Synthesis Of Metal Oxide(Ce Or Fe)-Nobel Metal Complex Catalysts For Selectively Catalytic Hydrogenation

Currently,the renewable resources has attracted much attention due to the energy crisis,the pollutants produced by combustion,and increase of cost caused by the shortage of traditional fossil fuels.Biomass is one of the most abundant carbon-containing renewable resources on the earth,which is not only an ideal substitute for conventional fossil fuels,but also as raw materials to transform biomass-derived feedstocks into various types of high value-added chemicals through a variety of physical or chemical methods.Therefore,highly efficient transformation and utilization of biomass has become a new research hotspot.Biomass-based oxygen-containing compounds,especially unsaturated compounds,are important intermediates and platform molecules in the biomass conversion process.Such compounds can be converted to high value-added fine chemicals by various catalytic reactions.Selective catalytic hydrodeoxygenation reduction is one of the most effective methods for conversion of unsaturated oxygen compounds into corresponding value-added products.The realization of these processes is highly dependent on the performance of catalysts.In this thesis,biomass-based unsaturated compounds,such as unsaturated carboxylic acids,aldehydes or ketones,are selected as objective reactants for evaluating the hydrogenation activities of various catalysts.To address some issues existed in current catalytic process,such as the complex catalyst preparation process,poor reusability of catalysts,leaching and agglomeration of active component,and harsh reaction conditions,etc.,we explore a simple,green and efficient synthesis method to fabricate highly active metal/metal oxide complex catalysts for the selective catalytic reduction of biomass-based unsaturated compounds under relatively mild reaction conditions,the main contents and results are summarized as follows:1?Considering that the intrinsic different reduction potential between the metal and the carrier component can spontaneously induce the mutual redox reaction.Therefore,ultilizing the different reduction potential of Pd(?)and Ce(?)precursor to induce the redox reaction,the ceria-palladium complex catalyst(Pd/CeO2)was synthesized in this work.The characterization results demonstrated the average particle size of active metal Pd is about 8 nm and is highly dispersed in CeO2 nanocrystallites.The blocking effect of CeO2 particles can effectively inhibit the aggregation and growth of Pd nanoparticles and thus improve the catalytic activity and of stability Pd particles.Under the mild reaction conditions of 363 K,4 bar H2 and 90 min,the catalyst can absolutely convert levulinic acid into the sole product of y-valerolactone.In addition,the catalyst can be recycled for five successive times without significant deactivation,indicating a good reusability.2??,?-Unsaturated aldehydes are a kind of unsaturated compounds containing conjugated C=C and C=O bonds.Cinnamaldehyde(CAL)is one of the typical representatives of such compounds,and relative studies are very significant.In this work,iron oxide-platinum complex catalysts(Pt/Fe3O4)were prepared by the one-step redox reaction between Pt(IV)and Fe(II)precursor intrigued by their different reduction potential.For the synthesized catalyst,Fe3O4 particles with good electronic modulation ability can effectively increase the surface electron density of Pt particles,which is beneficial to the adsorption of C=O bond on the surface of Pt metal,thus improving the selectivity of cinnamyl alcohol with high productive rate.In addition,the coating and blocking roles of Fe3O4 particles can effectively inhibit the agglomeration of Pt nanoparticles,improving the catalytic activity and stability of Pt.The experimental results showed that the prepared Pt/Fe3O4 catalyst can afford high conversion of 94.2%towards CAL and good selectivity of 92.2%towards cinnamyl alcohol(COL)under the mild reaction conditions of 303 K,5 bar H2 for 150 min.Moreover,the intrinsic magnetism of Fe3O4 nanospheres endows the catalyst with a rapid separation property,favorable for the cycle use of catalyst.3?Pt/Fe3O4 catalyst has demonstrated good catalytic activity and selectivity in the process of conversion of cinnamaldehyde to cinnamyl alcohol,but the provision of external H2 is mandatory during hydrogenation reaction.It has been reported that the selective hydrogenation of unsaturated aldehydes or ketones can be achieved by Meerwein-Ponndorf-Verley(MPV)reaction in the presence of 2-propanol as a hydrogen transfer agent(such as isopropanol,etc.).In this section,the activated carbon with large specific surface area and porous structure has been used as substrate to load Pt/Fe3O4 nanoparticles fabricated by a spontaneous redox reaction.The porous structure of activated carbon is favorable for mass transfer of the reactants and high surface area is beneficial to the exposure of catalytic active sites.The results demonstrated that the obtained catalyst can afford a high selectivity of cinnamyl alcohol with 95%under the conditions of 393 K for 6 h with isopropanol as a hydrogen transfer agent.4.The high active catalysts fabricated by universal synthetic methods are critically important for their large-scale applications.Therefore,we successfully prepared a variety of metal oxide-coated metal catalysts by a one-pot redox method,followed by combining these materials with activated carbon with large specific surface area to obtain activated carbon supported M/NOx catalysts(M = Pt,Pd,Ru,NOx = CeO2,Fe3O4).The results indicated that these developed catalysts all exhibited superior hydrogenation reduction activities toward different ?,?-unsaturated aldehydes,such as cinnamaldehyde,crotonaldehyde,citral,?-methyl cinnamaldehyde,2-methyl-2-pentenal and 3-(2-furyl)-propenal.This sectional work lays a solid foundation on different metal oxide-coated metal based catalysts fabricated by a facile spontaneous redox method for future large-scale applications.