CO2 hydrogenation toward toluene methylation for selective para-xylene synthesis

The selective production of high-value para-xylene (PX) through CO2 hydrogenation-coupled toluene methylation represents a promising strategy for sustainable carbon utilization. Herein, we report a ZnZrOx & HMCM-22 tandem catalyst that integrates CO2 hydrogenation with shape-selective toluene methylation. The optimized catalyst achieves 91% xylene selectivity with 70.4% PX dominance at 10.3% toluene conversion. Controlled tetraethyl orthosilicate (TEOS) deposition passivates Brønsted acid sites in HMCM-22 supercages, suppressing toluene disproportionation while preserving methylation activity in sinusoidal channels. Mechanistic studies reveal that formaldehyde species, generated on ZnZrOx and transferred to HMCM-22, act as kinetically favored methylating intermediates, enabling direct coupling between CO2 hydrogenation and toluene methylation. This pathway outperforms conventional methanol-mediated routes in both activity and selectivity. Our work establishes a dual-optimization strategy—zeolite microenvironment engineering and reactive intermediate control—offering mechanistic insights and design principles for high-performance tandem catalysis in carbon recycling aromatic synthesis. The selective production of para-xylene via CO₂ hydrogenation coupled with toluene methylation offers a promising route for sustainable carbon utilization. Here, the authors introduce a tandem catalyst that combines efficient CO₂ hydrogenation with shape-selective toluene methylation, achieving 91% xylene selectivity at a toluene conversion of 10.3%.