Desorption and catalytic properties of palladium, supported on Al2O3-La2O3, prepared by the sol-gel method

Abstract

Desorption and catalytic properties of 0.3 wt% Pd catalysts supported on alumina-lanthana, prepared by the sol-gel method, were studied, A large excess of consumed hydrogen was observed during TPR experiments on these catalysts due to the partial reduction of lanthana. The enhanced hydrogen adsorption (H/Pd varies from 8 to 15) detected by TPD for these catalysts is supposed to be a consequence of spillover. Spillover of hydrogen is favored by a high dispersion of palladium on the support surface and the presence of lanthana reduced species. Palladium on alumina-lanthana catalysts show a higher catalytic activity than palladium on alumina catalysts because reduced species of lanthana stabilize palladium particles. Similarity of ammonia selectivity at high temperatures allows one to suggest that reduced lanthana is involved in the reaction on pure alumina-lanthana support and palladium on alumina-lanthana catalysts at these temperatures. A synergetic effect between small palladium particles and reduced species of lanthana is suggested to be responsible for observed behavior of the lanthana-promoted palladium catalysts.