Upgrading Trimethylbenzene to Durene by CO₂-Mediated Methylation over Cu-Boosted ZnZrO_<i>x</i> Integrated with HZSM-5

Abstract

Durene is a valuable aromatic hydrocarbon used in making polyimide and aviation kerosene additives, which traditionally rely on unsustainable petroleum sources, leading to high costs and environmental concerns. Herein, we introduce an alternative method for synthesizing durene with high selectivity through trimethylbenzene methylation coupled with CO 2 hydrogenation. Durene selectivity of 83.2% in tetramethylbenzene (TetraMB) and TetraMB selectivity of 69.1% in aromatics were achieved with a 1,2,4-trimethylbenzene conversion of 33.2%. Remarkably, the durene selectivity in TetraMB remained high at 81.4%, even when fed with a mixed trimethylbenzene. The designed composite catalyst 5%CuZnZrO x – HZSM-5 remained active for over 1100 h without significant loss in performance. Further investigations revealed that the role of Cu in the ZnZrO x composite was to provide more active intermediates from the CO 2 hydrogenation, thereby enhancing the methylation of aromatics. Detailed studies of the catalyst structure and reaction kinetics indicated that Cu 0 is essential for generating active *H species, facilitating CO 2 hydrogenation to methoxy, a key intermediate for the methylation of trimethylbenzene.