The Preparation And Characterization Of Co₃O₄-based Catalysts And The Catalytic Performance For Methane Combustion

Methane,the main component of natural gas,is regarded as the second most destructive greenhouse gas in the world,contributing approximately 20 times to global warming than carbon dioxide.In recent years,natural gas vehicles have been continuously promoted and popularized,but the emission of incompletely burned methane will cause atmospheric pollution.Catalytic combustion is considered to be one of the most effective ways to remove methane because of its low operating temperature and high efficiency.Therefore,looking for a catalyst with excellent activity and high thermal stability is the key to complete combustion of methane.Among the transition metals,Co₃O₄-based catalysts with spinel structure have attracted extensive attention due to their low cost,abundant resources and high activity.In our work,several series of Co₃O₄ catalysts were prepared to examine the influence of precursor,calcination temperature and the content of Zn O on their catalytic performance.The catalysts were systematically characterized using XRD,BET,SEM,TEM,XPS,H₂-TPR,etc.The structure and physicochemical properties combining with their performance were systematically discussed.The main contents were as follows:?1?A series of Co₃O₄ catalysts were prepared with different cobalt precursors?cobalt nitrate,cobalt acetate,cobalt chloride,cobalt sulfate?by precipitation method.It was found that the Co₃O₄-Ac catalyst prepared with cobalt acetate showed the best catalytic combustion performance for methane despite its small specific surface area.The surface analysis results showed that the Co₃O₄-Ac catalysts had the higher concentration of Co²⁺and adsorbed oxygen species than others,so it could be inferred that Co²⁺and adsorbed oxygen species play key roles for the complete combustion of methane.In addition,the Co₃O₄-Ac catalysts also had excellent stability,water resistance and cycle performance.?2?In order to prepare the Co₃O₄ catalysts with higher specific surface area and higher catalytic performance for methane combustion,the calcination temperature was adjusted during the preparation process.As a result,it was found that the calcination temperature had a great influence on the microstructure and activity of the Co₃O₄catalysts.With the decrease of the calcination temperature,the particle of the catalysts gradually decreased and their catalytic activity gradually increased.When the calcination temperature was 300oC,the Co₃O₄-300 catalyst had the smallest particle size and the largest specific surface area.Additionally,XPS results showed that the species.In summary,it could be inferred that the concentration of Co²⁺and adsorbed oxygen species,catalyst particles and specific surface area all play synergistic roles in the catalytic combustion of methane.?3?Zn O?x?-Co₃O₄ catalysts were prepared by co-precipitation in order to further improve the catalytic combustion performance of methane.Various characterization techniques were used to investigate the relationship between the microstructure of the catalyst and its catalytic activity.XRD and XPS results showed that Zn²⁺entering the on the surface and thus improved the catalytic performance.However,when the content was 50%,the catalytic performance of Zn O?50?-Co₃O₄ catalysts decreased significantly,it was likely due to the surface active sites of Co₃O₄ covered with excessive Zn O and the particle extremely agglomerated.It was worth noting that these three catalysts prepared with Zn O content of 5%,10%and 20%had similar and excellent catalytic performance.Combining XPS and H₂-TPR results,it was found that the species,but it didn't showed a significant advantage maybe due to the effect of dispersion and specific surface area.Therefore,it could be concluded that the appropriate content of Zn O could effectively improve the catalytic activity of Co₃O₄,in which Co²⁺and active oxygen species play important roles in the catalytic combustion for methane.In addition,factors such as the specific surface area and the degree of dispersion of the catalysts couldn't be ignored either.