Interplay of bi-metallicity and acidity for the selective oleic acid deoxygenation over Ni/M-based BEA zeolite catalysts towards diesel-range hydrocarbons

This work investigates the synergistic effects of bimetallic character and acidity in 10Ni/5M-Beta catalysts (M = Mn, Fe, Co, Cu) for oleic acid (OA) hydrodeoxygenation (HDO) at 350 and 400 °C. Various analytical and computational techniques were employed to examine the catalysts' intrinsic properties. Structural analysis revealed zeolite beta and metallic Ni structures (10–15 nm) and suggested Ni-M alloy formation in some systems (geometric effect). Co and Mn enhanced surface metal sites, acting as electron donors, while Fe and Cu were electron acceptors, influencing electron transfer at the Ni-support interface, consistent with thermodynamic alloying stability predicted by DFT calculations. Catalyst evaluation demonstrated complete OA conversion with hydrocarbons (HC, C8-C18) produced across all catalysts. The Mn-based catalyst achieved the highest HC yield (24 %), attributed to increased metal site concentrations and a monometallic Ni phase. This doping also enhanced Lewis acid sites, promoting C-C cleavage through DCO/DCO2 pathways. The Ni-Cu alloy promoted the HDO pathway by increasing Brønsted sites, facilitating oxygen groups dehydration and C18 production. At 400 °C, selectivity shifted toward lighter alkanes due to enhanced cracking. DFT showed stable alloy formation for all systems except Mn. Simplified calculations with butyric acid (computationally reasonable carbon number) favored adsorption on Mn-Ni(111), followed by Fe-Ni(111).