Study On The Properties Of Molybdenum-Containing Polyoxometalates In Cellulose Conversion

With the excessive consumption of fossil fuels and the deterioration of environmental problems,the existing crisis has led to an increasing demand for biomass energy.Biomass feedstocks are taking the place of petroleum and the conversion of biomass feedstocks into fine chemicals is considered a very significant challenge.Cellulose is a rich natural carbon material that has been favored for its renewability and degradability and it is considered a potential resource for the production of bioplatform chemicals in place of fossil fuels.The lactic acid and formic acid produced in the process of cellulose conversion are two important organic acids,and their roles in various fields cannot be ignored.Therefore,Using one-step method to convert cellulose further into a small practical acid of high practical value is invaluable.Polyoxometalates have strong Br?nsted acidity and strong redox properties,and the study of Polyoxometalates has been an important field of research in biomass conversion as a highly efficient and highly selective catalyst application.Based on this,this paper uses H₃PMo₁₂O₄₀?HPMo?with Br?nsted acid and redox ability as the research object and introduces sulfonic acid organic counter cation,Lewis acid Ag⁺,synthetic ionic liquid type catalyst[C₄H₆N₂?CH₂?₃SO₃H]_xH_3-xPMo₁₂O₄₀(abbreviated as[MIMPS]_xH_3-xPMo)?x=1,2,3?and Ag-substituted Ag_xH_3-xPMo₁₂O₄₀(abbreviated as Ag_xH_3-xPMo)?x=1,2,3?,and investigated its activity in cellulose catalytic oxidation experiments,the specific research contents are as follows:1.Keggin-type HPMo heteropoly acid was used for characterization of solid ultraviolet,IR,CV,³¹P NMR and XRD.It was applied to the catalytic oxidation of cellulose to explore the optimal conditions:6.0 mL water consumption,catalyst 0.06 mmol,1.0 MPa of oxygen was introduced at 150°C,and the reaction was carried out for 8 h.The conversion of cellulose reached 87.4%,the yield of lactic acid was 52.2%,the selectivity of lactic acid was59.7%,the yield of formic acid was 31.9%,and the selectivity of formic acid was 36.8%.The activity of the catalyst in this reaction was found to be mainly derived from Br?nsted acidity and oxidizability.After the reaction,the catalyst was recovered and reused.After repeating the experiment for 5 times,the conversion of cellulose was only reduced by 3.6%,and the structure of the compound remained stable before and after the reaction.2.An organic cation-substituted ionic liquid catalyst[MIMPS]_xH_3-xPMo?x=1,2,3?was designed and synthesized,and characterized by solid ultraviolet,elemental analysis,IR,CV,HPMo proton hydrogen is substituted,the Br?nsted acidity of the polyacid is lowered,the cellulose conversion rate is slightly decreased,but the selectivity to lactic acid is increased.The exploration conditions were as follows:using 6.0 mL of distilled water and 0.06 mmol of catalyst at 150°C,the reaction was carried out for 8 h,and 0.1 g of microcrystalline cellulose was oxidized.It was found that[MIMPS]₁H₂PMo exhibited the best activity,the conversion of cellulose under optimal conditions was 82.0%,the yield of lactic acid was 50.5%,the selectivity of lactic acid was 61.6%,the yield of formic acid was 24.8%,the selectivity of formic acid was 30.2%.The catalyst was recycled for 5 times after the reaction,the conversion of cellulose was reduced by 4.2%,the yield of lactic acid was decreased by 3.2%,and the structure of the recovered catalyst was kept stable.3.Lewis metal Ag⁺was introduced into strong Br?nsted acidic HPMo to synthesize Ag_xH_3-xPMo?x=1,2,3?,and the polyacid silver salt was characterized by elemental analysis,solid ultraviolet,IR,SEM,XRD,³¹P NMR,CV,etc.Determination of Br?nsted acid and Lewis acid in the catalyst by potentiometric titration and pyridine adsorption infrared,combined with oxidation-reduction potential in cyclic voltammetry,determined the structure-activity relationship of Ag_xH_3-xPMo?x=1,2,3?on cellulose oxidation.In the optimized experimental conditions,it was found that 0.06 mmol of Ag₁H₂PMo,0.1 g of microcrystalline cellulose and 6.0 mL of distilled water were added at 150°C,and 1.0 MPa of oxygen was introduced.After 8 h of reaction,the conversion of cellulose was 66.0%,and the yield of lactic acid was 40.9%.The selectivity was 62.0%,the yield of formic acid was 18.8%,and the selectivity for formic acid was 28.5%.After the heterogeneous Ag₁H₂PMo was used for 5 times in repeated cycles,the cellulose conversion rate decreased by 3.8%and the yield of lactic acid decreased by 2.7%,indicating that the catalyst has good practicability and stability.