Dual advantages of rapid zeolite channel diffusion and Ni sites: 1Ni/L-DAl zeolite enables efficient polyolefin hydrocracking to liquid fuel

Abstract

Hydrocracking-based upgrading and recycling of polyolefins into high-quality liquid fuels are excellent methods for reducing solid-waste pollution. However, reasonable control of the carbon number distribution of the products and limiting it to the C₈–C₁₆ range remains a huge challenge. Herein, we report a Ni-embedded dealumination-layered pillared (1Ni/L-DAl) zeolite, which enables rapid hydrocracking of low-density polyethylene (LDPE) through the synergistic effect of its mesoporous structure and Ni sites. At 300 °C, under a H₂ pressure of 2 MPa and a reaction time of 1 h, the 1Ni/L-DAl zeolite catalyst enabled the hydrocracking of LDPE with a liquid yield of 87.02% (alkane content, 83.73%) and an LDPE conversion exceeding 99%. The selectivity of products in the C₈–C₁₂ range reached 80.98%, and the selectivity of hydrocarbons in the C₈–C₁₆ range reached 89.81%. The polyolefin macromolecule was strongly adsorbed at the Lewis acid sites of LSP-Z100 zeolite, generating carbocation intermediates that underwent further isomerization and β-scission. Molecular dynamics (MD) simulations demonstrated that the zeolite's unique mesoporous structure significantly accelerated the diffusion of olefin molecules, which was key to the narrow product distribution achieved by the 1Ni/L-DAl zeolite catalyst. Density functional theory (DFT) calculations demonstrated that rapid diffusion of olefin molecules to Ni sites followed by hydrogenation to alkanes represented the most favorable pathway. The 1Ni/L-DAl zeolite also achieved competitive conversion efficiency in the hydrocracking of polyolefin waste from daily life (including even agricultural waste), proving its potential for practical application.