Study On The Reaction Performance Of Supported Palladium Catalyst For Formic Acid Dehydrogenation And In-situ Hydrogenation Of Phenol

In recent years,hydrogen(H2),as a sustainable energy substitute for fossil fuels,has attracted extensive attention due to its excellent energy storage performance and clean reaction by-product(H2O).As an efficient raw material of chemical hydrogen storage,the technological difficulty is to promote the development of catalyst of formic acid decomposition.Palladiumbased catalysts are the most representative catalysts for dehydrogenation of formic acid.This dissertation firstly explores the effect of amine additives on the catalysis activity of sepiolite supported palladium catalyst,the further study of the effect of dual-support structure on the catalytic stability of MOF/sepiolite supported palladium catalyst is performed.Finally,the catalysis performance of formic acid dehydrogenation and in-situ hydrogenation of phenol over a novel porous carbon supported palladium catalyst at room temperature is studied.The results mainly include:1.The study on the effect of amine molecular structure on catalytic dehydrogenation of formic acid.Based on literature investigation and calculation of the hydrolysis rate constant and oil-water distribution coefficient of amines,it is found that amine molecules could interact with the functional groups on the surface of the support,thus affecting the reaction rate between the active center and reactants.By measuring the physical and chemical parameters(constant of reaction rate,chemical solubility,hydrophilicity)of different kinds of primary,secondary and tertiary amine,the promoting rule that molecular structure of amine affect catalytic process of formic acid dehydrogenation over sepiolite supported palladium catalyst is explored,and the semi-empirical dynamic model is established.By measuring the dissociation constant(Ka)and oil/water distribution coefficient(logP)of amine additives,the hydrogen production rate and apparent activation energy of the dehydrogenation system is calculated to comprehensively evaluate the promoting rule of organic amines on the catalysis system of sepiolite supported palladium,the optimal amine additives is screened and a new highefficient screening method of amine additive is developed.Thus,the kinetic behavior of basic additive promoting formic acid decomposition can be better predicted.2.Study on the influence of MOF/sepiolite dual-support structure on the stability of catalyst.In order to further improve the reusability of the sepiolite supported palladium catalyst in formic acid dehydrogenation,a dual-supported Pd-based catalyst can be synthesized by hydrothermal method,and metalorganic framework(UIO-66)can be grafted on the surface of amino-rich sepiolite.This study initially propose the sacrifice effect of the double supported structure,which is the self-sacrifice of the lamellar UIO-66 during the reaction,which protects the active center near the fibrous structure,thus maintaining stable catalytic activity and high reusability of the catalyst.The new dual-supported palladium catalyst has extremely high catalytic reutilization of more than 8 times with the maintaining of high catalytic activity.The characterization results show that there is no obvious agglomeration for the Pd particles near sepiolite.3.Study on the influence of the morphology of active sites on dehydrogenation performance of porous carbon supported palladium catalyst.The porous morphology and excellent pore connectivity of new carbon materials are conducive to effective diffusion and mass transfer between reactants and catalysts.Phosphoric acid is added as dispersant in the synthesis process of porous carbon supported palladium catalyst,the particle size of the active metal on the surface of the support is smaller with the more uniform distribution.In the decomposition process of formic acid molecules,proton tunnel is constructed for the transfer and bonding of proton,which can greatly reduce the reaction energy barrier.Combined with DFT(density functional theory)study,the Pd(100)crystal face on the surface of porous carbon support is more conducive to proton transfer and adsorption/desorption of hydrogen.The conjunction edge of the(100)and(111)crystal faces of Pd clusters are the key factors to lower the activation energy of the reaction,which results in the high activity of highly-dispersed Pd particles.4.Study on the influence of morphology of porous carbon supported palladium catalyst on in-situ hydrogenation of phenol.In the catalytic reaction of phenol hydrogenation to cyclohexanone,formic acid as an efficient Hdonor can provide hydrogen source for the in-situ hydrogenation process.Compared with sepiolite supported palladium catalyst,porous carbon supported palladium catalyst has higher reactivity in-situ hydrogenation reaction.The experimental results show that the smaller of the particle size of the active center is,the more(100)crystal surface will expose and finally reduce the energy barrier of the product-formation step,thus improving the hydrogenation rate of phenol.Under the optimum reaction conditions,the conversion of phenol is 80.99%and the selectivity of cyclohexanone is 90.20%.In conclusion,based on formic acid dehydrogenation and in situ hydrogenation of phenol over the novel sepiolite and porous carbon supported palladium catalysts,the high catalysis activity and stability is explained by the experimental data of catalytic activity and a variety of characterization methods(including TEM,FTIR,XRD,XPS,N2 ad sorption/de sorption experiments,etc.),the reaction mechanism of formic acid dehydrogenation and its application in in-situ hydrogenation of phenol is illustrated by DFT calculation.It is hoped that the new catalytic system can be applied to the industrialization of hydrogen energy.