Supported palladium-gold catalysts and preparation of vinyl acetate therewith
Disclosed is a catalyst. The catalyst comprises palladium, gold, and a support comprising titanium dioxide and tungsten trioxide. The support preferably comprises from 75 wt % to 99 wt % of titanium dioxide and from 1 wt % to 25 wt % of tungsten trioxide. A method for preparing the catalyst is also disclosed. The method comprises impregnating the support with a palladium compound and a gold compound, calcining the impregnated support, and then reducing the calcined support. Further disclosed is a method for preparing vinyl acetate with the catalyst. The catalyst exhibits improved catalytic activity and selectivity.
1 . A catalyst comprising palladium, gold, and a support comprising titanium dioxide and tungsten trioxide.
2 . The catalyst of claim 1 wherein the support comprises from 75 wt % to 99 wt % of titanium dioxide and from 1 wt % to 25 wt % of tungsten trioxide.
3 . The catalyst of claim 2 wherein the support comprises from 80 wt % to 99 wt % of titanium dioxide and from 1 wt % of 20 wt % of tungsten trioxide.
4 . The catalyst of claim 3 wherein the support comprises from 80 wt % to 95 wt % of titanium dioxide and from 5 wt % to 20 wt % of tungsten trioxide.
5 . The catalyst of claim 1 which comprises from 0.1 wt % to 3 wt % of palladium and from 0.1 wt % to 3 wt % of gold.
6 . A method for preparing a catalyst, said method comprising:
(a) impregnating a support comprising titanium dioxide and tungsten trioxide with a palladium compound, a gold compound, and an optional alkali metal or ammonium compound;
(b) calcining the impregnated support; and
(c) reducing the palladium and gold compounds to metals.
7 . The method of claim 6 wherein the palladium compound is selected from the group consisting of palladium chloride, sodium chloropalladite, palladium nitrate, palladium sulfate, and mixtures thereof, and the gold compound is selected from the group consisting of auric chloride, tetrachloroauric acid, sodium tetrachloroaurate, and mixtures thereof.
8 . The method of claim 6 wherein the support comprises from 85 wt % to 95 wt % of titanium dioxide and from 5 wt % to 15 wt % of tungsten trioxide.
9 . The method of claim 6 wherein the calcination is performed at a temperature within the range of 100° C. to 600° C.
10 . The method of claim 6 wherein the reduction is performed at a temperature within the range of 300° C. to 600° C. in the presence of hydrogen.
11 . A method for preparing vinyl acetate comprising oxidizing ethylene in the presence of acetic acid and a catalyst which comprises palladium, gold and a support comprising titanium dioxide and tungsten trioxide.
12 . The method of claim 11 wherein the support comprises from 75 wt % to 99 wt % of titanium dioxide and from 1 wt % to 25 wt % of tungsten trioxide.
13 . The method of claim 11 wherein the support comprises from 80 wt % to 99 wt % of titanium dioxide and from 1 wt % of 20 wt % of tungsten trioxide.
14 . The method of claim 11 wherein the support comprises from 80 wt % to 95 wt % of titanium dioxide and from 5 wt % to 20 wt % of tungsten trioxide.
15 . The method of claim 11 wherein the catalyst comprises from 0.1 wt % to 3 wt % of palladium and from 0.1 wt % to 3 wt % of gold.