Bifunctional WOx/SiO2 catalysts for hydrogen-free upgrading of B100 and bio-ethylene to SAF and green diesel precursors via olefin metathesis and deoxygenation

Abstract

This work presents a hydrogen-free catalytic route for upgrading palm-derived biodiesel (B100) into olefinic precursors for sustainable aviation fuel (SAF) and green diesel (GD) using bifunctional WOx/SiO2 catalysts under atmospheric pressure. The catalysts integrate olefin cross-metathesis, mediated by surface W CH2 species, with deoxygenation via Lewis-acidic W O sites, enabling selective C C bond exchange and C O bond cleavage without external hydrogen or noble metals. Detailed mechanistic studies revealed that methyl oleate (MO) rapidly undergoes cross-metathesis with ethylene to yield SAF-range C9–C14 precursors, while methyl palmitate (MP) contributes primarily to GD (C15–C18) through ketene intermediates and decarbonylation–hydrogen transfer pathways. Contact time and temperature experiments confirmed that MO conversion is kinetically favored at milder conditions, whereas MP-derived pathways dominate at higher temperatures and extended residence times. Catalyst loading studies show that the 3 and 5 wt% WOx/SiO2 catalysts are dominated by highly dispersed isolated and polymeric WOx species, which exhibit higher accessible acidity and consequently promote secondary cracking reactions. In contrast, the 8 wt% WOx/SiO2 catalyst contains a higher fraction of bulk crystalline WO3 domains, resulting in reduced surface acidity and suppressed cracking. Overall, 8 wt% WOx/SiO2 delivers reasonable rates with high selectivity toward SAF/GD precursors, while minimizing secondary cracking. It can be regenerated and recycled with substantial recovery of catalytic performance, establishing a robust, low-pressure, and hydrogen-free pathway for scalable renewable fuel production from B100.