稀土莫来石型复合氧化物REMn_(2)O_(5)的结构与甲烷催化氧化性能研究  

Structure and Catalytic Performance of Manganese-based Mullite-type Mixed Oxides REMn_(2)O_(5) for Methane Complete Oxidation

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作  者:丁建财 吴炫锟 冉锐 吴晓东 翁端 杨志刚 Ding Jiancai;Wu Xuankun;Ran Rui;Wu Xiaoding;Weng Duan;Yang Zhigang(State Key Labo-ratory of New Ceramic and Fine Processing,School of Materials Science and Engineering,Tsinghua University,Beijing 100084,China)

机构地区:[1]清华大学材料学院,新型陶瓷与精细工艺国家重点实验室,北京100084

出  处:《中国稀土学报》2024年第1期30-39,I0001,共11页Journal of the Chinese Society of Rare Earths

基  金:国家重点研发项目(2016YFC0205000)资助。

摘  要:采用溶胶凝胶法制备了4种稀土莫来石型复合氧化物REMn_(2)O_(5)(RE=Pr,Sm,Eu,Y)并负载贵金属Pd,对比了其结构特点和甲烷催化氧化性能。结果表明,Pd/SmMn_(2)O_(5)和Pd/YMn_(2)O_(5)具有优异的甲烷催化氧化性能,其T_(50)分别为328和308℃,优于目前有报道的贵金属类甲烷氧化催化剂。XRD分析和DFT计算结果表明,稀土元素的离子半径对莫来石结构有明显影响,只有半径合适的离子(Sm,r=0.1079 nm;Eu,r=0.1066 nm)才容易形成莫来石相。Pr^(3+)离子半径较大(r=0.1126 nm),PrMn_(2)O_(5)样品出现较多的钙钛矿型氧化物;Y^(3+)离子半径较小(r=0.1019nm),YMn_(2)O_(5)样品中除莫来石相外同时还存在钙钛矿型氧化物和锰氧化物。稀土莫来石型复合氧化物中含有丰富的晶格氧且氧迁移能力优异。贵金属和莫来石之间的相互作用促进了Pd的高分散,显著提高了材料的晶格氧活性与可还原性,进而实现对甲烷催化氧化的有效促进。Manganese-based mullite-type mixed oxides REMn_(2)O_5(RE=Pr,Sm,Eu,Y) catalysts were prepared by a sol-gel method,and their catalytic activities for methane oxidation before and after the loading of palladium were evaluated.The results show that Pd/SmMn_(2)O_(5) and Pd/YMn_(2)O_(5) perform the optimized activities with the T50of 308 and 369 ℃,respectively,which are better than most of the reported noble metal-based catalysts.XRD analysis and DFT calculations demonstrate that the ionic radii of rare earth elements have a significant effect on the crystal structure of mullite,and only those with appropriate ionic radii(Sm,r=0.1079 nm;Eu,r=0.1066nm) can form mullite phase readily.Due to the large ionic radius of Pr(r=0.1126 nm),perovskite oxides phase noticeably appears in the PrMn_(2)O_(5) sample.With small ionic radius of Y(r=0.1019 nm),perovskite and manganese oxide phases also form in addition to the mullite.There is aboundant lattice oxygen with high mobility in the prepared manganese-based mullites.Strong interactions between Pd species and the mulites result in high dispersion of Pd and the enhanced reducibility of lattice oxygen in mullite,which further promote the catalytic activity for methane oxidation.

关 键 词:莫来石  甲烷氧化 晶格氧 稀土 

分 类 号:X734.2[环境科学与工程—环境工程] O643.36[理学—物理化学]

 

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