Red Mud-Supported Ni and Co Catalysts for Hydrodeoxygenation of Palmitic Acid: Insights into Reaction Pathway, Product Selectivity, and Catalyst Recyclability

Understanding the hydrodeoxygenation (HDO) of linear chain fatty acids is crucial for the conversion of waste oils and biomass into sustainable aviation fuels. In this study, red mud, a byproduct of bauxite ore processing, was used as a support material for Ni and Co metals. X-ray diffraction (XRD) confirmed the impregnation of metals, and X-ray photoelectron spectroscopy (XPS) analyzed their electronic states. Catalyst performance was evaluated by HDO of palmitic acid, studying the effects of catalyst type, temperature, time, and hydrogen pressure on the selectivity and conversion. At 240 °C, 5 MPa, and 4 h, high selectivity for hexadecanol (10%) and hexadecane (87%) was obtained, and hence, the catalyst recycle at this condition was observed up to 5 cycles. Optimal operating conditions shifted the pathway from decarboxylation (DCX) to HDO. Lower temperatures and pressures favored hexadecanol, while hexadecane formation was favorable at higher pressures. Fourier Transfer Infrared spectroscopy (FTIR), XRD, XPS, thermogravimetric analysis (TGA) indicated coke formation after recycling.