掺杂SrTiO_3体系上甲烷氧化偶联催化性能的研究

A Study of Catalytic Properties of Doped SrTiO_3 Catalysts for Oxidative Coupling of Methane

用X—射线粉末衍射 (XRD)、氧吸附—程序升温脱附 (O2 -TPD)研究了柠檬酸热分解法制备的钙钛矿型催化剂的组成、结构与甲烷氧化偶联反应 (OCM)催化性能 ,结果表明钙钛矿型SrTi0 .9M0 .1O3 -δ(M =Mg ,Al,Zr)的B位掺杂离子的价态越低 ,脱附温度越高 ,这与催化剂对生成C2 产物的选择性相关联 ;钙钛矿型SrTi1-xMgxO3 -δ的B位Mg2 + 掺杂量越多 ,催化剂中的氧空位越多 ,脱附温度升高。当B位Mg2 + 掺杂量x≤ 0 1时 ,催化剂的甲烷转化率和C2 选择性明显增加 ,当x≥ 0 1时又明显下降。认为低价离子掺杂所产生氧空位为氧分子的活化提供了活性位 ,表面吸附态氧物种为OCM反应主要活性氧物种 ,较高温度脱附的吸附氧有利于甲烷氧化偶联C2 选择性的提高。

The structure and catalytic properties of perovskite-type catalysts for oxidative coupling of methane(OCM) have been studied by using X-ray diffraction (XRD)、Temperature-programmed desorption of oxygen(O 2-TPD) methods.It has been shown that doping the cations of lower valence (e.g.Mg 2+ ,Al 3+ ) to the B site of SrTi 0.9 M 0.1 O 3-δ perovskite-type catalysts results in the higher temperature desorption of adsorbed oxygen species on the surface of catalysts and thus higher C 2-selectivity for OCM reaction and doping Mg 2+ cations to the B site of SrTi 1-x Mg x O 3-δ Perovskite-type catalysts results in the formation of oxygen vacancies in the lattices of oxide catalysts and the higher temperature desorption of adsorbed oxygen species.With increasing the amount of Mg 2+ doped in the B site of SrTi 1-x Mg x O 3-δ ,methane conversion and C 2 selectivity first increase and then decrease remarkbly.The SrTi 1-x Mg x O 3-δ catalyst with x=0.1 has the highest methane conversion and C 2 yield.It is suggested that the oxygen vacancies of perovskite-type catalysts are the sites reponsible for oxygen activation,and the adsorbed oxygen species on the surface of catalysts are the main active species for OCM reaction.The adsorbed oxygen species that desorped at higher temperature are in favor of increase of C2 selectivity for OCM.