Constructing Y<sub>2</sub>B<sub>2</sub>O<sub>7</sub> (B = Ti, Sn, Zr, Ce) Compounds to Disclose the Effect of Surface Acidity–Basicity on Product Selectivity for Oxidative Coupling of Methane (OCM)
Junwei Xu, Rong Xi, Ying Gong, Xianglan Xu, Yameng Liu, Xusheng Zhong, Xiuzhong Fang, Xiang Wang
Abstract
To investigate the influence of surface acidity and basicity on the OCM reaction, four pure-phase Y2B2O7 (B = Ti, Sn, Zr, Ce) compounds have been purposely constructed. The exquisite phase structure change results in the generation of different amounts of surface active O2– and O– sites, which affects CH4 molecule activation. Furthermore, both Lewis acidic sites and basic sites are formed on the catalysts in different amounts, which are related to the lattice disorder extent and the choice of A- and B-site elements. It is elucidated with strong evidence that the surface basic sites are favorable to C2 product selectivity, but the surface acidic sites lead to deep oxidation of CH4 and the coupling products to form COx. To design and fabricate Y2B2O7 catalysts with better C2 product selectivity for the reaction, a disordered defect fluorite structure should be engineered with A- and B- site elements having appropriate basicity.