A study on active sites of A2BO4 catalysts with perovskite-like structures in oxidative coupling of methane

A+1Nb5+O3 (A = Li, Na, K) Perovskites with Different Fine Structures for Oxidative Coupling of Methane: Tracing the Crystalline Phase Effect on the Surface Active Sites

“…As reported, HCO 3 − species is formed by a combination of −OH groups on the catalyst surface with CO 2 , 57 monodentate carbonate is formed by a combination of surface lattice O 2− with CO 2 . 37,57 Bidentate carbonates are generated by the simultaneous bonding of CO 2 to the oxygen and metal sites through both its carbon and oxygen atom ends. 37,57 Bridging carbonate is formed by the combination of surface lattice O 2− and oxygen vacancy of the catalysts with CO 2 .…”

“…37,57 Bidentate carbonates are generated by the simultaneous bonding of CO 2 to the oxygen and metal sites through both its carbon and oxygen atom ends. 37,57 Bridging carbonate is formed by the combination of surface lattice O 2− and oxygen vacancy of the catalysts with CO 2 . 37 It has been reported that CO 2 adsorbing relates to the surface defects, M + −O − ion pairs and unsaturated surface O 2− anions.…”

“…37,57 Bridging carbonate is formed by the combination of surface lattice O 2− and oxygen vacancy of the catalysts with CO 2 . 37 It has been reported that CO 2 adsorbing relates to the surface defects, M + −O − ion pairs and unsaturated surface O 2− anions. 59,60 The weak basic sites are attributed to surface −OH groups, the moderate basic sites are assigned to M + −O − ion pairs and oxygen vacancies, and the strong basic sites are ascribed to the unsaturated surface lattice O 2− anions.…”

“…In addition, bridging carbonate can be observed as well. As reported, HCO 3 – species is formed by a combination of −OH groups on the catalyst surface with CO 2 , monodentate carbonate is formed by a combination of surface lattice O 2– with CO 2 . , Bidentate carbonates are generated by the simultaneous bonding of CO 2 to the oxygen and metal sites through both its carbon and oxygen atom ends. , Bridging carbonate is formed by the combination of surface lattice O 2– and oxygen vacancy of the catalysts with CO 2 . It has been reported that CO 2 adsorbing relates to the surface defects, M + –O – ion pairs and unsaturated surface O 2– anions. , The weak basic sites are attributed to surface −OH groups, the moderate basic sites are assigned to M + –O – ion pairs and oxygen vacancies, and the strong basic sites are ascribed to the unsaturated surface lattice O 2– anions .…”

“…It was reported that those chemisorbed oxygen species (O 2 – , O 2 2– , O – ) and surface lattice O 2– can activate the C–H bonds of CH 4 , which is a vital step for OCM reaction. , Depending on the chemical compositions of different perovskites, various surface oxygen species could function for the reaction. For perovskite catalysts with alkaline earth metals as the A-site cations, the chemisorbed O 2 – , O 2 2– and O – are regarded as the OCM reactive oxygen species. ,, Nevertheless, Jung et al have studied perovskite catalysts for OCM reaction. ,− They found that the oxygen ion conductivity is intimately related to its methane conversion for a perovskite catalyst, which is determined by the structure factors, including the tolerance factor and the cell free volume. Hence, the surface lattice O 2– with moderate binding energies is active for C 2 formation .…”