Influence of Cesium Loading on Oxidative Coupling of Methane (OCM) over Cs/SnO 2 Catalysts
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ORIGINAL ARTICLE
Influence of Cesium Loading on Oxidative Coupling of Methane (OCM) over Cs/SnO2 Catalysts Junwei Xu1 · Yameng Liu1 · Xianglan Xu1 · Yan Zhang1 · Rong Xi1 · Zhixuan Zhang1 · Xiuzhong Fang1 · Xiang Wang1 Received: 22 February 2020 / Accepted: 25 April 2020 © The Tunisian Chemical Society and Springer Nature Switzerland AG 2020
Abstract With the objective to explore the modification effects of alkali metals on SnO2 and design more feasible catalysts, Cs/SnO2 samples possessing varied cesium loadings were fabricated for the first time for OCM reaction. It has been demonstrated by XRD, Raman and H2-TPR that the Cs-related species are dispersed highly on the SnO2 support surface instead of doping into the SnO2 lattice or forming surface cesium stannate. Due to the interfacial interaction between SnO2 support and the surface cesium related species, more active oxygen species, such as O22− and O2− anions, are formed, whose amount depends on the cesium loading. As a result, the OCM performance of Cs/SnO2 is evidently enhanced. In conclusion, the quantity of the surface active oxygen sites determines the OCM performance of the catalysts. Keywords Oxidative coupling of methane · Tin oxide · Cesium loading effect · Surface O22− and O2− sites · Interfacial interaction
1 Introduction OCM is a reaction for producing directly value-added hydrocarbons, such as, ethane and ethylene, from the simplest hydrocarbon methane. It has been attracting great interest over the past decades, but remains still great challenge for industrialization because the limited yield of C2 products, due to the thermodynamically favorable formation of CO and CO2 [1–3]. It is commonly accepted that the formation of C2 products in the OCM process follows these steps: (1) the rapture of a C–H bond in methane molecules on the surface active sites of a catalyst, such as reactive O2−, O22−, O− and O2− anions, and basic sites to generate methyl radicals; (2) two methyl radicals couple with each other homogeneously in gas phase to produce ethane, which will be further dehydrogenated to ethylene [1–3]. Since the pioneering work in the early 1980s, numerous efforts have been made to seek for a high performance catalyst [4, 5]. Among the Junwei Xu and Yameng Liu contributed equally to this work. * Xiang Wang [email protected] 1
Key Laboratory of Jiangxi Province for Environment and Energy Catalysis, College of Chemistry, Nanchang University, Nanchang 330031, PR China
tested catalysts, researchers have paid close attention to the following four categories: (1) alkaline earth metal oxides modified by alkali metals, such as Li/MgO, Na/CaO and Ba/MgO [6–9]; (2) pure or modified lanthanide oxides, such as La2O3, Sm2O3, Y2O3 and CeO2 [10, 11]; (3) compound oxides such as A BO3 perovskites or A 2B2O7 pyrochlores [12–14]; (4) Mn/Na2WO4/SiO2 and its modified catalysts [15–17]. However, these catalysts still face technical drawbacks. For instance, Li/MgO exhibits high C H4 conversion and C2 yield at relatively low temperat
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