Evaluating the influence of diatomaceous earth support and catalyst characterization on nickel-based catalysts for catalytic cracking of polypropylene pyrolysis oils toward fuel production

• NiO/DE catalyst upgrades polypropylene pyrolysis oil, increasing gasoline-range hydrocarbon yields. • Raising NiO loading from 2% to 10% boosts fuel gas yield demonstrating optimized conversion efficiency. • BET and SEM/XRD characterization confirm a high surface area (m²/g), uniform NiO dispersion, and enhanced pore structure, resulting in improved mass transfer and accessibility of catalytic sites. • Synergistic effects between NiO and the porous DE support lead to higher energy density • This integrated approach produces fuels with properties approaching commercial gasoline, demonstrating NiO/DE’s potential as a scalable, sustainable catalyst for upgrading plastic waste. This study investigates the catalytic upgrading of polypropylene pyrolysis oils to liquid fuels using nickel oxide-impregnated diatomaceous earth (NiO/DE) as a novel, affordable catalyst. Post-consumer polypropylene waste was pyrolyzed in a semi-continuous fixed-bed reactor, and the resulting crude oils underwent catalytic reforming with systematically varied NiO loadings, catalyst-to-oil ratios, and temperatures. Catalysts were synthesized by wet impregnation and characterized using SEM-EDS, XRD, and BET analyses. Product yields and quality were assessed by gravimetric methods; chemical compositions were determined by FTIR and GC-MS, and physicochemical properties were quantified by density, viscosity, and calorific value measurements. Increasing nickel loading, catalyst mass, and reaction temperature shifted product distributions towards lighter, fuel-relevant hydrocarbons, raising gas yields up to 42% and decreasing liquid product densities from 865 to 846 kg/m³, while viscosities and calorific values closely matched commercial gasoline standards. FTIR and GC-MS confirmed the selective removal of oxygenated compounds and enrichment of the oils in alkanes and aromatics. The synergy between NiO active sites and the porous structure of diatomaceous earth enhanced catalytic cracking, mass transfer, and deoxygenation, resulting in upgraded fuels with improved energy density and stability. These findings highlight NiO/DE as a robust catalyst for transforming polypropylene waste plastics into high-quality fuels, advancing sustainable waste valorization and supporting circular economy objectives.