Preparation Of Ce_1-xFe_xO₂ Mixed Oxides And Their Performance For Methane Combustion

Ceria has been widely used as a promoter and an oxidation catalyst because ofits unique redox properties and high oxygen storage capability. The important role ofceria played in catalytic reactions is suggested to be the generation and participationof surface oxygen species and anionic vacancies in the catalytic reactions. A numberof more recent studies have shown that these redox properties can be significantlyenhanced if additional elements are introduced into ceria lattice by forming solidsolutions. Thus, varies binary ceria-based catalysts have been studied with thepurpose of increase the thermal stability and OSC of the CeO₂.In this paper, sol-gel method and coprecipitation method were used to prepareCe_1-xFe_xO₂ mixed oxides, and methane combustion were uesed as the probe reaction.The effects of amounts of doped Fe₂O₃, precipitation agents, preparation methodsand calcination temperature of catatlysts for methane combustion were studied. Andwe also studied the effect of different supports of NiO catalysts for methanecombustion. The prepared samples are characterized by XRD, DRS,nitrogenadsorption-desorption experiments and H₂-TPR.1. Ce_1-xFe_xO₂ mixed oxides of different amount (x=0.1-0.5) were prepared bycitric acid sol- gel method and microwave technique. The results showed thatCe_1-xFe_xO₂ mixed oxides have higher catalytic activity for methane combustion thanpure CeO₂, especially for Ce_0.9Fe_0.1O₂, its T₁₀ and T₉₀ are 415℃and 550℃,respectively, which are 60℃and 113℃lower than the corresponding temperaturesof T₁₀ and T₉₀ over CeO₂.The surface area of CeO₂ are increased by the dope ofFe₂O₃, and oxygen vacancies are formed as Fe³⁺ and Ce⁴⁺ have different radius,which are benefit to the activate of methane, then can improve the catalytic activityof methan combustion.2. A series of Ce_0.9Fe_0.1O₂ catalysts were prepared with different precipitationagents.The Catalytic activities for methane combustion over Ce_0.9Fe_0.1O₂ mixedoxides were investigated. The results showed that NH₃·H₂O+ (NH₄)₂CO₃ mixedsolution precipitation agents is better than that of others. The catalyst prepared by NH₃·H₂O+ (NH₄)₂CO₃ mixed solution precipitation agents has higher surface area,small crystallize, more redox Ce⁴⁺(?)Ce³⁺ and lower activation energy.3. Compared with sol-gel method, the catalyst prepared by coprecipitation hashigher activity for methane combustion.4. Ce_0.9Fe_0.1O₂ mixed oxide catalysts were prepared by coprecipitation methodand calcined at 500, 600 and 700℃, respectively. The influence of the calcinationtemperature of the mixed oxide catalysts on the performance for methane combustionwas studied. It is showed that all the catalysts prepared at this temperaturerange(500℃-700℃) are mesoporous materials. The catalysts calcined at 500℃hasthe higher surface area, smaller crystallize, strong redox ability, and it has the bestactivity for methan combustion. The catalytic activity order of the catalysts isCe_0.9Fe_0.1O₂(500)＞Ce_0.9Fe_0.1O₂(600)＞Ce_0.9Fe_0.1O)2(700).5. Ce_0.9Fe_0.1O₂ andγ-Al₂O₃ were used as the supports to prepare NiO catalysts.The infulence of the support for loaded NiO catalysts were studied. The results showthat NiO are highly disperse in the Ce_0.9Fe_0.1O₂ surface and there are some interationbetween them; while some NiAl₂O₄ were formed for theγ-Al₂O₃ supported NiOcatalysts. The formation of NiAl₂O₄ restrain the activity for methane combustion.Though NiO/Al₂O₃ has higher surface area, its catalytic activity is lower than that ofNiO/Ce_0.9Fe_0.1O₂.