Studies On Selective Hydrogenation Of Levulinic Acid Catalyzed By Supported Platinum-Group Metal Nanoparticles

In order to alleviate the increasingly serious environmental pollution and the global energy crisis,researchers began to seek for developing new green and renewable resource utilization schemes.The catalytic hydrogenation of biomass platform compound molecule levulinic acid toγ-valerolactone in liquid-phase is considered to be one of the most promising pathways.However,the reaction pathway is much complex,and hydrogenation and dehydration are contradictory,resulting in much intermediate and by-products.How to harmonize the bifunction of hydrogenation sites and Lewis acid sites for the catalyst is the key scientific problem of the catalytic hydrogenation of levulinic acid toγ-valerolactone.In this paper,we developed Ru/（Al O）（Zr O）_n and Pt/Sn_xMn₁O_y heterogeneous catalysts for the high efficiently catalytic hydrogenation of levulinic acid toγ-valerolactone,by selecting Ru and Pt platinum group metals with excellent hydrogenation performance as hydrogenation sites,and selecting mixed oxides with regulated acid sites as supports.The optimal Ru/（Al O）（Zr O）_0.1 heterogeneous catalyst showed 100%yield toγ-valerolactone in water at 120℃under 1 MPa H₂.PXRD,TEM,XPS,CO chemisorption,CO adsorption DRIFT-IR,NH₃-TPD and pyridine adsorption IR gave insights into the acidic property and surface synergy of the catalysts.Highly active electron-rich Ru~0 sites stabilized by strong metal-support interaction can effectively adsorb and activate molecular H₂ and C=O bond in levulinic acid.Varying Zr/Al ratio and calcination temperature can rationally control the acid strength and acid sites distribution of support.Ru~0 species and Lewis acid sites synergistically enhanced the conversion of levulinic acid and facilitated the intramolecular dehydration of4-hydroxypentanoic acid as intermediate toγ-valerolactone（i.e.,the rate-limiting step）.And this catalyst also presented good stability and reusability.The optimal Pt/Sn_0.8Mn₁O_y heterogeneous catalyst showed 99%yield toγ-valerolactone in dioxane at 120℃under 2 MPa H₂.PXRD,TEM,XPS,CO chemisorption,in situ CO DRIFT-IR,time-resolved DRIFT-IR,H₂-TPR,O₂-TPD and NH₃-TPD were used to investigate the distribution of acid sites,and verify that the C=O group of levulinic acid and molecular H₂ were simultaneously adsorbed,activated and transformed intoγ-valerolactone and water under the surface synergy of deficient Pt sites and the Sn_0.8Mn₁O_y support.The surface reaction mechanism at atomic level on Pt/Sn_xMn₁O_y catalyst was discussed by DFT calculation.The catalyst presented good stability and reusability due to the strong metal-support interaction between Pt~0 and Pt/Sn_0.8Mn₁O_y support.