Synthesis Of Dawson-type Polyoxometalates And Their Properties In Catalyzing The Hydrothermal Conversion Of Cellulose

Bio-or chemical conversion of biomass can produce a variety of platform compounds,and some products with great commercial benefits can be obtained.Among them,the catalytic conversion of cellulose in aqueous phase is a promising method for obtaining high-value products.Therefore,with water as the reaction medium and cellulose as the substrate,this paper is devoted to finding a suitable heterogeneous solid catalyst to replace the enzyme or the traditional homogeneous acid catalyst to achieve the targeted conversion of cellulose.Polyoxometalates?POMs?have both acid and oxidizing power,and can be cured by changing their composition,immobilization,etc.So the state of the catalytic reaction and the composition of the active component are changed to obtain a composite catalyst having high catalytic activity.Most of the POMs that have been concerned in the past have focused on the catalytic activity of Keggin-type polyoxometalates,while the Dawson structure has little research.Therefore,Dawson structure polyoxometalate H₆P₂Mo₁₈O₆₂ was selected as the research object,and two heterogeneous multi-functional POMs catalysts were designed and synthesized by introducing cation and immobilization strategies,and applied to catalyze the hydrothermal generation of cellulose.The specific work is as follows:1.Dawson-type H₆P₂Mo₁₈O₆₂ was selected as a catalyst to catalyze the hydrothermal conversion of cellulose,and its mechanism was characterized by infrared,solid ultraviolet,XRD,et al.Catalytic activity of H₆P₂Mo₁₈O₆₂ was investigated by catalyzing the hydrothermal conversion of cellulose as a model reaction.The optimal catalytic conditions were:0.1 g of cellulose,0.05 g of H₆P₂Mo₁₈O₆₂,7 mL of deionized water,160 ^oC,10 h.The conversion of cellulose under this condition was 94%,and the yields of lactic acid and formic acid were 48.2%and 20.2%,respectively.The results show that H₆P₂Mo₁₈O₆₂ exhibits good catalytic performance due to its strong acidity and strong oxidizability.Moreover,the catalyst recovered by the extraction of diethyl ether showed that the structure did not change before and after the reaction of the catalyst,therefore its stability was good.2.the Dawson-type Ag_xH_6-xP₂Mo₁₈O₆₂?x=1,2,3,4,5,6?was synthesized and characterized by IR,solid ultraviolet,XRD,et al.Catalytic activity of Ag_xH_6-xP₂Mo₁₈O₆₂?x=1,2,3,4,5,6?was investigated by catalyzing the hydrothermal conversion of cellulose as a model reaction.When the cellulose is 0.1 g,the optimal catalytic conditions are as follows:0.08 g Ag₂H₄P₂Mo₁₈O₆₂,7 mL deionized water,150 ^oC,13 h.The conversion of cellulose under this condition was 100%,the yields of lactic acid and formic acid were 57.8%and13.6%,respectively.After the regulation of the acidity of B acid and L acid,it was found that the catalytic activity of Ag₂H₄P₂Mo₁₈O₆₂ was significantly better than that of H₆P₂Mo₁₈O₆₂.It was proved that the introduction of Lewis acid sites?L acid?into Br?nsted acid?B acid?H₆P₂Mo₁₈O₆₂ can improve the catalytic activity of POMs in the hydrothermal conversion of cellulose.At the same time,the homogeneous H₆P₂Mo₁₈O₆₂ was converted into a heterogeneous catalyst by the solidification method of the protons in the inorganic cation exchange H₆P₂Mo₁₈O₆₂.The stability was better,and the catalytic activity was not significantly reduced after five cycles of recycling.3.Heterogeneous acid-base dual-center P₂Mo₁₈/PANI catalyst was synthesized by H₆P₂Mo₁₈O₆₂ doped polyaniline?PANI?,and characterized by IR,solid ultraviolet,XRD,et al.Catalytic activity of P₂Mo₁₈/PANI catalyst was investigated by catalyzing the hydrothermal conversion of cellulose as a model reaction.The optimal reaction conditions were as follows:when the cellulose was 0.1 g,0.2 g of P₂Mo₁₈/PANI?30%?catalyst,7 mL of deionized water,160°C,8 h.The conversion of cellulose under this condition was 74%,and the yields of lactic acid and formic acid were 30.9%and 2.8%,respectively.Studies have shown that the basicity of the catalyst is favorable for the formation of lactic acid.The solid catalyst showed good stability and its catalytic performance was not significantly reduced after five cycles of recycling.