Carboxylic acid free green fuel production from the pyrolysis of WCO using Ni-based bimetallic catalysts supported on marble waste

Waste cooking oil (WCO) is a potential feedstock for producing renewable hydrocarbon fuels through catalytic pyrolysis. In this work, a Ni-based bimetallic catalyst supported on marble waste (MW) was prepared to convert WCO into hydrocarbon fuel without detectable carboxylic acids. The performance of NiZnMW was compared with those of NiCoMW, NiFeMW, and NiCuMW to evaluate the effect of the second metal on the catalytic activity. The catalysts were characterized using XRD, N₂ adsorption-desorption, SEM-EDX, FESEM, HR-TEM, FTIR, H₂-TPR, CO₂-TPD, XPS, and TGA. Pyrolysis was carried out at 380 °C under a nitrogen atmosphere. Among the catalysts, NiZnMW showed the best performance, with 96.6% WCO conversion, 68.93% hydrocarbon yield, and 92.28% hydrocarbon selectivity. No carboxylic acids were detected in the liquid product. The good performance of NiZnMW is related to the combined effect of Ni and Zn, the presence of basic sites and suitable pore properties, which improve the removal of oxygen-containing compounds during pyrolysis. The catalyst also remained active after four reaction cycles, with hydrocarbon selectivity remaining above 86% after four consecutive cycles. The NiZnMW catalyst prepared from marble waste showed high activity and good stability, making it a practical catalyst for producing hydrocarbon fuel from waste cooking oil.