Upcycling bentonite into nickel sorbent and its subsequent use as a heterogeneous catalyst in CO2-assisted pyrolysis of high-density polyethylene

This study presented a strategy for utilizing sodium aluminosilicate hydrate (NASH), synthesized via alkali activation of bentonite, as a dual-function material for aqueous Ni 2+ removal and subsequent catalytic application in CO 2 -assisted pyrolysis of high-density polyethylene (HDPE). The NASH samples exhibited high Ni sorption capabilities, achieving Ni loadings of 1.0–9.0 wt% through concentration-dependent sorption mechanisms. Subsequent calcination and H 2 reduction successfully converted sorbed Ni II species into metallic Ni 0 , as confirmed by XRD and XPS analyses. Pyrolysis experiments with HDPE revealed that 9.0% Ni-Cat. exhibited the highest catalytic activity, promoting syngas (H 2 and CO) production while effectively suppressing coke formation under a CO 2 atmosphere. Increasing the CO 2 concentration from 20 to 80 vol% progressively enhanced cumulative CO yield from 18.2 to 58.9 mmol, with both H 2 and CO yields reaching their maximum at 80 vol% CO 2 . Overall, this approach offered an integrated strategy for simultaneous spent sorbent upcycling, Ni-contaminated wastewater remediation, and thermochemical plastic waste valorization.