Studies On The Preparation Of High Performance Catalysts Towards Hydrodeoxygenation Reaction Of Biomass Platform Molecules

With the excessive exploitation of fossil fuel,renewable and green resources are desirable for the world.In recent years,the conversion of biomass resources into high-energy fuels or high value-added chemicals has become a hot topic in the field of biomass utilization.Hydrodeoxygenation（HDO）of platform compounds is one of effective ways to convert biomass resources into liquid fuels or fine chemicals,and the research and development of efficient catalysts plays a key role.Although considerable progress has been made in this field,the following problems and challenges remain unresolved:structural design and preparation of highly efficient catalysts are difficult task;the selective control over catalytic conversion of biomass platform needs to be improved;the catalytic mechanism for the HDO reaction of biomass platform molecules is still controversial.Therefore,the rational structure design,structure-activity correlation study and catalytic performance enhancement of high performance catalysts are critical issues to be solved in this field.Based on the above key issues,three supported catalysts,namely Ru-O_v/Mg O single atom catalyst,Pt₁/Co₂Al O₄ single atom catalyst and Co-MoO_xcatalyst,were prepared based on a topological transformation process of layered double hydroxide（LDHs）precursors.Efficient HDO reaction of three biomass derivatives（vanillin,5-hydroxymethylfurfural and levulinic acid）with different carbon-oxygen bond were achieved over the above three catalysts,repectively.By virtue of experimental characterizations and theoretical calculations,synergistic catalysis effects in the HDO reaction were systematically studied,and the structure-property relationship between intrinsic active sites and catalytic performance was revealed under in situ conditions.This dissertation provides theoretical insights and practical demonstrations for the rational design and structural optimization of catalysts for HDO reactions of biomass platform molecules,which shows potential applications in biomass upgrading.The main research contents and conclusions of this work are as follows:1.Ru/Mg O single atom catalyst towards HDO reaction of lignin phenolic derivativesBy using LDHs as catalyst precursor,Ru single-atom catalysts supported on Mg O were synthesized through an in-situ incorporation of Ru into Mg Al-LDHs layers followed by a reduction treatment.Among them,the 0.3%Ru/Mg O catalyst achieves a conversion of 99%in HDO reaction of vanillin and a selectivity of 94%towards 4-methylguaiacol;in contrast,the yield of methylcyclohexanol（an aromatic ring hydrogenation product）reaches 92%in the presence of 1.5%Ru/Mg O catalyst.Additionally,the 0.3%Ru/Mg O catalyst exhibits excellent cycling stability and reaction universality.A comprehensive study including STEM,XAFS and in-situ infrared spectroscopy confirms that Ru atoms are distributed in a mono-dispersion state at low loadings of 0.1%and 0.3%.A higher noble metal loading leads to the aggregation of Ru atoms.Combined with in-situ FT-IR and DFT calculations,it is verified that the concentration of Ru-O_v interface sites shows a volcano-shaped variation as a function of Ru loading,with the highest value at 0.3%Ru/Mg O.This unique interface structure facilitates the activation adsorption of aldehyde via a tilt configuration,followed by hydrodeoxygenation process.In contrast,the substrate molecule undergoes adsorption through a flat configuration on Ru NPs,resulting in subsequent hydrogenation of aromatic ring.This work has made valuable explorations in the rational design and structure regulation of single-atom catalysts based on LDHs approach towards HDO reaction.2.Pt₁/Co₂Al O₄ single atom catalyst towards HDO reaction of 5-hydroxymethylfurfuraA series of x%Pt/Co₂Al O₄ catalyst samples were prepared based on topological transformation of hydrotalcite.The 0.4%Pt/Co₂Al O₄ catalyst exhibits excellent catalytic performance in HDO reaction of 5-hydroxymethylfurfural（C=O and C–OH bonds）,with a yield of 99%towards2,5-dimethylfuran（DMF）and a turnover frequency（TOF）of 2553 h-¹.AC-HAADF-STEM,XPS,XAFS and DFT studies confirm the anchoring of Pt single atoms on the Co₂Al O₄ support through bonding with surface oxygen atoms.In-situ FT-IR and XAFS spectroscopy verify that the Pt single atom in the 0.4%Pt/Co₂Al O₄ catalyst facilitates the formation of Co–O（H）–Al（Br（?）nsted acid sites）structure on the surrounding support.The Pt–O and Br（?）nsted acid sites activate the C=O and C–OH bonds in the adsorbed substrate molecule,respectively,thus reducing the adsorption energy barriers.Furthermore,both experimental studies and DFT calculations reveal that the breakage of the first C–OH bond on Pt atomic sites is the rate-determining step;whilst the Br（?）nsted acid sites promote the cleavage of the second C–OH bond.This work provides a successful paradigm of the rational design of single-atom catalysts through LDHs precursor transformation,which can be extended to other biomass catalytic conversion reaction systems.3.Co-MoO_x catalyst towards HDO reaction of levulinic acid intoγ-valerolactoneA series of MoO_x-modified cobalt-based catalyst samples were obtained by introducing Mo elements into Co Al-LDH precursor,followed by an in-situ calcination and reduction treatment.Among them,the Co-MoO_x-500 catalyst shows significant activity in HDO reaction of biomass-derived levulinic acid（C=O and O=C–OH bonds）,with a yield of～99%forγ-valerolactone and a reaction rate of 148.3 mmol LA g_cat^-1 h^-1,which is among the highest level compared with previously reported heterogeneous catalysts.XPS,HR-TEM and in-situ CO FT-IR demonstrate the presence of abundant Co^δ+-Mo⁴⁺bimetal interface sites in Co-MoO_x-500.In-situ FT-IR and DFT calculations reveal that the Co^δ+-Mo⁴⁺bimetal interface sites selectively activate C=O bonds in the levulinic acid molecule with a moderate adsorption strength,thus inhibiting undesired side reactions.At the Co^δ+-Mo⁴⁺interface site,C=O in keto group is prefered relative to C=O in carboxyl group to produce 4-hydroxyvalerolic acid（4-HPA）intermediate,followed by the C–O bond dissociation to obtain the target productγ-valerolactone.This study provides an example of C=O bond activation by tuning the metal-support interface structure,which shows potential applications in biomass HDO upgrading reactions.