Preparation Of Three-dimensional Ordered Macroporous Skeletal Oxygen Storage Materials And Their Chemical Chain Reforming And Catalytic CO Oxidation Properties

Rare earth mixed oxides own great potential in catalysis due to the high oxygen storage capacity （OSC） and redox property. Ceria based and lanthanum based mixed oxides are the main types ofoxygen storage materials among the rare earth mixed oxides. Oxygen vacancy, specific surface area, surface plane, redox property and structure features were considered to be the key factors to affect the catalytic performance of the rare erath based catalysts.Three-dimensionally ordered macroporous （3DOM） materials own high thermal and chemical stability due to its special macroprous structure, which favours the gas molecules diffusion, reducing the diffusion resistence. In this case, an investigation on the relationship between the structure and catalytic property of macroprous rare earth materials has considerable scientific and technological values.In this paper, series of 3DOM rare earth （ceria based and lanthanum based） mixed oxides were prepared by a colloidal crystal template method. The structural evolution and synergistic reaction on the surface of loaded CeO₂/LaFeO₃ mixed oxides between CeO₂ and LaFeO₃ were studied in detail. The reduction behavior, OSC, thermal stability and redox property of mixed oxides were also investigated. The 3DOM rare earth mixed oxides were used as catalysts for chemical looping reforming of methane （CLRM） and CO oxidation to investigate the structural evolution, reaction mechanism and synergistic reaction in the catalytic process.In this paper, series of 3DOM ceria based mixed oxides with different Ce/Zr ratios, pore sizes and calcination temperatures were prepared. The structure, oxygen vacancy, oxygen mobility, surface area, surface plane, crystal size, reducibility, OSC and redox ablity were investigated in detail. It was found that, the introduction of Zr irons into ceria lattice leaded to lattice distortion, which created high concentration of oxygen vacancies, enhancing the mobility of lattice oxygen. The calcination temperature and the pore sizes could influence the specific surface area, grain size and mechnical stability of the materials. Compared with the nonporous samples, macroporous ceria based mixed oxides present a higher reactivity and thermal stability.As the oxygen carrier,3DOM ceria based mixed oxides own high activity for CLRM. During the reaction between methane and the mixed oxides, surface CeO₂ was first reduced to create sites for activating both reactants （methane and oxygen in solid solution）. The methane on these sites was activated to carbonaceous species and hydrogen, allowing the carbon deposition to be selectively oxidized to CO by activated oxygea During the water spiltting reaction, the water molecule was reduced to hydrogen. The reduced oxygen carrier gained oxygen from water molecule to achieve regeneratioa It was found that ceria based oxygen carrier own better carbon resistance. Only pure hydrogen was detected in the water spiltting reaction, and the carbonaceous species such as CO and CO₂ could not be observed. Compared with the pure 3DOM CeO₂,3DOM CeO₂-ZrO₂ solid solutions own higher reactivity for CLRM and larger amounts of H₂.As the catalysts,3 DOM ceria based mixed oxides showed high activity for CO oxidation. The catalytic performance of ceria based catalysts was dominated by one{110} surface plane. There are two pathways for CO oxidation reaction mechanism:the first pathway is that the adsorption of O2 on the oxygen vacancy direct with CO adsorbed on the surface of CeO₂ to form gaseous CO₂; The second pathway is the decomposition of carbonate species to form gaseous CO₂. The first pathway is considered the major pathway for CO oxidation over 3 DOM CeO₂/CeO₂-ZrO₂ catalysts due to the larger amount of oxygen vacanies. On the other hand, the second pathway is the major pathway for CO oxidation over 3DOM CeO₂. It was found that catalyst deactivation was closely related to the buildup of carbonate species, which blocked active sites for CO oxidation.Series of loaded 3 DOM CeO₂/LaFeO₃ mixed oxides were prepared and the influence of CeO₂ loading on the materials was also studied. The introduction of CeO₂ into LaFeO₃ surface enhanced the concentrations of oxygen vacancies, oxygen mobility, OSC and redox property. The CeO₂ particles could be distributed well on the 3DOM LaFeO₃ surface by adjusting the CeO₂ loading. It was found that hydrogen spillover on the interface of materials, indicating that strong interaction existed on the interface between CeO₂ and LaFeO₃.The loaded 3DOM CeO₂/LaFeO₃ mixed oxides also showed higer reactivity for CLRM. The introduction of CeO₂ inhibited the formation of carbon deposition in the methane selective oxidation. Therefore, no carbonaceous gas was detected in the water splitting reaction with the production of pure hydrogea 3DOM CeO₂/LaFeO₃ mixed oxides still showed higher reactivity even after 30 redox cycles.Compared with pure CeO₂ and LaFeO₃, loaded 3DOM CeO₂/LaFeO₃ mixed oxides showed higher CO activity. The in situ DRIFT investigation showed that both chemical adsorption and physical adsorption exist on the surface of CeO₂/M-LaFeO₃ mixed oxides, indicating a stronger interaction. CO adsorbed on the surface of CeO₂/M-LaFeO₃ with the formation of carbonate, which decomposed to CO₂ easily. It was found that no carbonate accumulate on the surface of the materials, due to the rate of carbonate formed was similar with the carbonate decomposed, leading to a higher activity and no deactivation. In addition, the in situ DRIFT of CO adsorption present a peak at 2007cm-1, indicating a stronger physical adsorption.