metal within the surface volume of a catalyst
particle.
[0019] "Bulk dopant concentration" refers to the atomic ratio of
dopant metal to base metal for the entire catalyst particle.
[0020] "Surface to Bulk Ratio" or "S/B" in respect to a porous base
metal catalyst product, refers to ratio of surface dopant
concentration to bulk dopant concentration.
[0021] The present invention is directed to a novel hydrogenation
catalyst product based on a porous base metal catalyst which has up
to about 1.5 weight percent of a precious transition metal selected
from palladium, platinum, rhodium, ruthenium, rhenium, iridium or
osmium or mixtures thereof coated on the surface area of said
catalyst and having said precious transition metal of sufficiently
low concentration in the particle's surface volume to provide a
surface to bulk ratio, S/B, of less than 60. The present catalyst
is particularly useful in reducing nitroaromatics to their
respective amine derivatives.
[0022] The present catalyst is based on porous, particulate base
metal catalyst product, preferably a nickel metal (e.g., Raney.RTM.
nickel) product. The present invention shall be described by using
a porous, particulate base metal product wherein the base metal is
composed of nickel. It is to be understood that other porous,
particulate base metal products (Co, Cu, Fe) can be substituted and
used to form the present improved catalyst and the process of
hydrogenation using the same.
[0023] The porous base metal (e.g., nickel) catalyst product is
formed by conventional techniques. For example, a nickel/aluminum
alloy is initially formed by a pyrometallurgical process to provide
an alloy having from about 30 to 60 (preferably from about 42 to
56) weight percent nickel and from about 70 to 40 (preferably from
about 58 to 44) weight percent aluminum. Small amounts of other
base metals may, optionally, be present. The alloy is crushed and
ground into particles having an average particle size of less than
500 micron diameter, preferably less than 75 micron diameter. The
powder product is activated by leaching the aluminum from the alloy
with an alkali solution, such as an aqueous solution of sodium
hydroxide (preferred) or potassium hydroxide. The alkali is used at
concentrations of greater than about 15 weight percent, preferably
from 15 to 35 and most preferably from 20 to 35 weight percent. The
leaching can be carried out at ambient temperature but preferably
is conducted at elevated temperatures which can be as high as the
boiling point of the leaching solution. Temperatures of from about
40.degree. to 110.degree. C.(preferably 60.degree. to 100.degree.
C.) are suitable to cause substantial rate of leaching and removal
of the aluminum metal from the alloy. When the present catalyst is
contemplated for use in fixed bed reactors, the porous, particulate
base metal product may have an average particle size diameter (or
largest dimension) of from about 0.1 to 0.8 cm. The alloy is
leached with an alkali solution described above having an alkali
concentration of from about 5 to 35 weight percent, preferably from
about 5 to 20 weight percent. The leaching is normally carried out
at elevated temperatures of from about 30.degree. to about
900.degree. C., preferably from about 30.degree. to 50.degree.
C.
[0024] The resultant porous particulate catalyst product is
composed of base metal, such as nickel and, optionally, minor
amounts (up to about 15 wt. percent preferably up to about 12 wt.
percent) of other transition metals as well as residual aluminum.
It is to be understood that the term "base metal" and the like used
to described and define the spongy metal catalyst herein and in the
appended claims shall mean (unless specifically stated otherwise) a
metal product composed of a major amount (at least about 85 wt.
percent) of a single base metal or a mixture of base metals
(normally one base metal is in majority) which has a minor amount
(up to about 15 wt. percent, preferably up to about 12 wt. percent)
of other metal(s) such as chromium, titanium, molybdenum, zinc,
zirconium or mixtures thereof as well as with residual aluminum.
The product has a high degree of tortuous pores throughout each of
the particles to provide a high surface area porous particulate
catalyst product. This product is washed with water to remove the
aluminate by-product. Total removal of the aluminate is not
required. The washing is conducted with water having a temperature
of from ambient to about 60.degree. C., preferably between 30 and
45.degree. C. It is preferred that the washing be conducted under
an inert (e.g., N.sub.2 or Ar) atmosphere or one having a dilute
concentration (2-8%, preferably 3-5%) of hydrogen. The resultant
particulate product normally has a pore volume (Nitrogen-BET) of
from about 0.05 to about 0.3 cc/g; an average pore diameter ranging
from about 50 to 500 Angstroms; a surface area (BET) of at least 10
m.sup.2/g and preferably ranging from about 20 to about 150
m.sup.2/g; and an average particle diameter of less than 500
microns preferably of less than 75 microns or, when contemplated
for use in fixed bed reactors, of from about 0.1 to 0.8 cm.
[0025] In the instant invention washing is continued until the
effluent wash water has an alkaline pH of from at least 8 to about
12 with from 9 to 12 being preferred and from 10 to 11.5 being most
preferred. The alkalinity of the aqueous slurry containing the
porous base metal catalyst may be substantially the same as the
alkalinity of the dopant precious metal solution to be used to from
a doped catalyst, as described herein below.
[0026] The porous base metal catalyst is treated with an alkaline
solution of a basic salt of the dopant precious metal to provide
the catalyst of the present invention. The salts found useful in
providing the unique catalyst are alkaline salts represented by the
general formula (A).sub.xMY.sub.y wherein A represents a cation or
ligand selected from ammonia, ammonium, or an alkali metal such as
sodium, potassium or the like or mixtures thereof; M represents a
precious transition metal, as defined below; Y represents an anion
selected from halide, hydroxide, oxide, carbonate, bicarbonate,
nitrate, sulfate or a C.sub.1-C.sub.4 carboxylate; and x and y
represent integers of from 1 to about 6 to provide a neutral
(charge balanced) salt product. A is preferably selected from
ammonia or ammonium and most preferably selected from ammonia or if
A is an alkali metal it is preferably selected from sodium. The
salt should be soluble in water or alcohol or mixtures thereof and
cause the solution to exhibit an alkaline pH of from 8 to 12,
preferably from 9 to 11.5 and most preferably from 9.5 to 11.5.
Examples of such salts are: (NH.sub.3).sub.4PdCl.sub.2.nH.sub.2O,
(NH.sub.3).sub.4PtCl.sub- .2.nH.sub.2O
(NH.sub.3).sub.4Pd(NO.sub.3).sub.2.nH.sub.2O,
(NH.sub.3).sub.4Pt(NO.sub.3).sub.2.H.sub.2O,
[Pt(NH.sub.3).sub.4][PtCl.su- b.4], (NH.sub.3).sub.6RuCl.sub.3,
NH4ReO.sub.4, (NH.sub.3).sub.4ReO.sub.4, KReo.sub.4,NaReO.sub.4 ,
[Rh(NH.sub.3).sub.5Cl]Cl.sub.2, (NH.sub.3).sub.4PtCl.sub.2,
K.sub.2OsO.sub.4.nH.sub.2O, and the like. The symbol "n" can be an
integer of 0 to 4.
[0027] The precious transition metal (M) of the basic salt is
selected from Pd, Pt, Ru, Rh, Re, Ir and Os and mixtures thereof
with Pd and Pt being preferred and Pd being most preferred. It has
been found that the presently described precious transition metals
provide high catalytic activity and extended catalytic life when
plated in very low amounts on the surface area of a porous base
metal particulate material according to the present invention.
[0028] The porous, particulate base metal catalyst is doped with
the precious transition metal according to the present invention by
contacting an alkaline slurry of the porous base metal material
with an alkaline solution of a precious metal salt. Alternately,
one can add the solid salt directly to the affected slurry
whereupon it dissolves to form the combined alkaline solution and
slurry. The salt should be used in an amount such that the weight
concentration of dopant transition metal in the resultant doped
catalyst is from 0.01 to 1.5%, preferably from 0.05 to 1% and most
preferably from 0.1 to 0.5% by weight based on the weight of the
porous base metal catalyst. The exact amount of salt used will
depend on the degree of doping desired in the finished catalyst.
Normally, the alkaline salt should be added to water or
water-alcohol to provide a solution of salt wherein the salt
concentration is from about 5 to 40 (preferably 10-30) weight
percent.
[0029] The porous base metal catalyst may, in addition to the
precious transition metal dopant, be doped with a non-precious
metal dopant selected from iron, chromium, molybdenum, titanium,
zinc, vanadium, zirconium or mixtures thereof. They may reside as a
coating on the surface in the form of a dopant metal in its zero
valence state or in an oxidized state. These dopant metals may be
present in up to 3 weight percent (preferably from 0.2 to 3 weight
percent, most preferably from 0.5 to 2 weight percent) of dopant
metal based on the weight of the porous base metal catalyst. They
are added by conventional processes using dopant metal salt
solutions. The doped base metal catalyst must also be doped with a
dopant precious metal, as described herein.
[0030] The alkaline precious metal salt solution is contacted with
an aqueous slurry of the powder porous base metal catalyst,
previously formed as described above, for a sufficient time to
allow substantially complete plating out of the precious transition
metal onto the surface area of the base metal catalyst. The exact
length of time will depend on the particle size, and specific
porosity of base metal used, the pH of the solution and the
concentration and particular precious transition metal present.
Normally, the porous base metal catalyst and the alkaline precious
transition metal salt are maintained in contact in the slurry for
an extended period of time such as from about 10 to 60 minutes or
longer with from about 15 to 45 minutes being preferred. The
temperature at which this is conducted is not critical and can be,
for example from room temperature to about 80.degree. C. such as
from 30-45.degree. C.
[0031] The spent solution is then separated from the doped
catalyst. The doped catalyst must then be washed until the wash
solution is free of precious transition metal. The wash solution
should be an aqueous solution (preferred) or an aqueous-alcoholic
(C.sub.1-C.sub.3 alkanol) solution. During the washing a majority
of by-product salts (e.g., NH.sub.4Cl, NaCl) are removed. The
washing should continue until the solution containing the doped
catalyst has a pH of at least 0.25, preferably at least 0.5 and
most preferably at least 1 (e.g., 1.5), unit lower than the
alkaline pH at which the porous base metal catalyst and the
alkaline precious transition metal dopant salt are contacted. The
pH can be reduced by washing the doped catalyst with water or
water-alcohol solutions (preferred) and/or by the addition of an
acidic agent or a buffer agent to cause the resultant slurry to
have the desired pH. It is preferred that the aqueous suspension of
doped catalyst resulting from the washing(s) have a resultant pH of
from about 8 to 9.5, preferably 8 to 9. It is preferred that the pH
of the doping slurry be high (e.g., 9.5-12) and that the aqueous
slurry of doped catalyst is at least 1 unit lower after washing.
When the base metal catalyst and precious transition metal dopant
are contacted in an alkaline slurry having a pH of 8 to 9.5, the
product should be washed with at least 25 parts (e.g., from 25 to
100 parts) of water for each part by weight of doped catalyst
solid. The wash water may be of neutral pH or slightly alkaline by
the addition of a base such as NH.sub.4OH, NaOH or the like. The
washing can be optionally followed by an alcohol (C.sub.1-C.sub.3
alkanol) or water-alcohol wash. The resultant doped base metal
catalyst is normally stored as an aqueous slurry until use.
[0032] In addition to washing, or in lieu thereof, the doped
catalyst can be removed from the spent dopant solution and soaked
in water or an aqueous alcoholic (C.sub.1-C.sub.3 alkanol) bath for
at least 12 hours, preferably at least one day prior to use. This
aging has been found to aid in achieving a highly desired catalyst
of low S/B ratio.
[0033] It has been found that the doped catalyst product formed in
the manner described above can be stored for an extended period of
time of from one day to six months or greater prior to use without
losing its catalyst activity. In addition, the doped catalyst
product formed in the manner described above exhibits extended
catalytic active life during use when compared to conventional
catalyst products of the same material.
[0034] It is believed, though not meant to be a limitation on the
subject invention, that solutions of the present precious
transition metal salts are capable of penetrating into the pores of
the base metal catalyst wherein precious metal electrochemically
plates out when reduced by the base metal itself and/or by a
fraction of the surface hydrogen of the base metal material. In
addition, it has been found that beyond the removal of undeposited
species, the final washing and/or soaking of the precious
transition metal doped porous base metal catalyst also aids in
providing a more homogeneous or even distribution of precious
transition metal throughout the surface area of the product. The
immediate use after addition of the dopant salt does not allow the
full migration of the dopant to the interior of the particles,
while the present more time-extended process completes this
migration to a final, more stable configuration. Removal of
undeposited species by washing also makes for a chemically enhanced
product which is more compatible with a variety of hydrogenation
processes and has been shown in some processes to lead to superior
activity.
[0035] As stated previously, the doped catalyst of the present
invention is a highly porous particulate product in which the pores
are of a tortuous nature throughout each of the particles to
provide a high surface area doped catalyst product. The surface
area as used herein and in the appended claims is all areas
assessable to nitrogen and measured by the Nitrogen-BET method. The
term "surface" as used herein and in the appended claims shall be
surfaces of the tortuous pores throughout said particles and of the
particles, per se.
[0036] The presently produced precious transition metal doped
porous base metal catalyst has been found to have a more
homogeneous or even distribution of precious transition metal
throughout the surface area of each particle of the porous base
metal catalyst. This can be described in terms of the atomic ratio
of the precious transition metal to base metal as a function of the
cross-section of the catalyst particles. This distribution can be
readily measured by x-ray photoelectron spectroscopy ("XPS") or
electron spectroscopy for chemical analysis ("ESCA"). Another
technique to determine the atomic ratio of the metals is
transmission electron microscopy ("TEM"). ESCA analytical method
simultaneously measures the outer surface volume or skin to a depth
of about 50 .ANG. of a large number of particles. Thus, an atomic
ratio of dopant metal to basic metal in the surface volume of the
particles can be measured and when compared to the bulk chemical
analysis one can determine the amount of dopant enhancement at the
surface versus the overall amount of dopant. It has been found that
with respect to the present doped catalysts, the amount of dopant
enhancement in the surface volume is low and thus the amount of
dopant metal residing in the internal volume (between about 50
.ANG. to the center of a particle) is proportionately higher than
that of known doped porous catalysts. Prior known doped catalysts
are products where the dopant metal is very highly concentrated in
the outer surface volume and, conversely, the dopant metal is in a
very low concentration in its internal volume.
[0037] The ratio of surface concentration to bulk concentration of
the dopant precious metal (referred to herein after and in the
appended claims as "S/B ratio") can be readily determined by ESCA
analysis and bulk analysis of a product. The S/B ratio of the
precious transition metal doped base metal catalyst of the present
invention is less than about 60, with S/B ratios of about 10 to 50,
preferably 10 to 40 being attainable. All ratios within this range
of 10 to 60 being encompassed herein by this statement. In
contrast, porous base-metal catalysts conventionally doped with
equivalent amounts of precious metal have S/B ratios which are a
multiple factor higher. Thus, if one were to plot a concentration
of precious transition metal across the particle diameter, one
would obtain a curve less steeply peaked at the edges (outer
50.ANG.) for the presently doped catalyst product than for
conventionally formed catalyst product having the same degree of
dopant precious metal.
[0038] The subject doped catalyst, especially the preferred doped
nickel catalyst, has been found to exhibit improved catalytic
activity of from about 1.2-1.8.times.greater than the conventional
doped catalyst and over conventional doped base metal derived alloy
catalysts as shown by comparative examples herein below.
[0039] The doped catalyst product of the present invention can be
described as a porous, base-metal catalyst material. It is composed
of a major amount (up to about 85 wt %) of a base metal, e.g. Ni,
Co, Cu, or Fe, and minor amounts of up to about 15 wt. percent,
preferably up to about 12 wt. percent of other metals (than the
major base metal) selected from aluminum, chromium, iron, copper,
molybdenum, tin, zirconium, zinc, titanium, vanadium or mixtures
thereof. The porous base metal catalyst has a precious metal dopant
selected from Pt, Pd, Ru, Rh, Re, Ir, Os or mixtures thereof in up
to about 1.5 wt. percent (e.g., 0.01 to 1.5), preferably from 0.05
to 1, such as 0.1 to 0.9 and most preferably from 0.1 to 0.5 wt.
percent (and all ranges included within said range of 0.05 to 1.5
wt. percent). The dopant precious transition metal is coated on a
portion of the surface area of said porous base metal and is
distributed within the particles with respect to their diameter so
that its S/B ratio is less than 60, such as from about 5 to about
60, preferably less than 50, more preferably less than 40 and most
preferably less than 35. The lower the S/B ratio the more preferred
is the resultant catalyst.
[0040] The product of the present invention is formed by the
process of contacting a solution of an alkaline salt of the
precious transition metal which may be described by the formula
A.sub.xMY.sub.y wherein each of the symbols A, M, Y, x and y are
defined above, with an alkaline slurry of a porous base metal
catalyst. The slurry, at a pH of from 8 to 12, preferably from
about 9 to 11.5, is contacted with an alkaline salt solution, as
described above, for a period of time to allow substantially all of
the precious transition metal of the salt to become coated on and
adhered to portions of the surface area of said porous base metal
catalyst. The product of said contact is then washed until the wash
solution is essentially free of dopant metal and has a pH which is
at least 0.25 unit lower than the pH of the doping slurry.
Alternately or in addition to the pH adjustment (preferable) the
washing is conducted with at least 25 wt. parts of water for each
wt. part of solid product. The doped base metal catalyst of the
present invention is aged in an aqueous or aqueous-alcoholic
solution for at least 12 hours preferably one day prior to use. The
washed product is maintained in an aqueous or aqueous-alcoholic
bath until use.
[0041] The doped catalyst product of the subject invention is
useful as a hydrogenation catalyst. The present product has been
found to have high catalytic activity and provide extended
catalytic life when compared to conventional porous base metal
catalysts which have the same dopant. The present doped catalyst
products have S/B ratios which are substantially lower (more
uniform doping) than conventional products.
[0042] The present invention further provides for improved
catalytic hydrogenation reduction processes conducted in the
presence of the above-described doped catalyst. Said processes
include all hydrogenation reactions which are carried out with
porous base metal catalysts, such as Raney.RTM. nickel catalysts.
Examples of such reactions are described in Skeleton Catalysts in
Organic Chemistry by B. M. Bogoslawski and S. S. Kaskowa and in Use
of Nickel Skeleton Catalysts in Organic Chemistry VEB Deutsches
Verlag der Wissenschaften, Berlin 1960 Pg. 40-124, the teachings of
which are incorporated herein in their entirety by reference.
[0043] Accordingly, for example, the metal catalysts prepared
according to the invention can be employed for the hydrogenation of
unsaturated hydrocarbons with an ethylenic and/or triple bond, or
of diene systems, of aromatic compounds, such as, for example,
benzene, naphthalene, diphenyl and their derivatives, or of
anthraquinone and phenanthrene, of heterocyclic compounds with
nitrogen, oxygen or sulfur atoms in the ring system, of carbonyl
groups, of carboxyl groups or their esters, of carbon-nitrogen
compounds, such as, for example, nitrites, acid amides, oximes and
ketimines, of unsaturated compounds containing halogen, sulfur,
nitroso and nitro groups, of azo and azoxy compounds, of
hydrazines, Schiff's bases, imines and amines, of carbon-oxygen
compounds, such as, for example, alcohols, ethers, ethylene oxides
and organic peroxides and ozonides, of carbon-carbon compounds and
of nitrogen-nitrogen compounds.
[0044] The doped catalysts prepared according to the invention are
preferably used for the hydrogenation of nitroso and nitro
derivatives of aromatic compounds, unsaturated hydrocarbons, and
nitrites. For example, nitrobenzene and nitrotoluene as well as
dinitrobenzene and dinitrotoluene can be readily reduced to their
corresponding primary amine derivative by contacting the nitro
aromatic compound with hydrogen in the presence of the doped
catalyst of the present invention. The reactions can be carried out
at ambient temperature and pressure or at elevated temperatures of
up to about 175.degree. C., preferably between about 60.degree. C.
and 150.degree. C. The reactions can be carried out at pressures of
up to about 1000 psig with preferred pressures being from about 100
to about 500 psig. It has been unexpectedly found that the present
doped catalyst provides very high degree of enhanced reactivity
when used under elevated temperature and pressure conditions. Thus,
conditions of temperature of from about 130 to 175.degree. C. and
pressures of from 300 to 500 psig are preferred. The use of the
doped catalyst of the present invention is exemplified herein by
illustration of hydrogenation reduction of para-nitrotoluene.
[0045] The hydrogenation may be carried out in a continuous sump
phase hydrogenation apparatus, which consists of a number of
reactors of customary construction connected in series, with the
aid of which a hydrogen cycle is produced. Other conventional batch
and continuous apparatus may be used. The catalyst of the present
invention can be suspended in an aqueous-alcoholic mixture (e.g., a
C.sub.1-C.sub.3 alkanol). Alternately, the catalyst may be of a
fixed bed type (larger particle size of from about 0.1 to 0.8 cm)
used in a packed bed reactor with either a liquid or vapor phase
reaction mixture conventionally used.
[0046] The doped catalyst of the present invention can be suspended
in the hydrogenation apparatus in an ethanol/water mixture, for
example with a mixture composed of 95% by weight of ethanol and 5%
by weight of water, as the solvent. A solution of para-nitrotoluene
in the ethanol/water mixture is formed and to it the catalyst is
added. The treatment is then carried out at elevated pressure, for
example 60 to 500 psig of hydrogen pressure, and at temperatures of
75.degree. C.-140.degree. C.
[0047] The following examples are given for illustrative purposes
only and are not meant to be a limitation on the invention as
defined by the claims appended hereto. All parts and percentages
are by weight unless otherwise indicated. Further, any range of
numbers recited in the specification or claims, such as that
representing a particular set of properties, conditions, physical
states or percentages is intended to literally incorporate
expressly herein any number falling within such range, including
any subset of numbers within any range so recited.
EXAMPLE I
Preparation of Base Metal Catalyst
[0048] A previously formed nickel-aluminum alloy composed of about
42 weight percent nickel/58 weight percent aluminum was ground into
a powder having particle size of about 30-40 microns average
diameter. The powdered alloy was intermittently added in small
portions to a 30 weight percent sodium hydroxide solution which was
preheated to 80.degree. C. prior to introduction of alloy. The
weight ratio of NaOH (solid) to Al of the alloy was about 2.7:1.
The addition was carried out at a rate of about 1000 g alloy powder
per hour. After completion of the addition of alloy powder, the
resultant slurry was maintained at 80.degree. C. with agitation for
about 4 hours.
[0049] The resultant spongy nickel catalyst was separated from the
slurry liquid by decantation followed by washing of the solid
catalyst until the spent wash solution had a pH of about 9. The
washing of the solid catalyst was carried out by cyclic addition of
water at 45.degree. C. followed by stirring, settling of solids and
decanting of the wash water.
[0050] The resultant spongy nickel metal catalyst was stored as a
50 wt. percent aqueous slurry.
EXAMPLE II
Precious Metal Doped Nickel Catalyst
[0051] A series of nickel catalysts were prepared in the same
manner as described in Example I above except that the pH of the
final wash water was varied. Separate slurries were formed with pH
of from 8 to 12 and each catalyst was then doped with a precious
metal, as described below.
[0052] Standardized aqueous solutions of Pd salts and of Pt salts
were formed. These solutions had a pH of about 9 to 10.
[0053] A series of doped catalyst were formed by introducing with
agitation a portion of a standardized precious metal salt solution
having a precious metal content of from 0.1 to 1.0 weight percent
precious metal based on the spongy nickel catalyst (solid content)
of the treated slurry. The treated slurry was maintained under
agitation for about 30 minutes. The agitation was then stopped and
the solids allowed to settle. A portion of the liquid was decanted
and analyzed for precious metal content. The analysis showed no
precious dopant metal present in the spent liquid. The slurry was
washed by cyclical water/decantation to a final pH of about 9 and
with at least 25 parts by weight of water for each part of catalyst
product. The resultant precious metal doped spongy nickel catalysts
were stored under water for at least one day prior to being tested
and used.
[0054] Table I below provides the data and description with respect
to each of the series of samples produced. This description
includes:
[0055] precious metal dopant salt (PM)
[0056] dosage of dopant in the doped catalyst (% precious metal
based on nickel of spongy catalyst)
[0057] pH of dopant solution
[0058] pH of catalyst slurry before doping treatment
[0059] pH of catalyst slurry after (post) doping treatment
[0060] bulk analysis (ICP) of doped catalyst
[0061] Surface Analysis (XPS) of doped catalyst
[0062] Surface to Bulk (S/B) Ratio
[0063] Bulk chemical analysis was analyzed by Inductive Coupled
Plasma-Atomic Emission Spectroscopy ("ICP"). Each sample was washed
with water and then completely dissolved in a mixture of
HCl/NHO.sub.3 acid (3:1) solution. The sum of the percent assays
determined was normalized to 100%. The weight percentages for
precious metal, nickel, and residual aluminum are reported in Table
I as well as the atomic ratio of precious metal to nickel.
[0064] The average precious metal dopant concentration at the doped
catalyst particles' outer shells (surface volume) was determined by
X-ray Photoelectron Spectroscopy (XPS). For each measurement, a
small sample of about 0.5 g water-wet catalyst was removed from its
slurry and dried in a U-shaped tube under flowing helium gas at a
temperature of 130.degree. C. The dried sample is then sealed in
the tube and transported to the XPS instrument. The sample was
introduced via an antechamber to the XPS instrument. XPS
measurements were carried out on a PHI 5600 ESCA system (.PHI.
Physical Electronic). The catalyst was handled under an Argon
atmosphere within an environmentally controlled glove box. Moisture
content was no higher than 0.40 ppm and oxygen content was
generally 0.00 ppm within the glove box environment.
[0065] Spectra were obtained using an aluminum x-ray source
operating at 14.8 kV/25 mA energy and the detector positioned at
45.degree. relative to the material being analyzed. Instrument
calibration was performed using a Cu reference standard after 10
minutes sputtering in Argon. Because the 2.sub.p{fraction (3/2)}
and 3.sub.p{fraction (3/2)} photoelectron peak energies of Cu are
widely separated in energy, measurement of these peak binding
energies provided a quick and simple means of checking the accuracy
of the binding energy scale.
[0066] The material was loaded as a thin layer onto double-sided
tape mounted to a 1 inch diameter stainless steel stub. The stub
was placed in an enclosed transfer vessel and mounted onto the
intro chamber of the XPS instrument. The sample was transferred in
vacuo (10.sup.-6 torr) into the main analysis chamber and further
vacuum of 10.sup.-8 to 10.sup.-9 torr was achieved. A 5 minute
surface scan to identify all detectable elements from 1-1100eV was
performed. Based on the findings from the survey, a 60 minute
detailed scan on selected elements was performed with an energy
resolution of 0.125 eV. For convenience, the spectral data were
imported into an external curve-fitting software package (MULTIPAK
v2.2a). Other conventional methods can be used. All the
curve-fitting and atomic concentration functions were performed
using this software. Sensitivity factors for each element were
automatically configured within the software and used in the atomic
concentration calculations.
[0067] The Surface/Bulk ("S/B") ratio was calculated as follows
(e.g., with Pd and Ni as dopant and base metal, respectively): 1 S
/ B ratio = surface Pd / Ni bulk Pd / Ni
[0068] which is 2 [ ( XPS Pd atom concentration / ( XPS Ni atom
concentration ) ] [ ( ICP bulk % Pd / atomic wt Pd ) / ( ICP bulk %
Ni / atomic wt . Ni ) ]
EXAMPLE III
[0069] A sample was made in the same manner as described above in
Example II for Samples 2D-2F except that the base metal catalyst
was nickel based having about 2 wt.% Fe and 2 wt.% Cr in the spongy
catalyst.
[0070] The dopant catalyst was analyzed in the same manner as
described above and the results are reported as Sample 3 in Table I
below.
1TABLE I Dopant (PM) Salt Bulk Analysis ICP Surface Vol. Ex- Target
Catalyst Slurry pH Atom PM/Ni ample Conc. Salt pH Pre-doping
Post-doping % PM % Ni % Al PM/Ni (XPS) S/B Ratio 1 -- None -- -- --
-- -- -- -- -- -- 2A .about.1% (NH.sub.3).sub.4PdCl.sub.2.H.sub.2O
9.1 11 9.6 1.17 92.9 5.6 0.00695 0.17 24 2B 0.5%
(NH.sub.3).sub.4PdCl.sub.2.H.sub.2O 9.1 11 9.6 0.53 93.9 5.3
0.00311 0.10 32 2C 0.5% (NH.sub.3).sub.4PdCl.sub.2.H.sub.2O 9.1 11
9.9 0.46 93.8 5.4 0.00270 -- -- 2D 0.25%
(NH.sub.3).sub.4PdCl.sub.2.H.sub.2O 9.1 11 9.7 0.25 94.0 5.5
0.00147 0.06 41 2E 0.25% (NH.sub.3).sub.4PdCl.sub.2.H.sub- .2O 9.1
8 9.0 0.26 94.3 5.1 0.00152 0.08 53 2F 0.25%
(NH.sub.3).sub.4PdCl.sub.2.H.sub.2O 9.1 9 8.9 0.28 93.8 5.7 0.00165
0.03 18 2G 0.25% (NH.sub.3).sub.4PdCl.sub.2.H.sub.2O 9.1 10 9.0
0.25 93.8 5.7 0.00147 0.04 27 2H 0.25%
(NH.sub.3).sub.4PdCl.sub.2.H.sub- .2O 9.1 11 10.3 0.22 92.9 6.6
0.00131 0.03 23 2I 0.25% (NH.sub.3).sub.4PdCl.sub.2.H.sub.2O 9.1 12
12. 0.27 93.5 5.9 0.00159 0.05 31 2J 0.25%
(NH.sub.3).sub.4PtCl.sub.2.H.sub.2O 8.1 11 10.9 0.27 94.3 5.1
0.00158 -- -- 2K 0.125% (NH.sub.3).sub.4PdCl.sub.2.H.sub- .2O 9.1
11 10.8 0.14 93.6 6.0 0.00083 0.02 24 3 0.25%
(NH.sub.3).sub.4PdCl.sub.2.H.sub.2O 9.1 11 11.0 0.25 89.3 10.2
0.00155 0.08 52
EXAMPLE IV
[0071] A series of catalytic hydrogenation reactions to convert
4-nitrotoluene to 4-methyl aniline were carried out using Pd doped
nickel based catalyst, as follows:
[0072] 10 parts of a selected catalyst was transferred into a
reaction flask, washed twice with 12000 parts of 95% ethanol/5%
water (Pharmco Products). Then 12000 parts of 95% ethanol
containing 500 parts of 4-nitrotoluene (Aldrich) was introduced
into the reaction flask. The reaction flask was evacuated and
filled with hydrogen gas. Stirring of the solution at 1200 rpm was
commenced when the temperature reached 75.degree. C. and the
pressure was at 60 psig. Each reaction was conducted in
duplicate.
[0073] The hydrogenation reaction was monitored using a multi-point
absorption reactor system which measured the gas uptake at constant
reaction pressure. This was accomplished by measuring the pressure
drop in a pre-calibrated ballast reservoir. The system was capable
of recording the parameters of reaction time, pressure, temperature
and pressure in ballast reservoir. These parameters were recorded
at the rate of 12 points/minute during the first 10 minutes of
reaction and then at increments of each 1 percent pressure drop in
the ballast reservoir. The data obtained were plotted versus time
and the reaction rates were calculated from the slope in the linear
portion of the hydrogen uptake. At the completion of each reaction,
aliquots of reaction solution were taken and analyzed by gas
chromatography-mass spectrometry. The only two materials identified
were the starting 4-nitrotoluene and the 4-methylaniline
product.
[0074] The results are given in Table II below.
2TABLE II Catalyst Activity 4-nitrotoluene conversion at 75.degree.
C./60 psig Base Catalyst Cat. Activity rate Sample Pd* wt. %
predoped pH mmol H.sub.2/min-g catalyst 2E 0.25 8 57 2F 0.25 9 77
2G 0.25 10 77 2H 0.25 11 85 2I 0.25 12 62 2J 0.50 11 73 2K 0.125 11
66 *source of Pd was (NH.sub.3).sub.4PdCl.sub.2.H.sub.2O
EXAMPLE V
[0075] A series of hydrogenation reactions of 4-nitrotoluene was
conducted using different combinations of temperature and pressure
conditions (a matrix of Temp/Pressure combinations using 200 and
400 psig and 125.degree. C. and 140.degree. C.). The catalyst used
was palladium doped nickel based catalyst (2G) described in Example
II above.
[0076] Each of the hydrogenation reactions were conducted using a
Bench Top EZE Seal Reactor (Autoclave Engineers) which is divided
into a feed section, a high pressure section and a low pressure
section. The reactor was also equipped with the pressure drop
sensing monitor described in Example IV above. The reactor feed
section is equipped with lines for hydrogen, nitrogen and vacuum.
The high pressure section of the reactor has a forward pressure
regulator, a varying volume ballast reservoir and a pressure
transducer. The low pressure section is in-line with the reactor
and its pressure was monitored by a pressure transducer.
[0077] During each reaction, the gas consumption in the reactor
section caused a continuous pressure drop in the calibrated ballast
reservoirs. The pressure of the ballast, the autoclave pressure,
the tachometer reading, the hydrogen consumption and the reaction
temperature were continuously monitored and recorded as described
in Example IV.
[0078] In each reaction, 65 parts of wet catalyst (2G) was
transferred into the reactor beaker, washed with 12000 parts 95%
ethanol/5% water (Pharmco Products) and then the reactor was
sealed, and connected to EZE reactor. The system was evacuated and
filled with hydrogen followed by the addition of 28000 parts of an
ethanol solution which contains 3500 parts of 4-nitrotoluene via a
gas-tight syringe. The reactor was pressurized with hydrogen to the
indicated pressure (either 200 or 400 psig) and then heated to the
indicated temperature (either 125.degree. C. or 140.degree. C.).
When the temperature/pressure parameters were reached, stirring
(1300 rpm) and data acquisition was simultaneously initiated. After
gas absorption ceased the reactor was cooled and the liquid phase
extracted under pressure. Each set of reaction conditions was used
in duplicate runs. Table III below provides the initial catalyst
activity in terms of conversion of 4-nitrotoluene (mmol
H.sub.2/min) for each of the four conditions of the
temperature/pressure matrix.
3TABLE III Initial Catalyst Activity (Sample 2G) (mmol H.sub.2/min)
Reaction Temperature H.sub.2 Pressure psig 125.degree. C.
140.degree. C. 200 4.5 3.4 400 4.9 9.6
[0079] The above results show that increases in either temperature
or pressure alone do not enhance the catalytic activity of the
present catalyst (similar results are achieved with acid salt doped
catalyst). However, the subject catalyst shows synergistic high
catalyst activity under increased combined temperature/pressure
conditions.
EXAMPLE VI
[0080] A series of catalyst were tested for their response to
recycling reactions (each used in five consecutive (5) batch
reactions). The series included catalyst 2G and, for comparative
purposes. Catalysts formed according to Examples I (Sample I) and
Comparative Example II (Sample 5F) (see below). The reactions were
each carried out using the procedure and reactor equipment
described in Example VIII under temperature/pressure combined
conditions of 140.degree. C. and 400 psig. At the end of the fifth
cycle, the substrate (4-nitrotoluene) to catalyst contact ratio
reached a total of 250.
[0081] The results are shown in Table IV below. The precious
transition metal doped catalyst of the present invention exhibited
superior activity over the cycles tested when compared to undoped
catalyst (Sample 1) and to conventional acid salt doped catalyst
(Sample SF).
4TABLE IV Catalyst Activity in Batch Recycle Activity mmol
H.sub.2/min Cycle Sample 2G Sample 5F Sample 1 1 9.6 7.4 5.5 2 8.9
5.0 3.9 3 5.0 2.9 2.6 4 3.7 3.1 2.3 5 3.2 3.2 2.2
[0082] The above shows that undoped base metal catalyst had lower
catalytic activity in each of the five cycles than doped catalyst.
However, of the doped catalysts, the present doped catalyst
exhibited higher initial and overall activity than conventional
acid salt doped catalyst.
[0083] Comparative Example I
[0084] For comparative purposes, a sample of base metal catalyst
was prepared in the same manner as in Example II above except that
the dopant salt solution was formed with a solution of palladium
salt (NH.sub.3).sub.4Pd(OH).sub.2--H.sub.2O, having a pH of 13.7.
The resultant doped catalyst is labeled 1-Comparative. This high pH
dopant solution was used to prepare a doped catalyst formed with
the same nickel base catalyst of samples 2D (having a pre-dopant pH
of 11) and the same concentration (0.25 wt. percent) of Pd metal
dopant of those samples. The results are shown in Table I-C below
and compared with those of samples 2D.
5TABLE I-C Catalyst Slurry pH PM/Ni (atomic) Dopant Pre- Post-
Sample Sol. pH Doping Doping ICP XPS S/B 2D 9.1 11 9.7 0.00147 0.06
41 1-Comparative 13.7 11 11.9 0.0013 0.15 116
Comparative Example II
[0085] For comparative purposes, a series of palladium metal doped
nickel base metal catalysts were formed using the same procedure
described in Example II above except that acidic precious metal
salt solutions were used to provide the dopant metal. The samples
were analyzed in the same manner as described in Example II using
ICP and XPS techniques. The results are given in Table II-C. The
resultant doped catalyst products had very high S/B ratio showing
that a much greater fraction of the doped metal resided in the
surface volume of the catalyst particles.
6TABLE II-C Dopant (PM) Salt Bulk Analysis ICP Surface Vol Target
Catalyst Slurry pH Atom PM/Ni (atomic) Sample Conc. Salt pH
Pre-doping Post-doping % PM % Ni % Al PM/Ni (XPS) S/B Ratio 5A 1%
PdCl.sub.2 -0.2 9 6.7 0.92 93.8 5.0 0.00541 0.63 116 5B 0.5%
PdCl.sub.2 -0.2 11 7.6 0.51 92.3 6.9 0.00305 0.27 89 5C 0.25%
Na.sub.2Pd(II)Cl.sub.4 4.0 11 10.2 0.29 93.8 5.6 0.00171 0.17 100
5D 0.25% Na.sub.2Pd(IV)Cl.sub.6 2.0 11 10.2 0.28 93.5 5.9 0.00165
0.25 151 5E 0.25% Pd(NO.sub.3).sub.2 -0.7 11 11.1 0.28 93.7 5.7
0.00165 0.17 103 5F 0.25% PdCl.sub.2 -0.2 8.7 8.0 0.25 92.9 6.6
0.00149 0.18 121 5G 0.25% PdCl.sub.2 -0.2 9.0 8.1 0.26 93.9 5.5
0.00153 0.25 164 5H 0.25% PdCl.sub.2 -0.2 10 7.3 0.25 93.9 5.6
0.00147 0.17 116 5I 0.25% PdCl.sub.2 -0.2 11 9.2 0.27 93.3 6.1
0.00160 0.13 81 5J 0.25% PdCl.sub.2 -0.2 12 12.6 0.25 94.4 5.1
0.00146 0.13 89 5K 0.125% PdCl.sub.2 -0.2 11 8.0 0.124 95.0 4.6
0.00072 0.008 111
[0086] The data in Tables I-C and II-C shows a strong dependency of
the S/B ratio on the type of salt used and the, thus pH of the
dopant solution which provides the dopant precious metal. The high
S/B ratio attained when an acidic dopant salt or a very alkaline
dopant salt (Sample 1-Comparative) is used indicated that one does
not achieve the same type of dopant distribution as when using
dopant salts having a pH in the range of from about 8-12.
Comparative Example III
[0087] For comparative purposes, a series of Pd acid salt formed
catalysts, Samples 5G to 5J were tested in the same manner as above
and compared to Samples 2H, 21, 2F, and 2K in Table III-C below.
Each compared pair of samples contained 0.25 wt.% Pd dopant and
were formed using spongy nickel metal catalyst slurries having the
same pre-doping pH condition.
7 TABLE III-C Ni catalyst pre-doped pH Salt 9 10 11 12 NH3PdC12.H2O
77 77 85 62 PdCl.sub.2 61 74 68 61
[0088] The present basic salt formed doped catalyst provided a
higher activity in each comparison.
Comparative Example IV
[0089] For comparative purposes, duplicate hydrogenation reactions
of 4-nitrotoluene were conducted in the same manner as described in
Example V at reaction conditions of 140.degree. C. and 400 psig
except that the palladium doped nickel based catalyst used was
Sample 2G prior to washing and aging. The catalytic activity was
only 7.4 mmol H.sub.2/min compared to the 9.6 mmol H.sub.2/min
value obtained under the same conditions with the catalyst of the
present invention.
* * * * *