Fine Regulation Of Catalysts With Dual Active Sites And Their Performance Towards Catalytic Transfer Hydrogenation Of Furfural

Furfural,as an important C₅ platform molecule with multiple structural groups（carbonyl,alkenyl,ether bonds）,can be further upgraded to furfuryl alcohol,2-methylfuran and other high value-added chemicals through hydrogenation.Compared with the traditional hydrogenation using H₂,the catalytic transfer hydrogenation using hydrogen-containing chemicals（especially abundant and inexpensive alcohol compounds）as hydrogen donors,is a green,safe,and economical alternative method,which avoids the use of high-pressure hydrogen and greatly reduces the cost of reaction equipment.Researchers have found that catalysts with dual active sites（acid-base catalysts and metal catalysts）exhibit good catalytic performance towards catalytic transfer hydrogenation reactions,and appropriate combination of catalyst and hydrogen donor can also improve the reaction performance（conversion,selectivity,reaction rate,etc.）.However,some problems and challenges still remain unresolved.Most catalysts have limited activity and exhibit low reaction rates.The structure of dual active sites is complex and the preparation process is cumbersome,making it difficult to finely control the catalyst microstructure.The catalytic reaction pathways and reaction mechanisms,especially the synergistic effect of active sites and their role in the transfer of active hydrogen species are not fully understood,which hinders the further optimization of catalyst structure and performance.In this dissertation,three kinds of dual active sites catalysts（acid-base catalysts,metal catalysts and metal-acid catalysts）were prepared based on composition tunability and structural topological transformation of layered double hydroxides（LDHs）precursors.The resulting catalysts exhibited high-performance for catalytic transfer hydrogenation of furfural by using isopropanol as hydrogen donor.In addition,a comprehensive investigation including experimental studies and theoretical calculations was carried out to study the structure-property correlation and the synergetic effect of dual active sites.The transfer path of active hydrogen species as well as catalytic reaction mechanism were systematically revealed.This dissertation provides rational design,preparation and optimization of high-performance catalysts with dual active sites,which can be potentially used in catalytic transfer hydrogenation reactions.The main research contents are as follows:1.Regulation of acid-base catalysts and studies on reaction mechanism in catalytic transfer hydrogenation of furfuralA Co-Al mixed metal oxide catalyst（Co₁Al₂-MMO-T,T=calcination temperature）with tunable acid-base sites was obtained by fine control of calcination temperature of Co₁Al₂-LDHs precursor,which was used in furfural catalytic transfer hydrogenation using isopropanol as hydrogen donor.The optimal catalyst（Co₁Al₂-MMO-200）shows a furfural conversion of 97.4%and furfuryl alcohol selectivity of 97.2%under mild conditions（150°C,1 MPa N₂）,and the reaction rate reaches up to 0.023 mol g^-1 h^-1,which is superior to previously reported acid-base catalysts.A joint study of NH₃-TPD,CO₂-TPD,and poisoning experiment confirms that the synergetic effect of acid-base sites plays a crucial role in this catalytic system.Experiment investigations（isotopic labelling MS,in situ FT-IR）and DFT studies further reveal the catalytic transfer hydrogenation of furfural over the acid-base sites occurs through the Meerwein-Ponndorf-Verley（MPV）route:the base site promotes the deprotonation of isopropanol,while the acid site facilitates the formation of a six-membered ring transition state.This work proves the synergistic catalysis of acid-base sites derived from LDHs,which shows potential applications in catalytic transfer hydrogenation reactions.2.Regulation of Cu-based catalysts and studies on reaction mechanism in catalytic transfer hydrogenation of furfuralA Cu-based catalyst（Cu/Cu Al-MMO）supported on Cu Al-mixed metal oxide was prepared by structural topological transformation of Cu₂Al-layered double hydroxides（Cu₂Al-LDHs）precursor,which displayed good catalytic behavior towards furfural catalytic transfer hydrogenation using isopropanol as hydrogen donor（conversion:98.0%;furfuryl alcohol selectivity:97.9%）.Notably,the reaction rate of the optimal catalyst（Cu/Cu Al-MMO-400）reaches up to 0.125 mol g^-1 h^-1,which is significantly better than previously reported non-precious metal catalysts.The qualitative and quantitative analysis based on a combination investigation including N₂O titration,XPS and XAES confirms that the Cu⁰/Cu⁺molar ratio on the catalyst surface can be finely regulated by adjusting the reduction temperature.Both experiment investigations（isotopic labelling MS,in situ FT-IR）and DFT studies verify that Cu⁰ site and Cu⁺site play a crucial role in the catalytic transfer hydrogenation of furfural through the metal hydride pathway:the Cu⁺site facilitates the activation adsorption of isopropanol and furfural;while the Cu⁰ site boosts the transfer of active hydrogen species between adsorbed substrates.This work reveals the Cu⁰-Cu⁺synergistic effect by establishing the structure-property correlation,which provides a way for rational design and preparation of efficient metal catalysts for catalytic transfer hydrogenation.3.Regulation of Pd-acid catalysts and their catalytic performance in catalytic transfer hydrogenolysis of furfuralA Pd-based catalyst（0.8%Pd/Co₂Al-MMO-T,T=reduction temperature）supported on Co Al-mixed metal oxide was prepared by a two-step method including calcination of Co₂Al-LDHs followed by impregnation treatment.The fine regulation of the acid site and Pd site were realized by tuning the calcination temperature and reduction temperature,achieving the performance optimization of the catalytic transfer hydrogenolysis reaction of furfural to 2-methylfuran with isopropanol as the hydrogen donor.The optimal catalyst（0.8%Pd/Co₂Al-MMO-250）shows a furfural conversion of 100%and 2-methylfuran selectivity of 88.9%at 2.5 h.The formation rate of 2-methylfuran reaches 0.026 mol_2-MFg^-1 h^-1,which exceeds the previously reported noble metal catalysts.A combination investigation base on NH₃-TPD,XPS and XANES provides detailed information of the acid site on the catalyst surface and the electronic and coordination structures of Pd.Combined with the evaluation results of catalytic performance,the structure-property correlation was established to reveal that the synergetic effect of Pd^δ-site and acid site plays a crucial role in the catalytic transfer hydrogenolysis reaction.This work provides a facile preparation method for metal-acid catalysts,which has potential application prospects in catalytic transfer hydrogenolysis reactions.