Catalytic Reforming of Lignite Pyrolysis Volatiles over Metal Oxide and Zeolite Tandem Catalysts for Light Aromatics Production
Pyrolysis is a key route for the graded conversion of low-rank coal, yet the volatiles are rich in oxygenates and heavy components, limiting direct utilization. This study proposes a tandem catalytic system combining metal oxides and ZSM-5 zeolite to efficiently convert lignite pyrolysis volatiles into light aromatics (benzene, toluene, ethylbenzene, xylene, naphthalene, methylnaphthalene). The upper-layer metal oxide pre-cracks large molecules and removes oxygenates, reducing carbon deposition on the zeolite and extending catalyst life. Among metal oxides tested, strongly basic MgO exhibited superior cracking and deoxygenation performance. Compared to ZSM-5 alone, the MgO/ZSM-5 tandem system increased total light aromatics yield by approximately 20% to 21.5 mg/g, while maintaining liquid product proportion at 21.4%. The incorporation of MgO also significantly reduced coke deposition on ZSM-5, preserving its catalytic activity and potentially prolonging its operational lifespan. These findings provide a theoretical basis for upgrading low-rank coal pyrolysis volatiles to valuable light aromatics.