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

Surface structures of Pt-Sn and Pt-Fe bimetallic catalysts have been investigated by means of Mössbauer spectroscopy, Pt-L₁₁₁-edge EXAFS and H_z-adsorption. The results showed that the second component, such as Sn or Fe, remained in the oxidative state and dispersed on the γ-Al₂O₃ surface after reduction, while Pt was completely reduced to the metallic state and dispersed on either the metal oxide surface or the γ-A1₂0₃, surface. By correlating the distribution of Pt species on different surfaces with the reaction and adsorption performances, it is proposed that two kinds of active Pt species existed on the surfaces of both catalysts, namedM1 sites and M₂ sites. M1 sites are the sites in which Pt directly anchored on the γ-Al₂O₃ surface, while M2 sites are those in which Pt anchored on the metal oxide surface. M_I sites are favorable for low temperature H₂ adsorption, and responsible for the hydrogenolysis reaction and carbon deposition, while M₂ sites which adsorb more H₂ at higher temperature, are more resistant to the deactivation due to less carbon deposition, and provide major contribution to the dehydrogenation reaction.