Abstract
Methane, discovered in 1766 by Alessandro Volta, is an attractive energy source because of its high heat of combustion per mole of carbon dioxide. However, methane is the most abundant hydrocarbon in the atmosphere and is an important greenhouse gas, with a 21-fold greater relative radiative effectiveness than CO2 on a per-molecule basis. To avoid or limit the formation of pollutants that are dangerous for both human health and the atmospheric environment, the catalytic combustion of methane appears to be one of the most promising alternatives to thermal combustion. Total oxidation of methane, which is environmentally friendly at much lower temperatures, is believed to be an efficient and economically feasible way to eliminate pollutants. This work presents a literature review, a statu quo, on catalytic methane oxidation on transition metal oxide-modified ceria catalysts (MOx/CeO2). Methane was used for this study since it is of great interest as a model compound for understanding the mechanisms of oxidation and catalytic combustion on metal oxides. The objective was to evaluate the conceptual ideas of oxygen vacancy formation through doping to increase the catalytic activity for methane oxidation over CeO2. Oxygen vacancies were created through the formation of solid solutions, and their catalytic activities were compared to the catalytic activity of an undoped CeO2 sample. The reaction conditions, the type of catalysts, the morphology and crystallographic facets exposing the role of oxygen vacancies, the deactivation mechanism, the stability of the catalysts, the reaction mechanism and kinetic characteristics are summarized.
Highlights
Volatile organic compounds (VOCs) are environmental pollutants regarded as precursors for the formation of tropospheric ozone, the depletion of stratospheric ozone and the formation of photochemical smog in urban environments.The emission of VOCs by human activities and various industrial processes is a serious 4.0/).source of air pollution and is a problem for human health and the environment in general [1,2,3,4,5,6,7,8,9,10]
These results suggest a synergetic interaction between CuO and ceria support, which leads to a strong metal oxide-support interaction as the reason for enhanced catalytic activity in methane combustion
All these results indicated the potential of Ni modifying Ce-Zr systems to enhance considerably the catalytic performance in methane combustion by providing more reactive sites required for CH4 activation, as long as the modification process does not diminish to a great extent the specific surface area of the final materials
Summary
Volatile organic compounds (VOCs) are environmental pollutants regarded as precursors for the formation of tropospheric ozone (a greenhouse gas), the depletion of stratospheric ozone and the formation of photochemical smog in urban environments. The modification of ceria with various cations is known to affect oxygen mobility, which plays an important role in the catalytic combustion of methane [93,94] and improves stability towards sintering and the oxidation activity of the resulting catalysts. This modification leads to changes in redox properties and the creation of oxygen vacancies, both of which improve the oxygen exchange capacity between the gas phase and the catalyst and its oxygen storage capacity. The best polishing performance of this nano-grade ceria was 2258 Å/min for oxide films and 220 Å/min for nitrides [124]
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