DESORPTION AND CATALYTIC PROPERTIES OF PALLADIUM, SUPPORTED ON AL2O3-LA2O3, PREPARED BY THE SOL-GEL METHOD

Desorption and catalytic properties of 0.3 wt% Pd catalysts supported on alumina-lanthana, prepared by the sol-gel method, were studied. A l arge excess of consumed hydrogen was observed during TPR experiments o n these catalysts due to the partial reduction of lanthana. The enhanc ed hydrogen adsorption (H/Pd varies from 8 to 15) detected by TPD for these catalysts is supposed to be a consequence of spillover. Spillove r of hydrogen is favored by a high dispersion of palladium on the supp ort surface and the presence of lanthana reduced species. Palladium on alumina-lanthana catalysts show a higher catalytic activity than pall adium on alumina catalysts because reduced species of lanthana stabili ze palladium particles. Similarity of ammonia selectivity at high temp eratures allows one to suggest that reduced lanthana is involved in th e reaction on pure alumina-lanthana support and palladium on alumina-l anthana catalysts at these temperatures. A synergetic effect between s mall palladium particles and reduced species of lanthana is suggested to be responsible for observed behavior of the lanthana-promoted palla dium catalysts.