Surface structure and reaction performances of highly dispersed and supported bimetallic catalysts

Surface structures of Pt-Sn and Pt-Fe bimetallic catalysts have been invest igated by means of Mossbauer spectroscopy, Pt-L-III -edge EXAFS and H-2-ads orption. The results showed that the second component, such as Sn or Fe, re mained in the oxidative state and dispersed on the gamma-Al2O3 surface afte r reduction, while Pt was completely reduced to the metallic state and disp ersed on either the metal oxide surface or the gamma-Al2O3 surface. By corr elating the distribution of Pt species on different surfaces with the react ion and adsorption performances, it is proposed that two kinds of active Pt species existed on the surfaces of both catalysts, named M-1 sites and M-2 sites. M-1 sites are the sites in which Pr directly anchored on the gamma- Al2O3 surface, while M-2 sites are those in which Pt anchored on the metal oxide surface. M-1 sites are favorable for low temperature H-2 adsorption, and responsible for the hydrogenolysis reaction and carbon deposition, whil e M-2 sites which adsorb more H-2 at higher temperature, are more resistant to the deactivation due to less carbon deposition, and provide major contr ibution to the dehydrogenation reaction.