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

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 degrees 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 degrees 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.

Automated summary

In this study, the surface acidity-basicity of NaZSM-5 was adjusted by simple impregnation in Fe3+ solution, leading to successful dehydration of methanol at lower reaction temperature with a conversion rate of over 90% and a selectivity of 100%. The acidic and basic sites on the catalyst surface were identified as the active sites, and the methanol adsorption behavior revealed the catalytic role of the acid-base balance. Furthermore, the catalyst showed super high stability without coke generation after continuous running for 500 hours.