Ca and Sr co-doping induced oxygen vacancies in 3DOM La_2-xSr_xCe_2-yCa_yO_{7- catalysts for boosting low-temperature oxidative coupling of methane}

It is urgent to develop catalysts with application potential for oxidative coupling of methane (OCM) at relatively lower temperature. Herein, three-dimensional ordered macroporous (3DOM) La2-xSrxCe2-yCayO7-delta (A(2)B(2)O(7)-type) catalysts with disordered defective cubic fluorite phased structure were successfully prepared by a colloidal crystal template method. 3DOM structure promotes the accessibility of the gaseous reactants (O-2 and CH4) to the active sites. The co-doping of Ca and Sr ions in La2-xSrxCe2-yCayO7-delta catalysts improved the formation of oxygen vacancies, thereby leading to increased density of surface-active oxygen species (O-2(-)) for the activation of CH4 and the formation of C-2 products (C2H6 and C2H4). 3DOM La2-xSrxCe2-yCayO7-delta catalysts exhibit high catalytic activity for OCM at low temperature. 3DOM La1.7Sr0.3Ce1.7Ca0.3O7-delta catalyst with the highest density of O-2(-) species exhibited the highest catalytic activity for low-temperature OCM, i.e., its CH4 conversion, selectivity and yield of C-2 products at 650 degrees C are 32.2%, 66.1% and 21.3%, respectively. The mechanism was proposed that the increase in surface oxygen vacancies induced by the co-doping of Ca and Sr ions boosts the key step of CH bond breaking and CC bond coupling in catalyzing low-temperature OCM. It is meaningful for the development of the low-temperature and high-efficient catalysts for OCM reaction in practical application. (c) 2024 cience Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.