Atomically dispersed SrOx species on exposed {222} facets of pyrochlore La2Zr2O7 nanocrystals for boosting low-temperature oxidative coupling of methane

The efficient catalysts of strontium oxide (SrOx) supported on exposed {222} facets of pyrochlore La2Zr2O7 nanocrystals (SrOx/LZO-Y) were elaborately synthesized by incipient wetness impregnation method. The introduction of atomically dispersed SrOx species on La2Zr2O7 surface can increase the amount of surface oxygen vacancies induced by Sr2+ substitution of La3+ cations, and the increasing of moderate surface alkaline sites are beneficial to enhance catalytic performance for oxidative coupling of methane (OCM). The SrOx/LZO-Y catalysts have super catalytic performance during low-temperature OCM reaction. SrOx/LZO-12 catalyst with the highest concentrations of O-2(-) species exhibits the highest activity and the lowest apparent activation energy (84 kJ mol(-1)) during low-temperature OCM into C2H4 and C2H6 (C-2) products, i.e., its CH4 conversion, selectivity and yield of C-2 products at 600 degrees C are 30.5 %, 47.4 % and 14.5 %, respectively, and its ratio of C2H4/C2H6 products is 0.77. Based on the results of multiple experimental characterizations, the mechanism of SrOx/LZO-Y catalysts for OCM reaction is proposed: the surface alkaline active centers (O-2(-)) induced by doping of Sr ions can promote the critical step of CH4 activation significantly during low-temperature OCM reaction. It is a new strategy to develop the low-temperature and high-activity catalysts for OCM in practical application.