Selective hydrogenation of acetylene on Pd/SiO2 catalysts promoted with Ti, Nb and Ce oxides

Transition-metal oxides added to Pd/SiO2 improve significantly the activity and the ethylene selectivity of the catalyst in acetylene hydrogenation, w hich is caused by the interaction between the oxides and the Pd surface sim ilar to the case of the oxide-supported catalysts. It has been confirmed th rough experiments that metal oxides spread on and modify both geometrically and electronically the Pd surface after the catalyst is reduced at 500 deg reesC. Such a behavior of metal oxides in the catalyst is correlated well w ith their promotional effect on the catalyst performance. That is, the oxid es on the Pd surface retard the sintering of the dispersed Pd particles, su ppress the adsorption of ethylene in the multiply-bound mode, and facilitat e the desorption of ethylene produced by acetylene hydrogenation. Among the three metal oxides examined in this study, Ti oxide is found to have the m ost promotional effect. (C) 2000 Elsevier Science B.V. All rights reserved.