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. 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 monometallic Au/Al2O3, MxOy/Al2O3 (M=Cu; Ce) catalysts and bimetallic catalysts with simultaneously (Au+MxOy) and sequentially (MxOy/Au, Au/MxOy) deposited metals were prepared. Oxidation of CO in the presence of these catalysts at 50-450 °C was studied. The activity of the catalysts increases in the following series: MxOy/Au/Al2O3> Au/MxOy/Al2O3> (Au+MxOy)/Al2O3 > CuxOy/Al2O3 > Au/Al2O3 >CexOy/Al2O3. A synergistic effect was detected at 50-250 °C: bimetallic catalysts converted up to 50 % of CO to CO2, while the monometallic samples were inactive. Increasing the reaction temperature above 250 °C results in a decreased synergistic effect, although bimetallic catalysts still possess good activity. The electronic and structural organization of the catalyst active sites before and after the reaction were studied by means of XRD, TEM, EDX, XPS, and DRIFTS techniques. The causes for the synergistic effect and the reaction mechanism in the presence of synergistic catalysts are proposed and discussed.