Shape-selective synthesis of para-xylene through tandem CO₂ hydrogenation and toluene methylation over ZnCeZrO_x/MCM-22 catalyst

Selective synthesis of value-added xylenes and para-xylene (PX) by CO₂ hydrogenation reduces the dependence on fossil resource and relieves the environment burden derived from the greenhouse gas CO₂. Herein, modified MCM-22 zeolite combined with ZnCeZrO_x solid solution is reported to catalyze the tandem CO₂ hydrogenation and toluene methylation reaction at a relatively low temperature (< 603 K), showing xylene selectivity of 92.4% and PX selectivity of 62% (PX/X, 67%) in total aromatics at a CO₂ conversion of 7.7%, toluene conversion of 23.6% and low CO selectivity of 11.6%, as well as giving high STY of xylene (302.0 mg·h^–1·g_cat^–1) and PX (201.6 mg·h^–1·g_cat^–1). The outstanding catalytic performances are closely related to decreased pore sizes and eliminated external surface acid sites in modified MCM-22, which promoted zeolite shape-selectivity and suppressed secondary reactions.