Regulating surface acid-base balance on NaZSM-5 by Fe modification towards enhanced methanol dehydration to dimethyl ether

Abstract

Mostly, adjusting or modifying the surface acidity by embedding other elements on HZSM-5 is carried out to promote catalytic performance for methanol dehydration. However, the modified HZSM-5 allows to conduct the dehydration reaction at high temperatures (≥ 220 °C), and with lower catalytic activity. In this work, the modification of NaZSM-5 by simple impregnation in Fe3+ solution to adjust its surface acidity-basicity was attempted. The obtained composite was systematically characterized by XRD, SEM, TEM, XPS, UV–vis, 29Si and 27Al MAS NMR, and N2 adsorption-desorption measures, respectively, and it presented high efficiency for dehydration of methanol to dimethyl ether at lower reaction temperature due to the uniform distribution of the active sites and acid-base balance on the surface, achieving >90% conversion with ca. 100% selectivity at 180 °C. The acidic and basic sites as the active ones on the catalyst surface were measured by NH3- or CO2-TPD. The methanol adsorption behavior was explored by in situ IR technique, realizing the associative catalytic role of acidic-basic balance. Moreover, as it continuously runs over 500 h, the catalytic activity and selectivity hold constant without coke generation, indicating its super high stability.