Identification of Active Sites over MCM-49 for Direct Syngas Conversion to Gasoline

Elucidating the catalytic roles of the acid sites in different pore systems of zeolite is of great significance for the optimization of zeolite catalysts but remains a challenge. Herein, we show that the accessibility of the acid sites in different pores of MCM-49 is tuned by sulfuric acid during crystallization, as revealed by positron annihilation lifetime spectroscopy (PALS) and infrared (IR) spectroscopy. This allows the identification of the active sites for selective formation of gasoline in direct syngas conversion over the ZnCrOx -HMCM-49 (oxide-zeolite, OXZEO) catalyst. It reveals that the acid sites in the sinusoidal channels are active for gasoline formation, whereas the acid sites in the supercages favor the production of light paraffins and are also prone to deactivation. This fundamental understanding is essential for further optimization of catalysts for syngas conversion to gasoline.