The effect of doping and steam treatment on the catalytic activities of nano-scale H-ZSM-5 in the methanol to gasoline reaction

In the transformation of methanol to gasoline （MTG）, the selectivity to gasoline and the aromatic content in the produced gasoline are important factors. The catalytic activities of steam-treated and non-steam-treated nano-scale H-ZSM-5 （NHZ5） catalysts impregnated with Ag（I）, Zn（II） or P（V） have been investigated in a continuous flow fixed bed reactor. The NH3-TPD results showed that after impregnation, the Ag/NHZ5, Zn/NHZ5 and P/NHZ5 catalysts contained comparatively more strong, medium-strong and weak acid sites, respectively. Treatment with steam decreased the number of acid sites in all the catalysts, but the pore volumes in the catalysts were larger which improved carbon deposition resistance resulting in prolonged lifetimes. After 6 h of MTG reaction, the selectivity to gasoline for the steam-treated catalysts, Agrho/NHZ5, ZnH2o/NHZ5 and PH2o/NHZ5 were 70.5, 68.4 and 68.7 wt-%, respectively, whereas their respective aromatic contents in the produced gasoline were 61.9, 55.4 and 39.0 wt-%. Thus Pn2o/NHZ5 is the most promising catalyst for MTG applications which can meet the China IV gasoline standard that the amount of aromatics in gasoline should be less than 48 wt-%.