| In recent years,the "dual carbon" goal proposed by the state calls on all walks of life to reduce carbon dioxide emissions,which imposes more stringent requirements on the traditional petroleum energy field.In order to realize low-carbon and nocarbon energy utilization,the development of cleaner energy such as hydrogen energy is imminent.Liquid organic hydrogen carriers(such as toluene,dibenzyltoluene,Nethylcarbazole and other hydrogen storage systems)as a new form of hydrogen storage are more efficient than traditional hydrogen storage methods(high-pressure cylinder hydrogen storage,low-temperature liquid hydrogen storage,etc.)is more convenient and safer,which is conducive to the development and large-scale utilization of hydrogen energy.However,the existing liquid hydrogen storage catalysts are mainly supported metal nanoparticles.Since the hydrogenation and dehydrogenation reactions all occur on the surface of the metal nanoparticles,the internal atoms of the metal nanoparticles do not participate in the reaction,resulting in metal atoms.utilization is relatively low.At the same time,in the dehydrogenation reaction under high temperature conditions,the metal particles are prone to agglomeration,which further leads to the deactivation of the catalyst.Therefore,how to prepare stable,efficient and high atom utilization catalysts has received extensive attention.Single-atom catalysts(SACs)have received increasing attention due to their unique electronic properties,maximized atom utilization efficiency,and potential as a bridge between heterogeneous and homogeneous catalysis.However,SACs may have limited advantages and even limited applications for reactions that require designated metal states with multiple atoms or surface sites with metal-metal bonds.As a dimensional extension of the concept of SACs,fully exposed cluster catalysts(FECCs)offer diverse surface sites formed by ensembles of metal atoms for adsorption and conversion of reactants/intermediates.More importantly,FECCs have the advantage of maximizing atom utilization efficiency,and every metal atom in the active center can be used as an active site to participate in the catalytic reaction.The geometry and electronic structure of FECCs are different from that of bulk nanoparticles or SACs.In addition to the difference in electronic structure compared with bulk metal particle catalysts,FECCs differ from single-atom catalysts in the presence of metal-metal bonds and the presence of multiple Active catalytic sites for metal atoms that exhibit unique behavior in catalysis.However,the number of exposed atoms on the surface of metal particles tends to increase correspondingly with the decrease in size,and the surface energy also increases gradually,which leads to the fact that atomically dispersed FECCs catalysts are more likely to aggregate into large metal particles or larger clusters.Therefore,some strategies are needed to synthesize efficient and stable atomically dispersed metal catalysts.Based on this,in this paper,the surface defect-rich nanodiamond-graphene ND@G is used as a carrier,and its defect-rich graphene surface is used to anchor metal atoms,and atomically dispersed Pd and Ru are prepared by a simple deposition and precipitation method.The performance and application of atomically dispersed Pd-based and Ru-based catalysts in the field of liquid hydrogen storage were investigated.The research content of this paper mainly consists of the following two parts:(1)Two atomically dispersed Pd-based catalysts with different structures were synthesized on the ND@G support by adjusting the loading of metal Pd by the deposition-precipitation method,the single-atom catalyst 01Pd/ND@G and the fully exposed cluster catalyst 05Pd/ND@G,while the particle catalyst 05Pd-IM/ND@G was synthesized by impregnation method as a comparative sample.The successful synthesis of atomically dispersed Pd species was confirmed by means of spherical aberration electron microscopy and synchrotron radiation.The catalytic activities of the three Pd-based catalysts with different sizes in the toluene hydrogenation reaction are significantly different.From single-atom Pd,cluster Pd to particle Pd,the toluene hydrogenation activity shows a volcanic trend.The single-atom catalyst 01Pd/ND@G did not undergo toluene hydrogenation reaction,and the cluster catalyst 05Pd/ND@G showed the highest catalytic activity among the three.From the perspective of the adsorption and desorption of the substrate toluene on the catalyst,it is analyzed that this activity difference is related to the electron-poor and electron-rich state of the Pd species on the catalyst.By studying the catalytic toluene hydrogenation performance of three Pd-based catalysts,the structure-property relationship between the catalytic activity and size distribution at the atomic scale was constructed,which provided a good theoretical basis for further research and design of efficient toluene hydrogenation catalysts.(2)Different atomically dispersed Ru-based catalysts(01Ru/ND@G and05Ru/ND@G)were synthesized by the deposition-precipitation method,and the particle catalyst 05Ru-IM/ND@G was synthesized as a comparison.Performance test for catalytic toluene hydrogenation.The catalytic activities of the three catalysts also satisfy the distribution of the volcano curve.The fully exposed cluster catalyst05Ru/ND@G exhibits excellent catalytic hydrogenation performance,which is much higher than 01Ru/ND@G and 05Ru-IM/ND@G.Compared with other noble metal catalysts,the 05Ru/ND@G has significant advantages in activity,stability,and applicability under relatively mild conditions.The research results not only further confirmed the structure-property structure-activity relationship between the catalytic activity and metal size of atomically dispersed metal catalysts in the toluene hydrogenation reaction at the sub-nanometer scale,but also promoted the further application of atomically dispersed catalysts in the field of catalytic liquid hydrogen storage.development and application. |
PDF Full Text Request