Developing reactive catalysts for low temperature oxidative coupling of methane: On the factors deciding the reaction performance of Ln2Ce2O7 with different rare earth A sites

To develop more efficient catalysts that can be operated at low temperature region for oxidative of methane (OCM), a series of Ln(2)Ce(2)O(2) compounds with different A sites (Ln = La, Pr, Sm and Y) have been prepared. It is revealed by XRD and Raman techniques that a defective cubic fluorite phase has been formed in all the catalysts. As a consequence, all the Ln(2)Ce(2)O(2) catalysts possess much stronger surface basicity and more abundant electrophilic oxygen species in comparison with individual CeO2, which is beneficial to OCM reaction. It is believed that the concerted interaction between surface intermediate basic sites and selective electrophilic oxygen species is the predominant reason controlling the reaction performance of the catalysts. Furthermore, Ln(2)Ce(2)O(2) catalysts own more abundant mesopores and higher surface areas than pure CeO2, which could also be favorable for the contacting of the reactants with the active sites. Due to the optimal synergistic interaction of these factors, La2Ce2O2 exhibits the best performance among all the catalysts, on which the highest C-2 yield of 16.6% is achieved at 750 degrees C. In comparison with Mn/Na2WO4/SiO2, the most promising catalyst at present, La2Ce2O2 display much improved reaction performance at low temperature region (<750 degrees C).