Study On Selective Catalytic Reduction Of Biomass-derived Aldehydes Compounds In The Absence Of Hydrogen

Efficient conversion of biomass resources into liquid fuels and fine chemicals is an important way to achieve sustainable chemical production,and is also of great help on solving the energy crises and environmental pollution.At present,furfural,syringaldehyde and vanillin can be produced on a large scale using biomass as raw feedstocks.These compounds are often used as platform molecules because of their active aldehyde groups.Particularly,a series of high value-added chemical products can be produced through the hydrogenation,condensation and reductive amination reactions,etc..Therefore,the selective reduction of biomass-based aldehydes has important scientific value and application prospect.The work of this thesis aims to develop the suitable solid catalysts,which can efficiently promote the selective catalytic reduction of biomass derivatives.Moreover,the solid catalysts were characterized in detail,and the active catalytic site of the solid catalyst during reaction and reaction mechanism are further discussed.At first,we prepared a novel solid base catalyst containing active metal nanoparticles and alkaline earth metal oxide,and was used for catalyzing the hydrogen transfer reaction of furfural,where that the catalytic activity of Ni@R-Ca containing nickel nanoparticles was found to be the highest.When different alcohols were employed as solvent and hydrogen donor,the obtained main products include furfuryl alcohol（FA）and the condensation carbon-chain increasing product of the aldol condensation.Therein,when methanol is used as the solvent,a more than 99%selectivity of furfuryl alcohol can be obtained;while,when ethanol is used as a solvent,the furfuryl alcohol was generated as reduction product,along with the occurrence of3-（2-furyl）acrolein（FUA）as the condensation product.There is a similar phenomenon in the other alcoholic solvents.Then,the catalysts were characterized by FT-IR,XRD,BET,SEM,TEM and H₂-TPR techniques,etc..The surface basic sites and the base amounts of catalysts were measured by the Hammett indicator.The catalytic activity of catalyst has a high correlation with the number of basic sites on the surface.The characterization of various catalyst preparation processes shows that metals have an important influence on the formation of the surface base sites.The nickel metal particles on the surface of the catalyst greatly promote the formation of calcium oxide.The obtained Ni@R-Ca catalyst has a high specific surface area and high basic sites number,which play key roles in hydrogen transfer and aldol condensation reaction.Then,the ZrO（OH）₂ and ZrO₂ were synthesized by a simple method and used as catalysts for catalytic reductive amination of aromatic aldehydes.It was found that DMF can be used as the solvent,the amine source and the reducing agent.The aromatic aldehyde is almost quantitatively converted into the corresponding tertiary amine.In particular,when 3,4,5-trimethoxybenzaldehyde（TMB）is used as the substrate,the conversion can reach 95.8%,and the selectivity of the main product 3,4,5-trimethoxy-N,N-dimethylbenzylamine is 100%;in addition,when the biomass-derived vanillin is used as the reactant,the conversion of vanillin is 88.9%,and the selectivity of N,N-dimethyl-（3-methoxy-4-hydroxybenzyl）methylamine was81.8%.When syringaldehyde was used as the substrate,the reaction conversion rate was 85.8%,and the selectivity of product N,N-dimethyl-（3,5-dimethoxy-4-hydroxybenzyl）was almost100%.Furthermore,the catalyst was characterized by XRD,BET,SEM,pyridine adsorbed FT-IR;meanwhile,the isotopic control experiments were carried out.Based on the characterization data and the results of isotopic experiment,the catalytic reaction mechanism was proposed:First,the amide group was activated on the surface of zirconium oxide with the coordination function;subsequently,the hydrolysis followed to produce dimethylamine and formic acid.Next,the aldehyde group of the substrate and dimethylamine were reacted to form the Schiff base.Finally,the produced formic acid acts as the reducing agent to rapidly reduce the Schiff base to the corresponding tertiary amine and carbon dioxide.In summary,the reductive amination reaction employing the nano zirconia or zirconyl hydroxide as the catalyst,has the numerous advantages such as the mild reaction conditions,high reactivity and very good product selectivity,which is greatly suitable for the synthesis of dimethyl tertiary amine.