Selective conversion of methanol to monocyclic aromatics via catalysis relay

Abstract

The reliance on methanol as an alternative and sustainable source to produce monoaromatics is challenged by many side reactions. Although the strategy of intentionally incorporating a number of active functionalities (metals and acid sites) in individual catalyst particles can enhance product selectivity, it promotes undesired hydrogen-transfer reactions leading to paraffins and the formation of polyaromatic species causing catalyst deactivation. Here, we report a catalysis relay strategy to control the chemistry by activating methanol differently. Methanol is selectively converted to formaldehyde and light olefins, which follow Prins and Diels-Alder reactions to yield monoaromatics. High selectivity is achieved by the precise location of active sites of different nature in a reactor. The catalyst, which is a combination of inexpensive and commercial ZnO, HZSM-5 and a Zn-ion exchanged HZSM-5, achieves aromatic selectivities of 71.4% initially and above 40% after a 400-h test with full methanol conversion, showing potential for industrial application. In addition, monocyclic aromatics make up nearly all (99%) the liquid products, and BTX (benzene, toluene, and xylenes) account for 91% of monoaromatics, which is advantageous for product separation. This work provides a sound approach to balance product selectivity and catalyst stability via catalysis relay for complex heterogeneous catalytic processes.