Abstract
In this study, 3%Pd/Al2O3, 3%Pt/Al2O3 and bimetallic (1%Pd + 2%Pt)/Al2O3 catalysts were examined in the total oxidation of methane in a temperature range of 150–400 °C. The evolution of the active component under the reaction conditions was studied by transmission electron microscopy and in situ extended X-ray absorption fine structure (EXAFS) spectroscopy. It was found that the platinum and bimetallic palladium-platinum catalysts are more stable against sintering than the palladium catalysts. For all the catalysts, the active component forms a “core-shell” structure in which the metallic core is covered by an oxide shell. The “core-shell” structure for the platinum and bimetallic palladium-platinum catalysts is stable in the temperature range of 150–400 °C. However, in the case of the palladium catalysts the metallic core undergoes the reversible oxidation at temperatures above 300 °C and reduced to the metallic state with the decrease in the reaction temperature. The scheme of the active component evolution during the oxidation of methane is proposed and discussed.
Highlights
Over the last decade, in the field of heterogeneous catalysis, specific attention has been paid to the synthesis of the bi- and trimetallic catalysts exhibiting unique properties in various catalytic reactions [1,2,3,4,5,6,7]
The differences in the catalytic activity of monometallic catalysts could be obviously explained by the higher activity of palladium than platinum in the total oxidation of methane [14,16,24,29]
The correct explanation of the catalytic activity should be based on the overall information about the atomic structure of the active component
Summary
In the field of heterogeneous catalysis, specific attention has been paid to the synthesis of the bi- and trimetallic catalysts exhibiting unique properties in various catalytic reactions [1,2,3,4,5,6,7]. The starting point in the development of bi- and trimetallic systems can be considered the application of the three-way catalysts (TWC) for the neutralization of the vehicle exhaust. Platinum provides a high rate of CO oxidation, palladium is known to be one of the most active catalysts for the total oxidation of hydrocarbons, and rhodium exhibits unique catalytic properties in the reduction of nitrogen oxides. Natural gas vehicles have become popular and the problem of the neutralization of unburned methane has arisen [13,14,15]
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