Hydrodeoxygenation Of Lignocellulose-based Oxygenates Catalyzed By Metal Phosphide/phosphate Catalysts

Fossil resources bring many conveniences to human beings,but the excessive reliance on non-renewable fossil resources for the production of chemicals and fuels has also led to a series of environmental problems such as air pollution and global warming.Therefore,developing renewable resources that are both economically viable and environmentally friendly to replace fossil resources is of great significance.Lignocellulose biomass is abundant,renewable,and inexpensive.A series of oxygencontaining derivatives such as guaiacol,vanillin,furfural,and levulinic acid can be obtained from lignocellulose,which can be further transformed into various high-value chemicals and fuels through selective hydrodeoxygenation.Currently,most hydrodeoxygenation catalysts are based on expensive and scarce noble metal catalysts with high catalytic efficiency,which is not conducive to industrial applications.Low costly non-noble metal catalysts require harsh reaction conditions and are prone to deactivation,and their activity and stability need to be further improved.To address these issues,we have developed non-noble metal phosphide/phosphate catalysts for the hydrodeoxygenation of lignocellulose-based oxygenates into chemicals or fuels.In the first study,in order to improve the stability of non-noble metal catalysts in hydrodeoxygenation reactions,we prepared a series of encapsulated cobalt phosphide/manganese phosphate catalysts Co2P@MnP-x(x=1-5)and used them under harsh and easily leachable acidic conditions to catalyze the reaction of levulinic acid to y-valerolactone.Here,x represents the molar ratio of the P precursor and Mn precursor in the support synthesis process.Under mild conditions of 100℃ and 3 MPa H2,the encapsulated Co2P@MnP-3 catalyst obtained y-valerolactone yield of 97.4%,and the catalyst maintained high catalytic activity even after repeated use five times,significantly improving the acid resistance of non-noble metals.Characterization revealed that the high activity of the Co2P@MnP-3 catalyst was mainly attributed to the excellent hydrogenation activity of encapsulated Co2P sites.An appropriate P:Mn ratio promotes the interaction between the metal and the support.The encapsulated structure endowed the catalyst with high stability under acidic conditions.Although the encapsulated Co2P@MnP-3 catalyst can improve stability,the catalytic activity for deep hydrodeoxygenation is limited due to the constraints imposed by the properties of Co and encapsulated structure.Nickel has good hydrodeoxygenation activity.In the second study,we prepared different phosphorization levels of Ni-based/cerium phosphate catalysts by in-situ phosphorization and adjusting the metal-support interaction,and used them to catalyze the selective hydrodeoxygenation of lignin-derived phenolic compounds.Among them,the Ni3P/CeP-3 catalyst with suitable metal-support interaction can catalyze the conversion of vanillin into three different value-added chemicals under mild reaction conditions.It can obtain 2-methoxy-4-methylphenol at 90℃ and 1 MPa H2,4methylcyclohexanol at 200℃ and 1 MPa H2,and methylcyclohexane at 240℃ and 3 MPa H2.It also has good hydrodeoxygenation performance for other lignin-derived phenolic compounds.A series of characterizations revealed that the metal-support interaction enabled Ni3P/CeP-3 to provide smaller Ni3P particle size and more positively charged Niδ+ active sites,enhancing the ability to adsorb and activate oxygencontaining compounds.DFT calculations and in-situ FTIR experiments demonstrated that Ni3P/CeP-3 removed methoxy group through tilted adsorption model,promoting the selective hydrodeoxygenation performance of the methoxy group.