Palladium and palladium-copper catalysts supported on silica and niobia were characterized by H2 chemisorption and H2-O2 titration. Systems over silica were also analyzed by transmission electron microscopy and EXAFS. The metallic dispersion decreased from 20% to 7% when the content of Pd was increased from 0.5wt.-% to 3wt.-% in monometallic catalysts. The addition of 3 wt.-% Cu to obtain Pd-Cu catalysts caused a remarkable capacity loss of hydrogen chemisorption. TPR analysis suggested an interaction between the two metals and EXAFS characterization of the catalyst supported on silica confirmed the formation of Pd-Cu alloy. Pd/Nb2O5 catalysts showed turnover numbers higher than those obtained with the Pd/SiO2 systems in the cyclohexane dehydrogenation. However, the bimetallic catalysts showed very low turnover numbers.

Pt-Rh/Al2O3 catalysts prepared by successive incipient impregnations and coimpregnation were characterized by H2 chemisorption, temperature programmed reduction and benzene hydrogenation reaction in the vapor phase. The results showed that Rh plays the role of Pt reducting agent, which is very different from the effects of metal-metal interaction which appear mainly in solids with the highest metal contents. The most important parameter that results in bimetallic particles in the catalyst prepared by successive impregnation is the sequence of metal addition.