Dissecting La2Ce2O7 catalyst to unravel the origin of the surface active sites devoting to its performance for oxidative coupling of methane (OCM)

• Published in: Catalysis today 2022-09, Vol.400-401, p.73-81
• Main Authors: Zhang, Zhixuan, Gong, Ying, Xu, Junwei, Zhang, Yan, Xiao, Qiyao, Xi, Rong, Xu, Xianglan, Fang, Xiuzhong, Wang, Xiang
• Format: Article
• Language: English
• Subjects: Catalyst dissection strategy; Disordered defective cubic fluorite; La2Ce2O7 compound; OCM reaction; Origin of surface active sites
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2021.11.012

As an endeavor to trace the origin of the active surface sites on La2Ce2O7 compound for OCM reaction, a dissection strategy is adopted in this work. In detail, the reaction performance of pure La2O3, CeO2, the physical mixture of La2O3 and CeO2 (La2O3 +CeO2), and the combination of pure La2O3 and CeO2 with different orders in the reactor (La2O3-CeO2 or CeO2-La2O3) has been tested for OCM reaction under the same condition. Individual La2O3, CeO2 and their simple mixing/combination display much lower OCM performance than La2Ce2O7 compound, especially below 700 °C. Therefore, the reaction performance of La2Ce2O7 is not due to a simple accumulation of the two pure oxides. To achieve favorable OCM performance, La and Ce cations must be combined into a stable La2Ce2O7 compound possessing a disordered defective cubic fluorite structure with intrinsic oxygen vacancies. In situ Raman, CO2-TPD, EPR and XPS results have demonstrated on the surface of La2Ce2O7, much larger amount of both O2- species and moderate basic sites have been formed in comparison with the individual metal oxides or their simple mixing/combination, thus it exhibits the optimum reaction performance among all the catalysts. [Display omitted]