Design And Mechanism Of Wood Cellulose-Based High-Performance Catalytic Materials

The efficient conversion and functionalized utilization of forestry wastes has been the important research contents.As the most abundant in the wood resources,cellulose has many advantages such as regular molecular structure,abundant surface functional groups with multi-scale structure.Therefore,the development cellulose-based catalytic materials with such abundant,low-cost and mass-producible,then the study of their structure-activity relationship and functional applications,are important elements of this dissertation.In this thesis,naturally abundant and renewable wood fibers used as raw materials and modulated it at the multi-level scale to achieve the preparation of high-performance catalytic materials.Esterified CNF were isolated and prepared from wood fibers,and CNF-Pd catalytic material with high loading of palladium nanoparticles（Pd NPs）was prepared by the double confinement combining the chemically confined and spatial confined of self-assembled nanoporous structures.Starting from cellulose molecular scale anchored heteroatom precursors,the nanoporous carbon catalytic materials with high content of phosphorus doped,boron-phosphorus co-doped and sulfur-phosphorus co-doped were prepared with supramolecular collosol doping/co-doping carbonization strategy.Density functional calculations（DFT）help us to clearly explore the active sites and the catalytic mechanisms.The influence of the electronic structures of the co-doped atoms and the synergies on the carbon matrix were investigated.The main research contents and results are as following:（1）In the first work,functionalized CNF were prepared by modifying the surface groups of cellulose using hydrated deep eutectic solvent.CNF-Pd catalyst with dual synergistic confinement effect was designed by using the self-assembling of hydrogen bonds between hydroxyl groups on their nano-skeleton.Activity for hydrogenation of 4-nitrophenol and catalytic selectivity of functionalized nitroanilines were investigated.Results show that the as-prepared CNF-Pd possesses uniformly distributed and highly exposed Pd NPs（6.2 nm,loading up to 9.6 wt%）to ensure the excellent catalytic reactivity.It is resulted from the spatial confinement of carboxyl functional groups on the surface and mesopores structure,making Pd NPs stably dispersed on the matrix of CNF.The CNF-Pd exhibits high catalytic activity for catalyzing hydrogenation of model chemicals at room temperature.The reaction rate constant was calculated to be 8.8×10^-3 s^-1,and the turnover frequency（TOF）reached 2640 h^-1.The combinations of CNF-Pd with suitable solvents exhibit outstanding selective hydrogenation,which was superior to most related catalytic materials reported in the literature.（2）Aiming to the highly effective doping of heteroatoms at molecular scale of cellulose,a collosol-doping carbonization strategy was proposed to prepare P-doped nanoporous carbon（PC）with high P content.The dissolution-doping strategy can fully graft phosphate anions onto the macromolecular chains of cellulose to form supramolecular collosol precursors at room temperature.After directly carbonizing of the collosol,P-doped carbon catalyst with a high specific surface area of 1491 m²/g and high P content of 8.8 wt%was obtained.The doping amount was obviously superior to most P-doped carbon materials prepared by the conventional impregnation method.Due to the high loaded and well-dispersed P atom in the PC,it exhibited excellent catalytic oxidation of benzyl alcohol with high TOF value,low activation energy（Ea）and good cycling stability,which are superior to most reported heteroatom-doped metal-free carbon catalysts and some noble metal-based catalysts.The combination of high P doping,large specific surface area,and abundant lattice defects guarantee the wonderful catalytic performance of the as-developed catalyst,which enhanced the electron transfer ability and helped to improve the adsorption and activation of the reactants.（3）Electron regulation of co-doping of heteroatoms with different electronegativity could lead to optimized catalytic activities of carbon materials.Combined with DFT calculation and experimental verification,we have deeply studied the electron effect on the structure-activity relationship when secondary heteroatoms with different electronegativity were introduced into the active center of co-doped carbon materials.We prepared boron,phosphorus co-doped nanoporous carbon（BPC）with cellulose supramolecular co-doping collosol carbonization method as developed in the previous chapter.The results showed that BPC has better catalytic performance for alcohol oxidation than that of the single P-doped material,attributing to that the rearrangement of electron density of catalytic active center and its surrounding atoms,as well as the change of band gap and new co-active site by the introducing of the lower electronegativity of B atom.Therefore,the BPC enables an entirely different but kinetically and thermodynamically more favorable catalytic reaction pathway.（4）Based on the edge-activated heteroatom co-doping and electronic regulation strategy,unsaturated sulfur atoms were introduced into PC to prepare edge-defect activated co-doped porous carbon（SPC）with tunable catalytic intrinsic activity.The physicochemical properties,the electronic structure,and the oxidation performance of the co-doped SPC were systematically studied.The results show that SPC has rich porous structure and large specific surface area,with uniformly dispersed and ideal loading of heteroatoms.SPC exhibited the best catalytic performance for benzyl alcohol oxidation,and the Ea value was as low as only27 KJ/mol.Moreover,SPC revealed efficient and selective oxidation of primary alcohols with different functional groups to aldehydes with high yields and high selectivity,higher than 95%within 1 h.It also proved that the Fermi level of the unsaturated edge S atom had a higher density of state,ensuring more conducive to electron transfer.The synergistic catalytic effect of co-doping with high P content and edge S active sites further enhanced the overall activity of the catalyst.