METAL OXIDE CATALYSTS ON STRUCTURED CERAMIC SUPPORTS FOR METHANE LOW TEMPERATURE BURNING
Nanosized Pd-Co3O4-ZrO2-catalysts have been developed on monolithic matrices (Al2O3/cordierite) of honeycomb structure that exhibit stable activity in low-temperature catalytic non-flammable methane combustion and are promising for use in portable catalytic heat generators. For the purpose of the structural and functional design of an efficient catalyst for the target process, studied is the effect of composition and method of preparation of catalysts containing 3d-metal (Co) oxide and ZrO2 in the porous matrix of Al2O3 as the secondary support, formed on the surface of the cordierite monoliths, on the functional properties of the catalytic compositions in the process of deep oxidation of methane in a stoichiometric mixture with oxygen. Based on X-ray diffraction data, it was substantiated that aluminium oxide as a secondary carrier is a mixture of amorphous and γ-modification of Al2O3. In this case, the crystallization with the formation of the phase γ-Al2O3 occurs when the material is calcined at a temperature of 850 oC. According to the analysis of images of transmission electron microscopy (TEM), the size of the palladium nanoparticles formed in the catalytic coating, obtained by thermal decomposition of aluminium nitrate, is 8-15 nm. It has been shown that zirconia contributes to the stable activity of catalysts by preventing the high-temperature interaction of cobalt and aluminum oxides with the formation of low active Co-Al spinel. The introduction of palladium into the composition of Co3O4/Al2O3/cordierite reduces the strength of the bond of oxygen with the catalyst, which increases its activity; the role of palladium within the Pd-So3O4/Al2O3/cordierite is also in increasing the stability of the Pd-Co3O4 composition under reaction conditions. Simultaneous application of Co3O4 and Pd compared with successive one causes the formation of a more active catalyst. The developed catalytic compositions exhibit stable activity under reaction conditions for seven cycles of operation. Ref. 14, tab. 2, fig. 3.
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