Modulation on reaction path and product selectivity by non-metallic P-doped catalysts in hydrodeoxygenation

The microstructure of the catalyst influences the electronic states and acid-base properties, allowing for the selective modulation of the catalytic mechanism and substrate conversion pathways, thereby enhancing the selectivity of the target products. In this work, two catalysts, low P-doped Pd/1.5W-0.125P-SiO₂ and high P-doped Pd/1.5W-1P-SiO₂, were synthesized by tuning the amount of non-metallic phosphorus doping in WO₃-SiO₂. These catalysts exhibited distinct catalytic pathways and product selectivity for the hydrodeoxygenation (HDO) of δ-furfurylidenelevulinic acid (FDLA), a biomass-derived platform molecular condensation intermediate. Comprehensive characterizations revealed that high P doping induced the formation of a WO₃-PO₄ structure, which provided strong Brønsted acid sites. These sites facilitated the cleavage of the C₄-O bond during lactone ring opening and selectively preserved the carboxyl functional group, yielding 56.64 % decanoic acid (DA). By contrast, low P-doped catalysts retained the WO₃ structure rich in Lewis acid sites but lacking Brønsted acid sites, leading to the lactone via hydrogenolysis to break the C₁-O bond first, followed by dehydration reaction at the Lewis acid sites, thus favoring the production of deeply deoxygenated products (DDPs). A moderate amount of water promoted proton transfer in the HDO process, and adding 8 mg of water increased the DA yield to 66.1 %. The as-prepared catalyst demonstrated acceptable stability during recycling, maintaining a DA yield of 46.64 % after four cycles. Non-metallic phosphorus doping provides a viable strategy for modifying the electronic structure and acid-site properties of catalysts, enabling the selective retention of oxygen-containing functional groups in biomass condensation intermediates.