Hydrocarbon-Enriched Bio-oil from Catalytic Microwave Pyrolysis of Macaúba Epicarp

Abstract Microwave-assisted pyrolysis (MAP) of Acrocomia aculeata epicarp (EPM) was investigated using an ex situ catalytic configuration supported on silicon carbide (SiC) foams. The study employed acidic, basic, and bifunctional catalysts, including CaO, phosphate rock residue (PO), Nb₂O₅, NiO/Nb₂O₅, and zeolite. The primary objective was to elucidate the catalytic effects on product selectivity, the reduction of oxygenated compounds, and the promotion of hydrocarbons in the resulting bio-oils. Optimization of the non-catalytic pyrolysis indicated that 550°C was the ideal temperature, yielding 48.4% condensables, 20.6% biochar, and 32.3% gases. Among the catalysts tested, the bifunctional NiNb–PO system achieved the highest hydrocarbon fraction (61.3%) and the lowest oxygenated content (35.4%), demonstrating a synergistic interaction between basic and redox sites. Basic catalysts such as CaO and PO enhanced decarboxylation and decarbonylation reactions, while Nb₂O₅ and NiNb-based systems favored selective hydrogenation and deoxygenation. In contrast, zeolite-containing systems exhibited higher acidity and a propensity to form oxygenated intermediates. The resulting biochar presented a high fixed carbon content (up to 42.5%), a low O/C ratio (0.24), and a higher heating value (21.55 MJ kg⁻¹), indicating the formation of an aromatic, porous, and stable carbon matrix suitable for energy and environmental applications. This work demonstrates that integrating multifunctional catalysts, conductive SiC supports, and microwave heating provides a technically viable and environmentally sustainable route for producing hydrocarbon-enriched bio-oils and high-performance biochars from tropical lignocellulosic residues, supporting the advancement of low-carbon bioenergy technologie.