Construction Of Bifunctional Catalysts And Their Synergistic Catalytic Hydrodeoxygenation Performance

The replacement of fossil resources by lignin aromatic polymers and their depolymerization products,bio-oils,to produce biofuels or high-value chemicals is the most promising pathway to achieve sustainable development.Hydrodeoxygenation（HDO）is the main technology for the catalytic conversion of bio-oils with high oxygen content into liquid hydrocarbon fuels.However,bio-oils with a mixture of oxygen-containing groups usually require multi-step HDO processes to remove oxygen-containing groups with different chemical stability to meet the standards of transportation fuels.Highly chemically reactive oxygen-containing compounds（such as alcohols,aldehydes,ketones,etc.）are typically hydrotreated at low temperatures to reduce the formation of condensation products or carbon deposits.In contrast,chemically stable phenolic compounds（4-O-5,β-O-4,α-O-4,etc.）are often deeply deoxygenated at high temperatures under harsh conditions（200～500°C,2～20 MPa H₂）to obtain high-octane fuels.HDO involves a series of reactions such as hydrogenation,hydrogenolysis,dehydration and decarbonylation,while catalyst with single active site is often difficult to meet the multi-step cascade reactions catalyzed by different sites.Therefore,it is a great challenge to design a catalytic system with multiple（dual）active site types（usually metal and acid sites）for efficient deoxygenation of bio-oils under different hydrotreating conditions.Among them,the effective synergy between the hydrogenation activity on metal sites and the deoxygenation performance on acid sites is the key for fast and selective upgrading of bio-oils.Additionally,a small amount of alkali and alkaline earth metals carried by the bio-oils itself are deposited on the catalyst surface or enter the pores during the reaction,poisoning the active sites and causing irreversible deactivation of catalyst.Therefore,the development of efficient and alkali metal-resistant catalyst is the crux of the industrial production of value-added products from bio-oils instead of fossil resources.To address the above problems,this paper designs bifunctional catalytic systems applicable to different types of HDO reactions,and in-depth investigates the mechanism of the improvement of activity and selectivity by two sites,which provides a new strategy for the design and development of high-performance alkali-resistant catalysts.In the second chapter of this paper,the Pd catalyst（Pd/HPC-NH₂）supported on-NH₂ modified hierarchical porous carbon material（HPC）with formic acid（FA）as a hydrogen source,achieves efficient selective upgrading of benzyl ketones from lignin-derived mixed oxygen-containing monomers under mild conditions.Designed experiments and theoretical calculations（DFT）show that the H⁺/H^-species generated from FA decomposition at Pd and-NH₂ dual sites accelerates the hydrogenation of polar C=O bonds in benzyl ketones,and the formation of benzyl formate by esterification of intermediate alcohols with FA accelerates the breakage of C-O bonds through a thermodynamically favorable esterification-decarboxylative deoxygenation（EDDO）pathway.The effective synergy of these two processes achieves a rapid HDO of vanillin at 30°C.This work provides a green pathway to produce transportation fuels or high-value chemicals from biomass only under mild conditions.In the third chapter of this paper,Pt Fe₅/WO_x and Pt/WO_x mixed relay catalyst is developed by doping oxophilic Fe to modulate the adsorption strength of oxygen-containing compounds and the concentration of Br（?）nsted acid sites（BAS）.In this novel relay catalytic system,the introduction of Fe O_x species in Pt Fe₅/WO_x promotes the adsorption of oxygen-containing compounds,thereby increasing the hydrogenation rate of m-cresol and 3-methylcyclohexanone（MCHone）.While Pt/WO_x with more BAS facilitates the breakage of C_alkyl-O bonds in 3-methylcyclohexanol（MCHol）,and thus exhibits excellent deoxygenation activity.By balancing the hydrogenation and dehydration performance,the relay catalytic system achieves higher activity than a single catalyst in the HDO of m-cresol with a turnover of frequency（TOF）up to 671.5h^-1.This finding provides a new idea for the design of catalysts for complex reactions with multiple elementary steps.In the fourth chapter of this paper,a series of Pt K/WO_x-IM catalysts are designed to investigate the poisoning effect of K on the acid sites and Pt sites of WO_x surface by exploiting the reducibility properties of acidic WO_x.By changing the impregnation sequence of the catalyst or adjusting the particle size of Pt particles,the poisoning of K on Pt active center can be effectively inhibited;The hydrogen spillover between Pt and WO_x and the heterolytic cleavage of H₂ by defective WO_x under reaction conditions can in-situ generate new acid sites,reducing or counteracting the effect of K on the poisoning of surface acid sites.Moreover,the introduction of K promotes the desorption of H₂ and strongly adsorbed olefins on the surface of catalyst,which is beneficial to the hydrogenation of the olefin intermediates.Thus,the 0.2Pt0.8K/WO_x-IM catalyst with highly dispersed Pt has the highest HDO activity with a MCHol reaction rate up to 261m L·g_cat.^-1·h^-1,which is 3.6 times higher than that of undoped K catalyst.This K-promoting effect is expected to be extended to WO_x and other acidic reducible oxide supported metal catalysts,opening up a new pathway for the design of efficient anti-K poisoning catalyst.