Rare earth metal modified CaO catalysts Ln/CaO (Ln=La, Ce, Nd) for oxidative coupling methane: Revealing the interaction between metal oxide and carrier

Abstract

Herein, a series of rare earth metal-modified alkaline earth metal oxide CaO Ln/CaO (Ln=La, Ce, Nd) catalysts were synthesized by sol-gel method and used for OCM reaction. Their reaction performance is not solely influenced by rare earth oxide and carrier CaO, but rather by their interaction. Specifically, the interaction between rare earth oxide and the CaO carrier can increase the surface basicity, the amount of strong basic sites and reactive oxygen species O₂^-, thereby further enhancing the catalytic performance compared to rare earth oxide and the CaO carrier. In addition, the basicity of rare earth oxides affects the concentration of oxygen vacancies in the modified catalyst. The stronger the basicity of rare earth oxides, the more abundant the concentration of oxygen vacancies generated by their interaction with the carrier. The DFT calculation results indicate that the Ln/CaO (100) surface is conducive to the generation of O₂^-, which easily activates methane to produce methyl radicals, and then desorb into the gas phase and couple to form C₂H₆.