Bismuth as an additive modifying the selectivity of palladium catalysts

The influence of bismuth addition on the activity and selectivity of palladium catalysts supported on SiO2 in the reaction of glucose oxidation to gluconic acid was studied. The catalysts modified with Bi show much better selectivity and activity than palladium catalysts. The XRD studies proved the presence of intermetallic compounds BiPd and Bi2Pd, which probably increase activity and selectivity of PdBi/SiO2 catalysts in the oxidation of glucose. The TPO studies of catalysts containing 5 wt.% Pd/SiO2, 3 wt.% Bi/SiO2 and 5 wt.% Pd-5 wt.% Bi/SiO2 show that palladium oxidation occurs at much higher temperatures than in the case of bismuth. The maximum rate of I'd oxidation occurs at around 580 K while the maximum rate of Bi oxidation takes place at around 430 K. Considering the above facts, a reaction involving bimetallic catalysts in oxidizing atmosphere at 333 K should not lead to surface oxidation of palladium and thus their deactivation. (C) 2002 Elsevier Science B.V. All rights reserved.