ИСТИНА

The synergism of catalytic activity is a sharp increase in the reaction rate in the presence of a bimetallic catalyst (M1 –M2/support) as compared with the sum of the reaction rates in the presence of monometallic analogues (M1/support and M2/support). Study of the synergistic effect in CO oxidation is of obvious interest for developing new approaches to the synthesis of high-performance and stable catalysts able to oxidize CO at room temperature. Currently, it is possible to distinguish metal compositions possessing high synergistic activity in the lowtemperature CO oxidation. These include Au–Cu, Au–Ce, Pt–Cu, Pt–Rh, and Pd– Cu deposited on various supports. Despite the substantial array of experimental data, the development of optimal synergistic catalysts is still hampered by poor knowledge of the nature of active sites and the reaction mechanism. In the present study some bimetallic Cu/Pd/Al2O3, Pd/Cu/Al2O3, Pd+Cu/Al2O3 catalysts and their monometallic analogues (Pd/Al2O3, Cu/Al2O3) were prepared by deposition-precipitation and impregnation. CO oxidation on these catalysts at 273–723 K was studied. A strong synergistic effect in CO oxidation was detected: the reaction on bimetallic catalysts starts at a 150–200 K lower temperature than on monometallic samples; and the apparent activation energy for CO oxidation on Cu/Pd, Pd/Cu, Pd+Cu, Pd and Cu catalyst was 20, 30, 37, 60 and 76 kJ/mol, respectively. The catalysts were studied by means of TEM, EDX, XPS and EPR techniques. The relationship between the magnitude of synergistic effect and concentration of specific structure sites (coordinative unsaturated atoms) and electronic sites (metastable Cu2O and PdO2 oxides) in the bimetallic catalysts was elucidated. A mechanism for synergistic CO oxidation was proposed and discussed.