Design of strontium stannate perovskites with different fine structures for the oxidative coupling of methane (OCM): Interpreting the functions of surface oxygen anions, basic sites and the structure–reactivity relationship

Abstract

To seek more feasible catalysts for OCM reaction, SrSnO3, Sr2SnO4 and Sr3Sn2O7 perovskite compounds have been purposely designed and synthesized. It is discovered that the fine crystal structure change influences the reaction performance of the catalysts significantly, which follows the order of Sr2SnO4 > Sr3Sn2O7 > SrSnO3.On these perovskite catalysts, both the electrophilic chemisorbed O2–/O22– and surface lattice O2– species are active and selective for C2 product formation. In addition, both of their moderate and strong surface basic sites contribute vitally to the reaction. It is found that the moderate sites are associated with the M+−O- ion pairs and oxygen vacancy, and the strong basic sites are related to the coordinatively unsaturated surface lattice O2–. Due to the phase structure difference of the three perovskites, their Sn-O bond length changes in the order of Sr2SnO4 > Sr3Sn2O7 > SrSnO3. Furthermore, both the electrical conductivity and DFT calculation results have testified that it is easier for Sr2SnO4 to generate surface oxygen vacancies than Sr3Sn2O7 and SrSnO3, which explains that this sample has the largest quantities of active surface oxygen and basic sites, as well as the best OCM performance.