Structure, Acidity, and Catalytic Activity of Mesoporous Acid Catalysts for the Gas-Phase Synthesis of MTBE from MeOH and ButOH

The regular mesostructure of Si–MCM-41 with a uniform mesopore size is well maintained after 50 wt% HPW loading that was highly dispersed onto Si–MCM-41, without an HPW crystalline phase being detected by XRD. An HPW-supported mesoporous catalyst (HPW/MCM-41) shows excellent catalytic activity and on-stream stability for the gas-phase synthesis of MTBE at temperatures below 100°C. The surface acidity and hydrophobicity of the HPW/MCM-41 catalysts are enhanced stepwise by increasing the HPW loading. The ratio of Brønsted acidity to Lewis acidity on HPW/MCM-41 is adjustable by varying the amounts of HPW. The catalytic activity of various mesoporous catalysts showed the following order: Amberlyst-15≈HPW (50%)/MCM-41>H2SO4/MCM-41>HAlMCM-41>SO42−/ZrO2/MCM-41>NaAlMCM-41⪢Si–MCM-41, corresponding to the importance of their surface acidity. The exception of SO42−/ZrO2/MCM-41 in this arrangement may be related to the complexity of sulfated-ZrO2 superacid. The rapid deactivation of the H2SO4/MCM-41 catalyst is ascribed to the leaching of mobile H2SO4 molecules on Si–MCM-41 during the reaction.