Enhanced tar upgrading and anti-coking performance of Co-Ce bimetallic-loaded EDTA-modified ZSM-5@activated carbon catalyst

Abstract

The heavy tar components produced during lignite pyrolysis significantly hinder the practical application of coal pyrolysis products due to their high viscosity, low calorific value, and corrosive properties. To improve tar upgrading efficiency and enhance catalyst resistance to carbon deposition, this study developed composite support by combining an EDTA-chelated ZSM-5 molecular sieve with activated carbon. A comprehensive investigation was performed on catalyst systems containing 5 wt% single metals (Co or Ce) and Co/Ce bimetals (total metal loading 5 wt%, Co/Ce mass ratio 1:1). Analyses of catalytic pyrolysis tar and gas products using TG-FTIR and Py-GC/MS demonstrated that the CoCe/C@EZ5 catalyst substantially increased light aromatic selectivity, specifically enhancing the production of high-value BTEXN aromatics (benzene, toluene, ethylbenzene, xylene, and naphthalene) by 47.17 %. Kinetic studies revealed that CoCe/C@EZ5 lowered the activation energy for tar cracking while improving the conversion efficiency of heavy tar components into light aromatics. Characterization through SEM, TEM, XPS, NH₃-TPD, TPO, and Raman spectroscopy confirmed that metal doping achieved simultaneous modulation of surface acid properties, improved redox tolerance, and reduced carbon deposition during reactions, collectively contributing to enhanced catalyst stability. The activated carbon component exhibited two synergistic roles: its hierarchical pore structure effectively adsorbed and dispersed carbon precursors, while oxygen-containing surface groups (e.g., carboxyl and phenolic hydroxyl groups) formed coordination bonds with Co/Ce metal species, thereby improving metal dispersion stability and coking resistance. TPO and Raman spectroscopy analyses demonstrated that incorporating activated carbon alleviated catalyst deactivation caused by carbon deposition, thereby facilitating oxidative removal of the deposited carbon.