Pt-loaded Nb-W Composite Oxide For Selective Cleavage Of Secondary C-O Bonds In Biomass Polyols

In order to pursue the vision of sustainable development,the lowcarbon and green transformation of global energy will become an important way to coordinate the common development of energy,environment and economy.Biomass resources,the main form of renewable energy utilization,can be directionally converted into fuel additives or high value-added chemicals under the catalysis of high efficiency catalysts.Still,majority biomass molecules contain a higher oxygen content,requiring an additional reduction step to convert them into value-added chemicals.Unfortunately,the effective removal of C-O bonds,especially secondary C-O bonds,is challenging,which limited by steric hindrance and thermodynamic factors.Therefore,the precise control of C-O bond activation is instrumental for biomass valorization and fine chemical industry.Glycerol hydrogenolysis to 1,3-propanediol(1,3-PDO)is considered to be one of the most promising reactions in biomass valorization.The precise activation mechanism of secondary C-O bond involved in this reaction provides insights and feasible solutions for other biomass molecules hydrogenolysis.To this aim,this work designed and prepared a series of Pt-supported Nb-W complex oxides for glycerol hydrogenolysis.The synergistic relationship between Pt and Nb-W composite oxide on secondary C-O bond activation was investigated.In addition,a comprehensive in situ characterization was used to trace the activity mechanism of the catalyst,while the structure-performance relationship was established.On this basis,the catalyst was further extended to the selective hydrogenolysis of other heterocyclic molecules.The main research content is divided into the following aspects:(1)Precise activation of C-O bonds of glycerol molecule is the key step to realize the high yield of catalytic conversion.Here,a Pt-loaded Nb-W composite oxides with crystallographic shear phase for the precise activation and cleavage of secondary C-O bonds are first reported.The developed Nb14W3O44 with uniform structure possesses arrays of W-O-Nb active sites that totally distinct from individual WOX or NbOX species,which is superior to the adsorption and activation of secondary C-O bonds.The Nb14W3O44 support with rich reversible redox couples also promotes the electron feedback ability of Pt and enhances its interaction with Pt nanoparticles,resulting in high activity for H2 dissociation and hydrogenation.All these favorable factors confer the Pt/Nb14W3O44 excellent performance for selective hydrogenolysis of glycerol to 1,3-PDO with the yield of 75.2%,paying the way for the commercial development of biomass conversion.(2)To achieve the efficient conversion,the selective activation of the secondary C-O bonds in the glycerol is vital.In this work,we comparatively investigated the catalytic performances of glycerol hydrogenolysis on Pt/Nb2W3O14 catalyst controlled at the reacting conditions of 140℃and 40 bar.Compared to Pt/WO3 and Pt/NbOx,the space-time yield of 1,3-PDO over Pt/Nb2W3O14 catalyst can be improved by a factor of 13,reaching 596.4 mg gcat"1 h-1.The cation ordering of Nb and W on atomic-scale were fully synergized their unique advantages,showing preferential adsorption of the secondary C-O bond under in-situ DRIFTS tracking.The prepared Nb2W3O14 is a tetragonal tungsten bronze(TTB)type complex oxides which can effectively promote the dispersion and reduction of Pt nanoparticles.Such strong interaction between Nb2W3O14 and Pt can coordinate the precise adsorption and activation of the secondary C-O bond,simultaneously triggering subsequent hydrogenation.Nb2W3O14 affords an ultrahigh activity in glycerol hydrogenolysis to produce 1,3-PDO.(3)The selective hydrogenolysis of glycerol to 1,3-PDO necessitates the precise tandem of deoxygenation at a specific location and ensuing hydrogenation steps.Here,a solid solution-supported catalyst Pt/Nb2W15O50 was reported for the hydrogenolysis of glycerol to 1,3-PDO.We engineered the exceptional interaction between active Pt and oxygen vacancies to efficiently integrate the deoxygenation and hydrogenation steps in tandem.The strong interaction between active Pt and oxygen vacancies was established via hydrogen spillover and induced the generation of 1,3-PDO in situ.This synergistic effect confers the Pt/Nb2W15O50 with an excellent catalytic performance,combining a 75.6%conversion of glycerol and 66.5%selectivity to 1,3-PDO at a low H2 pressure of 1.0 MPa(noting that most catalysts require H2 pressures of≥ 4 MPa).Moreover,the structure-performance relationship validated that there is a linear correlation between active Pt,oxygen vacancies and 1,3-PDO yield.(4)The upgrading of heterocyclic molecules such as tetrahydrofurfuryl alcohol via ring-opening is a promising pathway to produce value-added diol of 1,5-PeD.The Co or Pt supported NbW composite metal oxides were prepared and applied to the selective hydrogenolysis of tetrahydrofurfuryl alcohol.Raman and HRTEM result demonstrated that the introduction of Co will destroy the structure of NbW support,Moreover,Co was easy to agglomerate on the support,and it is difficult to establish an effective synergistic effect between them.In contrast,the strong interaction between Pt and NbW can improve the activation selectivity of secondary C-O bonds.At 90℃and 8 MPa,Pt/NbW catalyst offered 91.0%yield of 1,5-pentanediol in hydrogenolysis of tetrahydrofurfuryl alcohol.