Modulating reaction pathways for the highly selective production of light aromatics from CO2 hydrogenation

Abstract

Direct CO₂ hydrogenation to high-value light aromatics (BTX) has garnered significant research interest, but the current state-of-the-art BTX selectivity remains unsatisfactory. Herein, an oxide/dual-zeolite tandem catalyst was developed through physical mixing of SAPO-34 (hereafter abbreviated as SP34) and ZnZrO_x/ZSM-5 (hereafter referred to as ZZO/Z5). The optimized ZZO/2SP34/Z5 catalyst achieves a promising BTX selectivity (42.3% of aromatics), while maintaining a high CO₂ conversion (12.4%) and overall aromatic selectivity (75.3%, CO-free) at a relatively low temperature of 320 °C. By introducing the SP34 zeolite, the adsorption capacity of the ZZO/Z5 catalytic system for H and CO₂ is enhanced. Probe experiments and in situ DRIFTS spectra indicate that the SP34 component converts part of the methanol into light olefins, thereby reducing the concentration of oxygenated intermediates directly transferred to Z5 and inhibiting the surface methylation of BTX into C₉₊ aromatics. Compared with particle mixing and multi-bed mixing, proximate grinding mixing proves to be the optimal mixing method, facilitating the selective formation of BTX at 3 MPa and 1200 mL/(g_cat·h). Comparative experiments demonstrate that this dual-zeolite strategy is more facile and effective than the traditional passivation of external acid sites. Notably, such high BTX selectivity achieved by the ZZO/2SP34/Z5 catalyst at 320 °C has rarely been reported in the literature. This work provides an efficient non-petroleum pathway for the highly selective production of BTX and offers valuable insights into the reaction mechanisms associated with the two pathways of direct CO₂ hydrogenation to aromatics.