Modification Of ZnGa₂O₄ And CoFe₂O₄ Spinel And Its Catalytic Performance Of Methane Combustion

With the rapid growth of the global economy and population,the demand for energy is increasing rapidly.With the exhaustion of oil、coal and other primary energy sources,the consumption of natural gas is increasing.Methaneis the main component of natural gas.Its hydrocarbon ratio is lower than that of oil and coal,and the amount of carbon dioxide released by methane per unit of energy is lower than that of other hydrocarbon fuels.It comes form a wide range of sources and has huge reserves,making it a clean energy that can replace fossil fuels.But the methane combustion process produces nitrogen oxides and environmental pollutants like carbon monoxide and hydrocarbons.Therefore,it is of great significance to carry out research on methane catalytic combustion and reduce the environmental pollution caused by methane combustion.In this paper,the catalytic combustion of methane by Zn Ga₂O₄ and Co Fe₂O₄ spinel oxides with well thermal stability and low preparation cost has been studied.SEM,BET,XRD,O₂-TPD and XPS physical and chemical characterization and catalytic performance evaluation,the relationship between catalytic activity,structure and surface properties of these catalysts has been elucidated.In the second chapter,Zn_1-xCo_xGa₂O₄（x=0,0.1,0.3）series composite oxides were prepared by hydrothermal method,and their catalytic performance of methane was investigated.The radius of cobalt ion is similar to that of zinc ion,and the part of Zn²⁺in the tetrahedral（Td）position of Zn Ga₂O₄ is replaced by CO³⁺,the XRD results showed that the Zn_1-xCo_xGa₂O₄（x=0,0.1,0.3）microsphere catalysts were all spinel structures,which proved that the crystal structure of Zn Ga₂O₄ did not change after doping.X-ray photoelectron spectroscopy（XPS）analysis showed that the presence of Co³⁺in the Zn_1-xCo_xGa₂O₄（0.1,0.3）samples increased the lattice positive charge,resulting in the generation of interstitial oxygen to maintain its electrical neutrality.Oxygen temperature programmed desorption（O₂-TPD）spectra showed that Zn Ga₂O₄samples had only one species of oxygen desorption,while Zn_1-xCo_xGa₂O₄（0.1,0.3）samples had two species of oxygen desorption peaks.The first desorption at low temperature was surface adsorption oxygen,and the other was lattice oxygen.The catalytic methane combustion performance of the samples showed that the conversion rate at the same temperature was in the following order:Zn_0.7Co_0.3Ga₂O₄>Zn_0.9Co_0.1Ga₂O₄>Zn Ga₂O₄.Partially replacing Zn²⁺with Co³⁺can effectively increase the activity of Zn Ga₂O₄,in a certain range,the greater the amount of doping substitution,the better catalytic activity,when a certain reaction temperature is reached,these interstitial oxygen ions are released and participate in the catalytic combustion of methane,which improves the catalytic activity of the catalyst.In the third chapter,Co Fe₂O₄ spinel oxide was prepared by template method,and Ce O₂/Co Fe₂O₄ composite catalyst was prepared by supporting Ce O₂ on its surface.XRD results shows that we are successfully supported Ce O₂ on Co Fe₂O₄ support,SEM results show that the catalyst has micron scale and good dispersion.The results shows that the initiation temperature of Ce O₂/Co Fe₂O₄ catalyst is about 50℃lower than that of Co Fe₂O₄ support.The initiation temperature of Co Fe₂O₄ catalyst for methane combustion is 300℃and T₉₀ is 475℃,while the initiation temperature of Ce O₂/Co Fe₂O₄ catalyst for methane combustion is 250℃.T₉₀ is 430℃,the catalytic activity of Co Fe₂O₄ supported by Ce O₂ was increased.because Ce O₂ has a better capacity to store and release oxygen,it will have a better synergistic effect with the catalyst and has a higher catalytic activity for the catalytic combustion of methane.