Catalytic Activity Of Multi-active-centers POMs In Glycerol Cascade Conversion

With the world's energy crisis and environmental problems becoming increasingly serious,searching for new alternative energy sources has become an inevitable choice for modern society.So biodiesel emerged as a new alternative to fossil energy.The mass production of biodiesel is inevitably accompanied by a large accumulation of glycerol,a major by-product.The price of glycerol keeps decreasing even to zero because of its purify problem.In recent years,scientists have designed dozens of methods for converting glycerol,among which,glycerol oxidation to high valuable chemicals attracts much attention.The most popular methed is production of lactic acid?LA?through glycerol cascade reaction including dehydrogenation,dehydration and hydration catalyzed by noble metals under base condition.This process leads to some problems such as high catalysts price,complex subsequent treatment of basic system.It is an urgent problem to desigh an earth-abendent and base-free system to produce LA.Polyoxometalates?POMs?are common in acid or redox catalysis reactions.There are only a few reports on POMs catalyzing organic cascade reactions.To investigate the influence of POMs'composition and structure on glycerol cascade reaction is very useful in designing multi-active-centers POMs synstem.So we did the following investigations:1.A series of POMs with different centra atoms and coordibation atoms(H₅PMo₁₀V₂O₄₀,H₃PMo₁₂O₄₀,H₃PW₁₂O₄₀,H₄SiMo₁₂O₄₀,H₄SiW₁₂O₄₀)and counter cations(MPMo₁₂O₄₀,M=Al³⁺,Cr³⁺,Fe³⁺,Cu²⁺,Zn²⁺)were synthesised and applied in glycerol cascade oxidation.The machenism of activing molecular oxygen was also studied through quenching and initiation reaction.We have found that POMs with Mo and P shown excellent activity in glycerol cascade reaction.Al³⁺as a suitable Lewis metal ion was chosen to be a counter cation in POMs,which could active molecular oxygen to produce free radicals.2.A serious of heterogeneous POM catalysts MPMo₁₂O₄₀(M=Ti⁴⁺,Al³⁺,Fe³⁺,Cr³⁺,Zr⁴⁺and Zn²⁺,abbreviated as MPMo)were synthesized through ion exchange and calcination dehydration.The influence of Lewis acid metal as counter cation on the total acidity and redox properties of POMs was studied.The materials were also applied in glycerol cascade reaction to understead the effect of Lewis acid on every step during the whole process.the stability and recyclability were also studied in the pepeating experiments.3.A serious of heterogeneous POM catalysts H_xPMo₁₁MO₄₀(M=Ti⁴⁺,Al³⁺,Sn⁴⁺,Fe³⁺,Cr³⁺and Zn²⁺;for Ti⁴⁺and Sn⁴⁺,the amount of oxygen atom is 40)were synthesized through substitution reaction and calcination dehydration.The influence of Lewis acid metals as substituded atoms on the total acidity and redox properties of POMs was studied.The materials were also applied in glycerol cascade reaction to understead the effect of Lewis acid on every step during the whole process.the stability and recyclability were also studied in the pepeating experiments.4.According to the research of?2?,the variety of Lewis acid metals not only affects the total acidity and redox property of POMs,but also plays an important role in glycerol cascade reaction.Ag⁺is a common counter cation of POMs with the reaction of Ag⁺+e^-+H₂O?Ag+H⁺.The combiding of Ag⁺as a special Lewis metal ion and HPMo would affect the chemical and physical properties of POMs.Based on the above opinions,a series of silver-exchanged phosphomolybdic acid catalysts Ag_xPMo₁₂O₄₀?x=1,2,3?was prepared.It was found that Lewis metal Ag⁺and its amount could enhance the redox potentials and acidity of H₃PMo₁₂O₄₀.The materials were also applied in glycerol cascade reaction to understead the effect of Lewis acid in every step during the whole process.The stability and recyclability were also studied in the pepeating experiments.5.A series of amino acid/POMs compound catalysts Ly_xH_3-xPMo₁₂O₄₀(n=1,2,3,abbrived as Ly_xH_3-xPMo,Ly=C₆H₁₅O₂N₂)with triple active sites was fabricated,and their catalytic activities in glycerol oxidation were investigated under mild reaction conditions.The compose,structure and shape of POMs were studied.The relationship between their structure and activity,and the mechenism of glycerol cascade reaction was studied in detail.such hybrids also showed long duriation and stability.6.H3PMo12O40/Carbon?HPMo/C?was prepared using natural catkin as carbon support,by chemical modification.Characterized its compose and structure and investigated its catalytic activity in glycerol oxidation.Through glycerol cascade reaction,we found carbon support could approve the POMs catalytic activity,and the covalent immobilization could cooperate with POMs.Using recycling experiments confirmed the stability,no leaching and high reusability of the catalysts,which also confirmed that carbon is a good support of POMs.7.A new strategy for immobilization of POMs on graphene oxide?GO?has been developed to form HPMo@lipid?n?/GO hybrid materials and characterized their compose and structure using a series of technology.The catalytic activity of HPMo@lipid?n?/GO was inspected in glycerol cascade reaction.Apart from the benefits of resistance of HPMo against leaching and good stability towards pH and temperature changes,such HPMo@lipid?n?/GO provides capillary-like assembly with hydrophobicity during catalytic reactions.Furthermore,the oxidative ability of HPMo can be enhanced by GO support and tuned by changing the length of alkyl chain in the lipid bilayer.