Oxidative coupling of methane over alkali halide- promoted perovskite oxide catalysts

Comparing BaZrO3 Perovskite and La2Zr2O7 Pyrochlore for Oxidative Coupling of Methane (OCM): The Importance of Basic Sites vs Oxygen Vacancies

“…6 Using NaCl to modify PbTiO 3 was also reported to enhance the reaction performance. 7 The C 2 yield of the perovskite-type composite oxide catalyst mentioned in these two examples is nearly comparable to that of the most promising Mn/ Na 2 WO 4 /SiO 2 catalyst, but the reaction temperatures are still high. 8 In contrast, A 2 B 2 O 7 composite oxides often exhibit superior low-temperature reaction performance.…”

“…ABO 3 perovskite and A 2 B 2 O 7 pyrochlore-type composite oxides are stoichiometric compounds with simple and definite structures, which exhibit good OCM reaction performance. , The properties of these two types of compounds meet the basic reactive site requirement of the OCM reaction, that is, good thermal stability, an appropriate number of basic sites, a certain number of oxygen vacancies, and excellent oxygen ion mobility. − For example, by doping SrTiO 3 and Sr 2 TiO 4 with different ions, the OCM reaction performance of these two perovskites has been promoted . Using NaCl to modify PbTiO 3 was also reported to enhance the reaction performance . The C 2 yield of the perovskite-type composite oxide catalyst mentioned in these two examples is nearly comparable to that of the most promising Mn/Na 2 WO 4 /SiO 2 catalyst, but the reaction temperatures are still high .…”

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 previously reported, the OCM reaction performance on perovskites is influenced by surface A/B-site molar ratios, preparation methods, heterovalent cation doping, and modification with metal oxides and halides. ,− Ding et al found that the surface enrichment by A-site elements on the ABO 3 compounds can improve the OCM performance, but the enrichment of the B-site elements leads to the complete oxidation of methane . Wu et al adjusted the surface chemical compositions of SrTiO 3 and found that the surface enrichment of Sr increased the methane conversion and C 2 product selectivity.…”

“…26 Yamamura et al observed that the reaction performance of PbTiO 3 can be significantly improved by surface modification with NaCl, and a C 2 product yield of 28.2% was obtained at 750 °C. 27 Jiang et al found that surface doping of Na + on LaMnO 3 as an oxygen carrier can improve the Mn 4+ /Mn 3+ ratio and the oxygen vacancy amount, hence, generating a lot of surface O α− (0 < α < 2). This oxygen species is beneficial to C 2 hydrocarbon formation.…”

“…They found that the doping of alkali and alkaline earth metals with lower valence states can increase the surface oxygen vacancy concentration, thereby enhancing the reaction activity . Yamamura et al observed that the reaction performance of PbTiO 3 can be significantly improved by surface modification with NaCl, and a C 2 product yield of 28.2% was obtained at 750 °C . Jiang et al found that surface doping of Na + on LaMnO 3 as an oxygen carrier can improve the Mn 4+ /Mn 3+ ratio and the oxygen vacancy amount, hence, generating a lot of surface O α– (0 < α < 2).…”