The Study On Preparation Of Highly Dispersed Supported Noble Metal And Catalytic Hydrogenation Performance

Supported noble metal catalysts with excellent properties such as high activity,high selectivity and high stability are widely used in catalytic hydrogenation,oxidation,aromatization and cracking reaction.However,due to the noble metal reserves less and the noble metal catalysts reported in the literature are widely with low dispersion and low utilization rate of metal atoms,which leads to great restriction in the process of industrial application.Therefore,it is one of the hot topics in the field of catalysis to design high dispersion and high atom utilization of noble metal catalysts.Cinnamyl alcohol(COL)which is selectively hydrogenated of cinnamaldehyde(CAL)is an important pharmaceutical intermediate and food additive.Due to the presence of conjugated C=C bonds and C=O bonds in the structure of CAL,hydrogenation of C=C bonds with less bonding energy from the kinetic and thermodynamic is easier.At present,the catalyst has low selectivity and harsh preparation conditions,so the design of high conversion and high selectivity of the catalyst is still the main goal of the study.In this paper,the size controllable Fe(?)-Fe(?)LDH(GR)with high specific surface area were prepared by coprecipitation method.The Pt-based catalyst was obtained by loading Pt nanoparticles on the GR and applied to CAL hydrogenation reaction.It was found that the influence of the strong metal-support interactions(SMS1)on the catalytic performance.On the other side,the preparation method of a novel highly dispersed noble metal catalyst was proposed by using the properties of the tunable of the hydrotalcite lamellar element and the electron donation of Fe2+.Among them,the quasi-single atom Pt based catalyst was successfully prepared,showing high catalytic activity in the hydrogenation of o-chloronitrobenzene(o-CNB).(1)The GR nanosheets with honeycomb morphology and different sizes were successfully synthesized by adding different complexing agents.The resulting supported Pt catalysts over GR nanosheets were employed in the base-free selective hydrogenation of CAL to produce COL.The structure-activity relationship of the catalysts was studied by XRD,SEM,BET,XPS and CO-FTIR.The results show that the complexing agents hinder the agglomeration of GR nanosheets.With the different modes of action in the process of LDH growth,different size of nanosheets are obtained.High surface area and pore structure of the carrier is benefit for the disperse of Pt nanoparticles and diffusion of reactant molecules.On the other hand,The strong interaction between Fe2+ contained in GR and the active component and the strong reduction of the carrier greatly improve the selectivity of CAL hydrogenation to COL.Under mild reaction conditions(110 ?,1 MPa),both conversion and selectivity has reached more than 90%.(2)MgFe(II)Fe(III)LDH was synthesized by one-pot coprecipitation method,in which the ratio of Mg2+/Fe2+ was 10:1.Then the noble metal ions(Pt,Pd and Au)were adsorbed and further reduced by the electron donation of Fe2+ to obtain a highly dispersed noble metal catalyst where the Pt particles reach a quasi-single atomic scale.The results show that the nobel metal ions are recuced successfully by Fe2+ and attached to the carrier,in which the ratio of Fe2+ has a great influence on the particle size of noble metal.Moreover,the turnover frequency value(TOF)of the quasi-single atom Pt-based catalyst at the mild reaction conditions(40 ?,1 MPa)can achieve 28455 h-1,which showed excellent catalytic performance.