Optimizing the Reaction Performance of La2Ce2O7‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations. Issue 2 (11th December 2018)

• Record Type: Journal Article
• Authors: Xu, Junwei; Zhang, Yan; Liu, Yameng; Fang, Xiuzhong; Xu, Xianglan; Liu, Wenming; Zheng, Renyang; Wang, Xiang
• Is Part Of: European journal of inorganic chemistry. Issue 2(2019)
• Page Start: 183
• Page End: 194
• Publication Date: 2018-12-11
• Subjects: Lanthanides -- Doping -- Electron‐deficient compounds -- Nonstoichiometric compounds -- Oxidative coupling -- Solid‐state structures; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201801250
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : To optimize the reaction performance of La2 Ce2 O7 for OCM, catalysts with varied La/Ce molar ratios and doped by Ca additive have been synthesized and characterized by different techniques. It is discovered that a La2 Ce2 O7 compound having a disordered cubic defective fluorite phase is predominantly formed in all the samples. Varying the La/Ce ratio influences the fine crystalline structure of the catalysts. As a result, the abundance of the surface facile oxygen and alkaline sites increase by increasing the La/Ce ratio. Moreover, the Ca additive exists on the surface of Ca0.5 La2 Ce2 O7 and Ca0.5 La1.5 Ce2 O7 as dispersed CaCO3, which covers the active sites and is harmful to the OCM reaction. However, for La2 Ce1.5 Ca0.5 O7, the major part of the Ca additive has entered into the lattice of La2 Ce2 O7 phase as Ca 2+ cations, thus creating more oxygen vacancies and improving the surface alkalinity of the catalyst, which is favorable to the OCM reaction. Both the active surface oxygen and alkaline sites are vital for OCM, and their synergism determines the reactivity. By increasing La/Ce ratio and doping Ca 2+ into La2 Ce2 O7 lattice, the quantities of both kinds of active sites can be significantly improved, thus obtaining catalysts with much improved reaction performance. La2 Ce1.5 Ca0.5 O7 owns the largest amount of both types of active sites, hence depicting the best reaction performance, over which the highest C2 yield of 22.5 % can be achieved even at 750 °C. Abstract : Lattice Ca 2+ Boost: Ca 2+ cations doped into the lattice matrix of La2 Ce2 O7 phase improve both the quantities of surface‐active oxygen and alkaline sites of the promoted catalyst, hence boosting its OCM reaction performance remarkably.