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<p>The selective production of high-value para-xylene (PX) through CO<sub>2</sub> hydrogenation-coupled toluene methylation represents a promising strategy for sustainable carbon utilization. Herein, we report a ZnZrO<sub>x</sub> &amp; HMCM-22 tandem catalyst that integrates CO<sub>2</sub> 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 ZnZrO<sub>x</sub> and transferred to HMCM-22, act as kinetically favored methylating intermediates, enabling direct coupling between CO<sub>2</sub> 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.</p>

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CO2 hydrogenation toward toluene methylation for selective para-xylene synthesis

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月24日

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  • Junqi Tian,
  • Yongjie Xi,
  • Jianian Cheng,
  • Jieyun Zhang,
  • Hao Wang,
  • Fujun Ren,
  • Jun Yuan,
  • Changxin He,
  • Hongfang Yang,
  • Chengyuan Liu,
  • Zelong Li,
  • Can Li

摘要

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.