Design,Synthesis,and Performance Study Of Dual Site Catalytic Materials

Catalytic nanomaterials have an important role in oil refining,environmental protection,pharmaceutical production,and fine chemicals manufacturing.Constructing new catalytic systems and improving catalytic efficiency are effective means to increase the output and reduce industrial energy consumption,which requires a deep understanding of the structure-effect relationship between material surface structure and catalytic reaction mechanism.Coupling dual active centers provides an effective strategy to break the linear ratio of single site activity and break the performance limit.In recent years,with the development of nanotechnology,atomic-scale observation of material structure and real-time observation of reacting substrate molecular variations have been realized.Due to the complexity of the catalytic mechanism and the diversity of dual site catalytic nanomaterials,the research on dual site catalytic materials is still in its infancy,and it is still very challenging to tailor dual activity centers for specific reactions and maximize the synergistic effect between dual sites.In this dissertation,we designed and synthesized a variety of dual site catalytic nanomaterials with excellent performance for four typical catalytic reactions,including hydrogenation,oxidative coupling reaction,electron transfer reaction and reforming reaction,and explored the unique synergistic mechanism of dual site active centers in specific reactions by advanced structural characterization,in situ characterization combined with theoretical simulations.Our main achievements are as follows:1.We synthesized Fe-Pt/CeO2 dual site catalytic materials with Pt-O-Fe structure for the reverse water gas shift reaction via a simple impregnation method.The construction effectively solved the problem of low catalytic efficiency due to the unavailable excessive active hydrogen species.Thanks to the "two-way synergistic effect" between Fe and Pt,the CO2 conversion of dual site Fe-Pt/CeO2 in the reverse water gas shift reaction at 350℃ is as high as 21.3%,which is 1.5 times higher than that of the Pt single site.The TOFPt of Fe-Pt/CeO2 is as high as 43,519 h-1.The dual site catalyst can be recycled for 200 hours and maintain more than 80%of the initial activity.Mechanistic studies show that Fe can regulate the charge density of the adjacent Pt and promote the desorption of CO on Pt;the excess active hydrogen species produced on Pt sites can also activate the inert Fe to become highly active reverse water gas shift sites,thus enhancing the overall CO yield.2.We developed a ball milling-assisted solid phase single atom synthesis strategy and synthesized Co-SNC dual site catalytic material with Co-N4-S structure for the primary amine oxidative coupling to imine.The construction can effectively solve the problem of low imine yield due to the competitive adsorption between the primary amine substrate and oxygen molecules at the active center.The TON of Co-SNC is up to 190,which is 3.1 times higher than that of the Co-NC single site comparison sample and can be recycled more than 5 times.The Co-SNC also show excellent primary amine conversion and imine selectivity in the oxidative coupling reactions of other benzylamine derivatives.The mechanism study revealed that the addition of S could effectively adsorb and activate oxygen molecules,thus releasing the Co center for substrate primary amine adsorption.In addition,the method is universal and can achieve flexible combinations of different carriers and active centers.3.We further extended our ball milling-assisted solid phase single atom catalyst synthesis strategy to the oxide systems and successfully synthesized Pt-Ni dual single atom catalyst,which can effectively avoid active sites from coking during the methane dry reforming reaction.It was found that Ni in Pt-Ni dual atom active sites can promote Pt dispersion into single atom structures during the synthesis process,while Pt can further activate Ni to make it a highly active methane dry reforming reaction site,thus reducing the conversion temperature.The Pt-Ni/CeO2 sample is much more active than Pt/CeO2,with a lower T50 of about 175℃ and can work continuously for more than 130 hours.No carbon accumulation was found in the in situ Raman spectra,which confirmed the strong application of this synthetic strategy.4.We also designed and synthesized a Ce-Co3S4 dual site catalytic nanomaterial containing an abundant Co-Ce heterostructure interface.This material can induce the reduction of Co3+ at the interface to Co2+,thus enhancing the intrinsic oxygen evolution reaction activity of Co3S4.Meanwhile,the oxygen vacancies on CeO2 can also accelerate the key Volmer step in hydrogen evolution reaction,thus accelerating the reaction kinetics of hydrogen evolution reaction and making it a bifunctional water electrolysis catalytic material with intentional performance.The integration of the dual sites allows Co3S4 to reduce the overpotential by 170 mV in a fully cell and can operate continuously for more than 20 hours.