Zeolite Catalysts for Hydrogen Harvesting from Polyethylene: A Sustainable Approach to Plastic Waste Upgrading

Abstract This study aims to produce hydrogen from polyolefin plastics, using nickel zeolite‐based catalysts under inert conditions. Low density polyethylene (LDPE) has been chosen as a model for upgrading polyolefin plastic wastes. Zeolites with a large variety of physicochemical properties have been investigated including large pores beta (BEA/BEB), faujasite (FAU), mordenite (MOR), and the intermediate pore ZSM‐5 (MFI). All have been impregnated with nickel to enhance catalytic hydrogen production. Their catalytic performance was assessed through LDPE conversion in a fixed bed reactor under nitrogen flow as well as in a combined TGA‐MS setup. All catalysts performed better, that is, at lower temperatures than under thermal decomposition. Ni‐LZY‐210, Ni‐Beta, and Ni‐CBV712 are active at low temperatures (∼250 °C) with a high hydrogen selectivity (40–50 mol.% of the gas phase). They also exhibit different selectivity toward isobutane and heavier hydrocarbons (C6+). The composition of the condensed products depends also of the zeolite: with Ni‐Beta, the primary products are alkyl benzenes (C8‐13), while Ni‐CBV712 produces approximately 30 wt.% of branched alkanes in the C8‐10 range and Ni‐LZY‐210 predominantly yields aromatic compounds in the C8‐10 range. The coke deposit varies also in the range of 2–20 wt%. The presence of nickel is essential for hydrogen production. In the absence of nickel the yield of hydrogen ranges from 1% to 7% for pure zeolite‐based catalysts.