Effect of metal on the methanol to aromatics conversion over modified ZSM-5 in the presence of carbon dioxide

Abstract

To improve the aromatics yield of methanol to aromatics conversion (MTA) over zeolite, which has become a potential route for producing aromatics, modified ZSM-5 catalysts with equimolar metals denoted as EM-X/ZSM-5 (X = Zn, Cu, Ag, and Ni) were investigated under CO₂ and N₂ flow for MTA in a fixed-bed reactor. The physicochemical properties were characterized by atomic absorption spectroscopy (AAS), N₂ adsorption–desorption isotherms, X-ray diffraction (XRD), and NH₃ temperature-programmed desorption (NH₃-TPD). Comparison with the results obtained in pure N₂ flow showed that catalysts doped with Zn, Ni, and Ag could promote aromatization activity and BTX yield in the presence of CO₂. Among these, EM-Zn/ZSM-5 showed an aromatics yield of 59.05%, with an increase of 8.1%, whereas EM-Cu/ZSM-5 was found to reduce the aromatization activity in the presence of CO₂. Moreover, the interaction mechanism of the active sites of the catalysts with CO₂ for the MTA reaction was explored on the basis of the absorbability of the catalysts for CO₂, which was studied by CO₂ temperature-programmed desorption (CO₂-TPD); the activation ability for CO₂ to combine with hydrogen was investigated by the catalytic reaction of CO₂ + H₂, and the verification experiments for the coupling behavior of ZSM-5 doped with different contents of Zn in the presence of CO₂ were carried out.