Preparation and Performance of Supported Rhenium Based Catalysts for Aqueous Hydrogenation of Dicarboxylic Acid
Supervisor:liang chang hai
Cellulose and hemicellulose can be converted into a variety of platform molecules.The utilization of these platform molecules as raw materials to produce chemicals can reduce the extra functionalization steps required for petrochemical feedstock and also provide a more diverse synthesis strategy.A dicarboxylic acid siuch as succinic acid is one of bio-platform compounds and can replace the existing C4-C6 platform molecule,existing a very significant application potential.Rhenium based catalyst has great application value in hydrogenation of dicarboxylic acid,due to its excellent catalytic performance and stability.This paper focuses on the preparation of supported rhenium-based catalyst and investigates the effects of support-metal interaction,intermetallic interaction and other factors on aqueous hydrogenation of dicarboxylic acid.Besides,the mechanism of dicarboxylic acid hydrogenation was also studied in order to achieve the aim of selective transformation.Monometallic Re/C catalysts are prepared with microwave assisted thermolytic method in order to obtain an effective catalytic system for aqueous hydrogenation of dicarboxylic acid.This method can avoid the use of solvent and significantly reduce synthesis time.Particle properties of as-prepared catalysts can be controlled by changing microwave irradiation time and then it will influence the active sites.The catalysts prepared with microwave method exhibit more active sites and higher catalytic efficiency than that prepared with impregnation method.Re/C catalyst will contribute to the production of tetrahydrofuran with a selectivity of 80%in aqueous hydrogenation of succinic acid.Additionally,the research on reaction pathway of succinic acid hydrogenation lays the foundation for the following work.Re-M(M=Ru,Pt and Rh)bimetallic catalysts with well structural properties are prepared with microwave assisted thennolytic method on the basis of the research above.Besides,hydrogenation mechanism of succinic acid is further studied and selective preparation of 1,4-butanediol is achieved.From our research,Re-M internietallic interaction can suppress hydrogenolysis performance of catalysts while maintaining high hydrogenation activity.It can also increase the reduction efficiency of metal species and enhance hydrogen activation ability,thereby further improving the catalytic activity.The research demonstrates that the selective hydrogenation of succinic acid is mainly decided by transformation of intermediate product y-butyrolactone.Re-M interaction can change the activation state of internediate product and hydrogen,consequently,promoting ring opening of y-butyrolactone to 1,4-butanediol.Furthermore,the influence of Re-M interaction with different species and strength on kinetic selectivity of 1,4-butanediol is very similar.In spite of this,Re-Rh/C and Re-Ru/C interaction cannot avoid the hydrogenolysis of 1,4-butanediol to n-propanol,thus limiting the selectivity of 1,4-butanediol compared with Re-Pt/C catalyst.Besides,low temperature is advantageous to ring opening of γ-butyrolactone to 1,4-butanediol and high temperature contributes to direct hydrogenation of γ-butyrolactone to tetrahydrofuran.The final selectivity of 1,4-butanediol can achieve 80%by controlling the reaction temperature according to the reaction mechanism.Regulation mechanism of intermediate on hydrogenation of dicarboxylic acid with different chain lengths are further studied.The research of Re based bimetallic catalysts is improved by the synthesis of Re-Ir/C catalysts.On this basis,the selective transformation of different dicarboxylic acid is achieved.Unlike other bimetallic catalysts,Ir component mainly acts as a hydrogen activator in the Re-Ir/C bimetallic catalyst,while Re component mainly:functions to adsorb dicarboxylic acid reactant and assist hydrogen activation.The adsorption of reactants and activation of hydrogen achieve a balance on Re-Ir(1:1)sample and Re-Ir interaction improves the catalytic activity most obviously.The difference in hydrogenation of succinic acid,glutaric acid and adipic acid is mainly caused by their different hydrogenation intermediates.The content of cyclic intermediate(γ-butyrolactone,etc.)gradually decreases with the increase of carbon chain length,however,the terminal hydroxycarboxylic acid(6-hydroxycaproic acid,etc.)in turn becomes dominant.Therefore,the influence of intermetallic interaction and reaction temperature on selectivity is more obvious for the reaction containing a cyclic intermediate,and an increase in linear intermediate makes the production of diol more advantageous with a selectivity of 90%.