Effect of microwave radiation on Fe/ZSM-5 for catalytic conversion of methanol to hydrocarbons (MTH)

Abstract

The effect of microwave radiation on the prepared 0.5Fe/ZSM-5 catalysts as a post-synthesis modification step was studied in the methanol-to-hydrocarbons process using the temperature-programmed surface reaction (TPSR) technique. This was achieved by preparing a series of 0.5Fe/ZSM-5 based catalysts under varying microwave power levels (0–700 W) and over a 10 s period, after iron impregnating the HZSM-5 zeolite (Si/Al = 30 and 80). Physicochemical properties were determined by XRD, SEM, BET, FT-IR, C3H9N-TPSR, and TGA techniques. It was found that microwave radiation induced few changes in the bulk properties of the 0.5Fe/ZSM-5 catalysts, but their surface and catalytic behavior were distinctly changed. Microwave radiation enhanced crystallinity and mesoporous growth, decreased coke and methane formation, decreased the concentration of Brønsted acidic sites, and decreased surface area and micropore volume as the microwave power level was increased from 0 to 700 W. From the TPSR profiles, it was observed that microwave radiation affects the peak intensities of the produced hydrocarbons. Application of microwave radiation shifted the desorption temperatures of the MTH process products over the HZSM-5(30) and HZSM-5(80) based catalysts to lower and higher values respectively. The MeOH-TPSR profiles showed that methanol was converted to DME and subsequently converted to aliphatic and aromatic hydrocarbons. It is reasonable to suggest that microwave radiation would be an essential post-synthesis modification step to mitigate coke formation and methane formation and increase catalyst activity and selectivity.