A quantity of reagent grade tin metal or compound, chloride-free, and high-surface-area silica spheres are placed in deionized water, followed by deaerating the mixture by boiling and adding an oxidizing agent, such as nitric acid. The nitric acid oxidizes the tin to metastannic acid which coats the spheres because the acid is absorbed on the substrate. The metastannic acid becomes tin oxide upon drying and calcining. The tin-oxide coated silica spheres are then placed in water and boiled. A chloride-free precious metal compound in aqueous solution is then added to the mixture containing the spheres, and the precious metal compound is reduced to a precious metal by use of a suitable reducing agent such as formic acid. Very beneficial results were obtained using the precious metal compound tetraammine platinum(II) hydroxide

Davis, Patricia

Miller, Irvin M.

Upchurch, Billy T.

English

NASA Technical Reports Server

United States Patent [191 
Upchurch et al. 
[54] 
[75] Inventors: Billy T. Upchurch, Virginia Beach; 
Patricia A. Davis; Irvin M. Miller, 
both of Newport News, all of Va. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
PROCESS FOR MAKING A NOBLE METAL 
ON TIN OXIDE CATALYST 
[73] Assignee: The United States of America as 
[21] Appl. No.: 90,874 
[22] Filed: Aug. 31, 1987 
[51] Into (3.4 .............................................. BOlJ 23/62 
[52] U.S. C1. .................................... 502/339; 502/325; 
502/344 
[58] Field of Search ............... 502/242, 249, 325, 339, 
502/344 
1561 References Cited 
U.S. PATENT DOCUMENTS 
2,079,404 5/1937 Harris ............................. 502/261 X 
2,840,528 6/1958 Mills et 
............ 252/455 
........ 502/261 X 
3,535,270 10/1970 Mulaskey ...... ............ 502/239 
4,524,051 6/1985 Wright et al. ....................... 423/247 
[ i l l  Patent Number: 4,855,274 
1451 Date of Patent: Aug. 8, 1989 
4,590,177 5/1986 Richard et al. ................. 502/261 X 
FOREIGN PATENT DOCUMENTS 
0107471 10/1983 European Pat. Off. . 
107471 5/1984 European Pat. Off. . 
OTHER PUBLICATIONS 
Above References A, C and L were Cited by Appli- 
cants. 
Primary Examiner-W. J. Shine 
Attorney, Agent, or Firm-George F. Helfrich; Charles 
E. B. Glenn; John R. Manning 
t571 ABSTRACT 
A quantity of reagent grade tin metal or compound, 
chloride-free, and high-surface-area silica spheres are 
placed in deionized water, followed by deaerating the 
mixture by boiling and adding an oxidizing agent, such 
as nitric acid. The nitric acid oxidizes the tin to meta- 
stannic acid which coats the spheres because the acid is 
adsorbed on the substrate. The metastannic acid be- 
comes tin-oxide upon drying and calcining. The tin- 
oxide coated silica spheres are then placed in water and 
boiled. A chloride-free precious metal compound in 
aqueous solution is than added to the mixture containing 
the spheres, and the precious metal compound is re- 
duced to a precious metal by use of a suitable reducing 
agent such as formic acid. Very beneficial results have 
been obtained using the precious metal compound tet- 
raammine platinum(I1) hydroxide. 
7 Claims, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=19900010864 2020-03-24T03:15:06+00:00Z
4,855,274 
1 2 
deaerating the mixture by boiling, and adding an oxidiz- 
ing agent, such as nitric acid. The nitric acid oxidizes 
the tin to metastannic acid which coats the spheres 
because the metastannic acid will be adsorbed on the 
5 substrate. The metastannic acid will become tin-oxide 
Upon drying and Calcining. The tin-oxide coated Silica 
spheres are then placed in water and boiled. A chloride- 
free preCiOUS metal compound in aqueous Solution is 
then added to the mixture containing the spheres, and 
10 the precious metal compound is reduced to a precious 
metal by use of a suitable reducing agent such as formic 
acid. Very beneficial results have been obtained using 
the precious metal compound tetraammineplatinum (11) 
hydroxide. 
DETAILED DESCRIPTION OF THE 
INVENTION 
PROCESS FOR MAKING A NOBLE METAL ON 
TIN OXIDE CATALYST 
ORIGIN OF THE INVENTION 
The invention described herein was made jointly in 
‘)he performance of work under NASA Contract N ~ .  
NAS1-18252 and employees of the United States Gov- 
emment. In accordance with 35 UsC 202, the contrac- 
tor has elected not to retain title. 
BACKGROUND OF THE INVENTION 
This invention relates to a method of producing a 
noble metal catalyst, and more particularly, to a method 
of producing a metal on metal oxide catalyst for use in l5 
a carbon dioxide laser. 
In a closed cycle carbon dioxide laser, a high voltage 
discharge is used to initiate laser emission. However, The present invention comprehends producing a 
this electrical discharge also causes some of the carbon noble metal on metal oxide catalyst on an inert, high- 
dioxide in the laser to partially dissociate into carbon 2o surface-area support material which will function as a 
monoxide and oxygen in the high voltage discharge catalyst at approximately room temperature using chlo- 
region. The continual dissociation Of carbon monoxide ride-free reagents. This is accomplished in a two-step 
during laser operation causes the concentration of car- process. In the first step, a commercially available, in- 
bon dioxide to decrease and that of carbon monoxide ert, high surface area support material, such as high 
and oxygen to increase. The loss of carbon dioxide 25 surface area silica spheres, is coated with a thin layer of 
the coated support is then coated with a thin layer of a 
equivalent. The purpose of these thin layers is to main- 
the pores in the support. 
The first step is accomplished by first preparing a 
mixture of a commercially available, inert, high-surface- 
coupled with the gain in oxygen a rapid loss in metal oxide, a monolayer equivalent. In the second step, 
laser power. To maintain laser power, it is necessary to 
While different catalysts have been used to effect the 
C02 laser demands a catalyst which is very efficient at 
room temperature. It has been found that noble metal 
on tin(1V) oxide catalysts supported on an inert sub- 
strate are effective under such conditions. There are 
recombine the carbon monoxide and oxygen products. precious metal amounting to a fraction of a monolayer 
monoxide and Oxygen, the 30 tain the high surface area of the catalyst by not blockng recombination Of 
several known methods of making such catalysts. How- 35 area 
ever, all of these processes include either time consum- 
such as high-surface area 
spheres, and an Oxidizing agent* Very resu1ts 
ing extra drying and calcining steps or the use of &lo- have been obtained using nitric acid as an oxidizing 
ride-containing materials. The use of &loride contain- agent since it leaves no residue. It is also helpful if the 
ing compounds necessitates thorough washing of the spheres are first deaerated by boiling in water to allow 
catalyst, because &loride is known to poison and deac- 4o the entire surface to be coated. A metal, such as tin, is 
tivate the catalyst. Consequently, a need continues to then dissolved in the oxidizing agent/suPPort material 
exist for a chloride-free method of producing a mixture to yield, in the case of tin, metastannic acid. 
noble metal on metal oxide catalyst for use in a closed- Although tin has proven especially beneficial for use in 
cycle C02 laser. a closed-cycle C02 laser, in general any metal with two 
Accordingly, it is an object of this invention to pro- 45 Valence States, such as most transition metals and anti- 
vide a simple method of producing a noble metal on mony, may be used. The metastannic acid will be ad- 
metal oxide catalyst on an inert, high-surface area sub- sorbed onto the high-surface-area spheres and coat the 
strate using chloride-free reagents for use in a C02 laser. spheres. Any excess oxidizing agent is then evaporated 
A further object of this invention is to provide a and the resulting metastannic acid-coated spheres are 
one-step method of adding a layer of a metal oxide to an 50 dried and calcined, whereby the metastannic acid be- 
inert support material. comes tin(1V) oxide. 
A further object of this invention is to provide a The second step is accomplished by preparing an 
one-step method of adding a layer of a noble metal to aqueous mixture of the tin(1V) oxide coated spheres and 
metal oxide on an inert support. a soluble, chloride-free salt of at least one catalyst metal. 
A further object of this invention is to provide a 55 The catalyst metal may be selected from the group 
method of producing a noble metal on metal oxide cata- consisting of platinum, palladium, ruthenium, gold and 
lyst wherein the reagents used and products formed rhodium or other platinum group metals. Extremely 
during the reaction are either volatile or decompose to beneficial results have been obtained using chloride-free 
volatile products during drying. salts of platinum, palladium, or a combination thereof, 
Other objects and advantages of this invention will 60 such as tetraammine platinum(I1) hydroxide 
become apparent hereinafter in the specification which (Pt(NHj)4(0H)2) or tetraammine palladium nitrate 
follows. (Pd(NH3)4(N03)2). It is also beneficial if the coated 
spheres are first deaerated by boiling. The platinum salt 
will be adsorbed onto the high surface area and coat the 
According to the present invention, the foregoing 65 spheres. A chloride-free reducing agent is then added to 
the aqueous mixture whereby the catalyst metal is de- 
posited on the tin(1V) oxide coated spheres. Any reduc- 
ing agent which decomposes to volatile products and 
SUMMARY OF THE INVENTION 
and additional objects are attained by placing a quantity 
of reagent grade tin metal or compound, chloride-free, 
and high-surface-area silica spheres in deionized water, 
4,855,274 
3 4 
water upon reaction or drying may be used. Formic for that many moles. This same procedure can be used 
acid, hydroxylamine (NHzOH), hydrazine (N2H4), and for any other metal oxide and a known B E T .  area of 
ascorbic acid are particularly advantageous. After the the support. The example also indicated 3.5 grams of 
metal has been deposited on the tin(1V) oxide coated Pt(NH3)4(QH)2 for + monolayer equivalent of Pt on the 
spheres the solution is evaporated to dryness, whereby 5 surface. This was calculated by taking $ the number of 
the desired noble metal on metal oxide catalyst is ob- moles of SnO2 for the moles of Pt required, then con- 
tained. verting that to the weight of Pt(NH3)4(QH)2 to be 
The present invention is particularly advantageous added in the second step. 
because the method of foeming and applying tin oxide The above procedure can be used to calculate the 
to a substrate is a one-step process that results in a more 10 amount of any metal oxide for a monolayer equivalent 
uniform application than other methods. Similarly, the 
method of forming and applying a precious metal to What is claimed is: 
either tin oxide or an inert substrate is a one-step process 1. A method of coating a porous, high surface area, 
and occurs at a lower temperature than that commonly ceramic support material with a catalyst comprising 
used by other processes. Most importantly, the present 15 tin(1V) oxide overlaid with a noble metal, which pro- 
invention is inherently clean because excess reagents, cess comprises chemically forming in one step a thin 
such as nitric acid and formic acid, as well as unwanted tin(1v) oxide coating form solution directly on the ce- 
products, such as nitrates and formates, all decompose ramic support material followed by chemically forming 
and are removed from the system by simple evaporation in on step a thin noble metal coating from solution di- 
without the necessity to separate them by filtration or 20 rectly on the tin(1V) oxide-coated ceramic support ma- 
washing. Furthermore, as it is possible to apply ex- terial, the tin(1V) oxide coating and the thin noble metal 
tremely thin layers of the tin oxide and precious metals, coating each having an amount of matter therein equiv- 
the present invention is able to coat high-surface area alent to about that contained in a monolayer, the ce- 
substrates without appreciably blocking small pores, ramic support material being first immersed in deion- 
which greatly increases the efficiency of the catalyst. 25 ized water, after which metastannic acid is provided 
For example, prior methods have yielded a catalyst therein, the metastannic acid having been generated by 
with a B.E.T. surface area between approximately 65 a process which leaves no residue to act as a poison for 
m2/g and 70 m2/g. By contrast, the present invention the catalyst, whence the metastannic acid is absorbed on 
has yielded the same catalyst with an increased B.E.T. the ceramic support material, whereupon the metastan- 
surface of approximately 170 m2/g. 30 nic acid becomes tin(1V) oxide upon evaporation and 
It should become obvious to those skilled in the art drying. 
that this invention is not limited to the examples herein 2. The method of claim I, wherein the metastannic 
described. acid is generated by dissolving tin metal in an acid, any 
excess of which acid and any unwanted products of the 
35 reaction thereof with tin metal being vaporizable or EXAMPLE 
Ten grams of commercially available, high surface decomposable to volatile products upon heating, 
area silica spheres, 10 microns in diameter, having a thereby leaving an uncontaminated thin layer of tin(1V) 
B.E.T. surface area of 167 m2/g, were placed in deion- oxide on the ceramic support material. 
ized water. Two grams of reagent grade tin powder 3. The method of claim 2, wherein the acid is nitric 
were added. This was an amount sufficient to coat the 40 acid. 
spheres with one monolayer equivalent of tin(1V) oxide. 4. The method of claim 3, wherein the metastannic 
The water was boiled for 4 minutes to deaerate the acid absorbed on the support is converted to tin(1V) 
solids. After cooling the liquid, nitric acid was added to oxide by evaporation and drying to remove excess 
obtain a 2.25 molar concentration. The mixture was water and nitric acid. 
then slowly stirred and heated to 50" C. A white suspen- 45 5. The method of claim 3, wherein the amount of tin 
sion settled out and the temperature was raised to 110" metal employed is calculated to result in a thin coating 
C. for overnight evaporation and drying. Twenty two of tin(1V) oxide on the support material in an amount 
grams of deionized water were added to the dried pow- equivalent to that contained in a monolayer without 
der, and boiled again for 3 minutes to deaerate it. Then, appreciable blocking of the pores of the support mate- 
3.5 grams of Pt(NH3)4(QH)2 (sufficient for + monolayer 50 rial, whereby an efficient catalyst is produced. 
equivalent of Pt on the surface of the spheres) was dis- 6. The method of claim 1, wherein the noble metal is 
solved in 78 grams of hot deionized water. This solution selected from the group consisting of platinum and 
was added to the hot water containing the spheres and palladium, and the noble metal coating is chemically 
stirred slowly. To reduce the Pt(NH3)4(OH)2 to plati- formed from solution directly on the tin(Iv) oxide- 
num metal, 6 equivalents of formic acid (3 g of 88%) 55 coated ceramic support material by a process which 
were added and the solution was heated to just over leaves no residue to act as a poison for the catalyst. 
loo" C. overnight to evaporate to dryness. The catalyst 7. The method of claim 6, wherein the tin(1V) oxide- 
product was a dark powder consisting of a monolayer coated support material is immersed in deionized water 
equivalent of tin(1V) oxide on 10 micron diameter silica after which a platinum or palladium compound is added 
spheres, with a + monolayer loading equivalent of plati- 60 and is absorbed from solution onto the surface of the tin 
num metal. oxide, followed by reduction of the noble metal com- 
The preceding example called for 2 grams of tin for a pound to noble metal by a soluble reducing agent, the 
monolayer equivalent of tin oxide on 10 grams of high reducing agent and all products of the reduction reac- 
surface area silica spheres having a B.E.T. area of 167 tion except the metal, decomposing or vaporizing upon 
m2/g. The amount of tin was calculated by knowing the 65 heating, whereby an uncontaminated metal coating is 
area of a 0-Sn-0 surface molecule and extrapolating formed on the tin(1V) oxide-coated ceramic support 
that area to 167 m2/g for 10 grams to obtain the number material. 
and a fractional monolayer of precious metal. 
of moles of SnO2, and hence the amount of tin required * * * * *  


Process for making a noble metal on tin oxide catalyst

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