Synthesis Of Oxygen Deficient Oxides Supported Pd Nanocatalysts And Their Applications In Hydrogenation

Catalytic hydrogenation is one of the most important processes in organic synthesis.It has been widely applicated in pharmaceutical industry,energy conversion,fine chemicals production and petrochemical industry,and it is also closely related to the industrial production and People’s Daily life.The catalytic hydrogenation reaction is low cost input,high atomic economic efficiency,superior product quality and small environmental impact,which meets the demand of sustainable development of contemporary society and can reduce the discharge of waste residue,waste water and waste gas in industrial production while reduce the impact of economic development on the environment.However,the development of catalytic hydrogenation technology strongly depends on the design of catalysts.Traditional hydrogenation catalysts rely on harsh reaction conditions,and their catalytic performance including activity,stability and selectivity are far from satisfactory.Therefore,it is urgent to develop new hydrogenation catalysts with excellent catalytic performance.Supported Pd-based nanocatalysts have the advantages of low cost,high activity,good selectivity,and easy recovery.Therefore,the design,preparation and optimization of supported Pd-based nanocatalysts has been one of the hotest topics in catalytic hydrogenation research in recent years.Oxygen deficient oxides can form strong interaction and electron interaction with metal species,which may contribute to the improved the catalytic performance.The aim of this paper is to design and synthesize Pd-based nanocatalysts supported by oxygen deficient oxides,and explore its application in catalytic hydrogenation reactions.The details are as follows:In chapter 2,we have synthesized oxygen deficient CeO2-x supported Pd nanocat-alyst via impregnation-reduction method,and successfully applied it to a novel and reversible color switching system based on one-pot hydrogenation/oxygenation reac-tions of redox dye.The obtained Pd/CeO2-x shows highly efficient hydrogenation of thionine(TH+)and the original purple color of TH+can fade rapidly and completely in 1 atm H2,while the resulting colorless leuco thionine(LTH)can reversibly and quickly switch to purple TH+ by oxygenation in 1 atm O2.In comparison with the reported color switching systems based on photoisomerization of chromophores,our Pd/CeO2-x/thionine/HEC system exhibits highly efficient catalytic activity and recyclability,as the switching cycles can be performed for more than 10 times without apparent fatigue.The Pd catalyzed hydrogenation of CeO2 generates an oxygen-vacancy-rich CeO2-x support.A synergistic effect between abundant oxygen vacancies and strong metal-support interaction has been well established,which is responsible for the superior catalytic performance.We anticipate that our efficient reversible color switching system may find potential applications including oxygen indicators for food packaging,security inks,rewritable papers and efficient organic transformations.In chapter 3,we have successfully fabricated the first example of a novel,highly efficient and long-lasting Ni-CeO2-x/Pd nanocatalyst,which can be conveniently separated from the reaction system by a magnet.The optimal 61 wt%Ni-CeO2-x/Pd nanocatalyst shows outstanding catalytic activity and excellent reusability compared to other reported catalysts toward the hydrogenation of 4-NP and styrene.The excellent performance of Ni-CeO2-x/Pd nanocatalyst can be mainly attributed to the following aspects:a)Hybrid nanostructures composed of oxygen deficient CeO2-x and metal nanoparticles are beneficial for reactant diffusion and active site exposure.b)Abundant oxygen vacancies produced by Pd-catalyzed hydrogenation of CeO2 and the strong metal-support interaction can facilitate electron transfer during the hydrogenation reactions.c)Ni species could form a charge-transfer complex with the benzene ring,which could strengthen the interaction between reactant and catalyst surface.Therefore,the Ni-CeO2-x/Pd nanocatalyst may endow a wide range of potential applications in catalysis,especially in the recyclable and efficient catalytic production in organic chemistry,environmental chemistry,and biological chemistry.Moreover,the design and synthetic strategy developed in this work could be extended to prepare other highly efficient,long-lasting,and easily recyclable catalysts for organic transformations.In chapter 4,we have firstly synthesized oxygen deficient Tb4O7-x supported ultra-small Pd nanoparticles and successfully applied it to the hydrogenation and cross-coupling reactions.With the help of Pd-Tb4O7-x nanocatalyst,the hydrogenation of 4-NP and styrene proceeded rapidly and efficiently to produce 4-AP and ethylbenzene in high yield,and the suzuki corss-coupling of aryl halides with phenyl boronic acid also provided biphenyl in good yield with high TOF values.Additionally,the Pd-Tb4O7-x nanocatalyst also exhibited good recyclability,no obvious decrease in activity could be observed after many successive cycles.The enhanced catalytic performance of our Pd-Tb4O7-x nanocatalyst can be attributed to the small size of supported Pd NPs,the contribution of oxygen vacancies on Tb4O7-x support,as well as the strong metal-support interaction and electron communication between Pd and TbaO7-x support.Our study provides a new insight into the design and development of metal nanoparticles on oxygen deficient Tb4O7-x support,affording strong metal-support interaction and electron communication between metallic Pd and Tb4O7-x support.We anticipate that the oxygen deficient TbaO7-x supported palladium or other metal nanoparticles could be explored as promising hybrid nanocatalysts for various catalytic reactions.