Effect of calcination temperature on MnFeCoNiCu/activated carbon catalysts for hydrodeoxygenation of fatty acid methyl esters to bio-jet fuel and green diesel

As sustainable alternatives to fossil fuels, biomass-derived liquid fuels play a critical role in mitigating greenhouse gas emissions and diversifying energy supplies. In this study, the effect of calcination temperature (600–1000 °C) on the structure and catalytic performance of MnFeCoNiCu/activated carbon (AC) catalysts via in-situ carbon reduction method for the hydrodeoxygenation (HDO) of fatty acid methyl esters (FAME) to sustainable biofuels including bio-jet fuel and green diesel was systematically investigated. Results revealed that increasing calcination temperature promoted the transformation of the crystal structure from body-centered cubic (B2) to face-centered cubic (FCC), with the AC-900 catalyst (calcined at 900 °C) exhibiting a dominant FCC phase, enhanced metal dispersion, and optimal surface defect density. Although higher temperature reduced the specific surface area and pore volume of the AC support, the formation of a stable multimetallic solid solution and strong metal-support interactions at 900 °C significantly improved catalytic performance. Under optimal reaction conditions (350 °C, 0 MPa H2, 2 h), the AC-900 catalyst achieved 100% FAME conversion and 97% hydrocarbon selectivity, primarily via decarbonylation/decarboxylation (DCN/DCX) pathways, favoring the production of C15–C17 hydrocarbons aligned with green diesel and bio-jet fuel specifications. Increasing H2 pressure favored alkane formation by promoting olefin hydrogenation, while lower pressure enhanced C–C bond cleavage for shorter-chain hydrocarbons. Circulating stability tests indicated that the AC-900 catalyst maintained 62% FAME conversion and >80% hydrocarbon selectivity after 5 cycle. This work highlights the critical role of calcination temperature in tailoring FCC-structured multimetallic catalysts for efficient FAME conversion, providing insights into the rational design of stable, high-performance catalysts for sustainable biofuel production.