Preparation Of Pd Single-atom Catalyst And Its Application In Selective Hydrogenation Reaction

Supported noble metal catalysts exhibit excellent catalytic performance in most important chemical reactions and are widely used in industry,but noble metals are not inexhaustible,and their resources are scarce and costly.In the catalytic reaction of noble metal nanoparticle catalysts（NPCs）,only the metal atoms on the surface participate in the catalytic reaction,while the metal atoms inside do not participate in the reaction,which leads to an increase in the cost of the catalyst and a decrease in the utilization rate of metal atoms.One of the effective strategies to improve the metal atom utilization is to reduce the particle size.Dispersing noble metal particles into ultra-small forms can expose more active sites and can effectively utilize the catalytic active component to improve metal atom utilization and reduce production costs.Single-atom catalysts（SACs）offer maximum atom utilization,homogeneous active sites and a unique coordination environment.Atomic dispersion ensures that every metal atom is exposed to participate in the catalytic reaction,which is certainly attractive for cost-sensitive industries driven by precious metal catalysts.SACs have become the most attractive frontier in the field of multiphase catalysis and have received extensive attention and research.However,it is still extremely challenging to prepare simple,practical,stable and low-cost catalysts with high loading of noble metal atoms for the current synthesis strategy.In this thesis,atomically dispersed Pd catalysts were prepared using a simple nitric acid vapor method and applied to the selective hydrogenation of benzaldehyde and the selective hydrogenation of phenylacetylene to investigate the catalytic performance of Pd single-atom catalysts(Pd _SA/G).The study mainly covers the following aspects:（1）Pd nanoparticles catalysts(Pd _NP/G)were prepared by anchoring Pd nanoparticles in the defects of graphene using a deposition-precipitation method using graphene as a carrier.Then the nanoparticles were redispersed into single atoms using the nitric acid vapor method to obtain Pd _SA/G catalysts.Various characterizations of the synthesized Pd _SA/G catalysts showed that the Pd single atoms were uniformly dispersed on the graphene carrier.（2）The prepared Pd _SA/G catalyst was applied to the selective hydrogenation reaction of benzaldehyde to investigate its catalytic performance.And compared with the prepared Pd _NP/G catalyst,the study showed that the single atom exhibited better selectivity than the Pd _NP/G catalyst（97.45%）.（3）The prepared Pd _SA/G catalysts were applied to the selective hydrogenation of phenylacetylene to investigate their catalytic performance and stability.The study showed that the material has a high TOF value(36165 h^-1).