Oxidative coupling of methane (OCM) was conducted over LaAlO3_X catalysts that were prepared by a coprecipitation method using different co-precipitation pH values (X=6-10).The aim is to investigate the effect of pH values on the catalytic activity of LaAlO3 catalysts in this reaction.The results showed that the co-precipitation pH value affected greatly on the formation of chemical species of precipitate precursors in the co-precipitation step,leading to different phases of the finally obtained LaAlO3 catalysts.When the co-precipitation pH value increased up to 8,the lanthanum-related phases such as La2O3 and La(OH)3 were gradually formed as by-products,preventing the formation of LaAlO3 perovskite crystalline structure and facilitating the formation of oxygen vacancies on catalyst surface.However,at pH value of 9 or higher,the lanthanum content in the precipitate precursor was increased greatly.Not LaAlO3 perovskite but lanthanum-related phases were developed as main phases,reducing their catalytic activities in this reaction.Among LaAlO3 catalysts,the one prepared at pH =8 showed the highest C2 yield due to its well-developed oxygen vacancies and electrophilic lattice oxygen.Therefore,the co-precipitation pH value strongly affected the LaAlO3 catalyst activity in OCM reaction.A precious pH control should be required to prepare various perovskite catalysts for the OCM.