Microcalorimetric studies of adsorption on the surface of Pd-Cu/SiO2

Adsorption of H-2, CO, O-2 and C2H4 on m (Pd)/m(SiO2) = 2%, m (Pd,Cu)lm(SiO2) [n(Pd)/n(Cu) = 1/1] = 2%, m (Pd,Cu)/m (SiO2) [n(Pd)/n(Cu) = 1/4] = 2% and m(Cu)/m(SiO2) = 8%, catalysts was investigated by using the techniques of microcalorimetric adsorption at, room temperature. The effect of O-2 on adsorption of C2H4 on the surface of the catalysts was also studied. It is found that the number of sites for Hz adsorption on Pd-Cu/SiO2 is close to that on Pd/SiO2. Addition of Cu decreases the sites of stronger adsorption and increases the sites of weaker adsorption of Hz and CO on Pd. On the other hand, Pd can promote the dispersion of;Cu on SiO2 and accelerate the rate of Oz adsorption on Cu/SiO2. These results suggest that Pd and Cu atoms are well mixed and Pd atoms are well dispersed in the Pd-Cu/SiO2 catalysts. Ethylene adsorbed on Pd/SiO2 produces ethylidyne and sigma and di-pi species. The addition of Cu inhibits the formation of the dissociatively adsorbed species-ethylidyne but promotes the formation of undissociatively adsorbed species-pi and di-sigma species for ethylene adsorption on Pd-Cu/SiO2 catalysts. Ethylene may react with Oz adsorbed on Pd/SiO2 at room temperature. Cu decreases the activity of adsorbed O-2 on Pd-Cu/SiO2. Hence, ethylene may be activated effectively on Pd-Cu catalysts.