High-Efficiency Conversion of Methanol to BTX Aromatics Over a Zn-Modified Nanosheet-HZSM-5 Zeolite

A Zn-modified nanosheet-HZSM-5 zeolite Zn-SH-HZSM-5) was prepared and tested as a catalyst in the methanol-to-aromatics (MTA) reaction. First, both an effective suppression of C9+, aromatics formation and a significantly enhanced yield of benzene, toluene, and xylene (BTX) aromatics were achieved by reasonably controlling the reactive pathways in this catalytic reaction system. Further alkylation of BTX aromatics to form C9+ byproducts was effectively limited by the significantly reduced retention time of BTX molecules in the micropore system, with a significantly shortened diffusion-reaction path. Furthermore, the conversion of methanol to BTX was significantly improved by introducing new surface Zn-Lewis acid sites, achieving a synergistic catalysis with Bronsted acid sites. Second, this catalyst also exhibited strong capabilities both to limit the formation and deposition of large-size coke molecules, thanks to its shortened diffusion-reaction path, and to accommodate carbon, due to the high external surface area and considerable stacking mesopores. As a result, our Zn-SH-HZSM-5 catalyst demonstrated good stability in a 100 h on-stream reaction, providing a BTX yield higher than 54.5%, with a C9+ aromatic byproduct formation lower than 5.1%. The present work may provide a promising way for developing an elegant catalyst for a more sustainable MTA process.