Extending catalyst lifetime through coke mitigation and magnesium-assisted regeneration in low-density polyethylene/biomass co-pyrolysis

Stable catalytic processes are needed to convert waste plastics and biomass into value-added fuels and chemicals, but coke-induced deactivation remains a major limitation for metal-acid zeolite catalysts. In this study, FeNi@HZ50 was modified by introducing Cu or Ca as a second metal to regulate coke evolution, forming 3Cu-FeNi@HZ50 and 3Ca-FeNi@HZ50. Compared with 3Cu-FeNi@HZ50, 3Ca-FeNi@HZ50 exhibited higher selectivity toward monocyclic aromatic hydrocarbons (MAHs), lower polycyclic aromatic hydrocarbon formation, and a weaker hard coke contribution, as revealed by temperature-programmed oxidation. The relative contents of MAHs and benzene, toluene, ethylbenzene, and xylenes (BTEX) in the liquid products over 3Ca-FeNi@HZ50 reached 58.98% and 45.19%, respectively. Moderate Ca loading promoted aromatization and suppressed deep condensation, whereas excessive Ca partially covered metal or acid sites and increased the retention of oxygenates and aliphatics. Under continuous feeding conditions, 3Ca-FeNi@HZ50 showed slower BTEX decay, less accumulation of heavy components, and weaker coke formation than FeNi@HZ50. To facilitate reuse, a magnesium-assisted regeneration process was developed by impregnating the deactivated catalyst with Mg before reactivation. This treatment improved micropore accessibility, shifted deposits toward more easily removable species, and enhanced cyclic stability. These findings establish an engineering-oriented strategy for extending the lifetime of metal-acid zeolite catalysts by coupling coke mitigation with regeneration reinforcement in catalytic co-pyrolysis.