Novel Porous Organic Polymer-supported Pd Nanoparticles For Alcohol Oxidation And Alkyne Hydrogenation

Palladium nanocatalysts have been widely used in alcohol oxidation and acetylene hydrogenation,but they have poor selectivity and stability.Porous organic polymer with excellent physical and chemical properties,such as high specific surface area,abundant impurity atoms,adjustable pore and high thermal stability,is a new kind of heterogeneous catalyst carrier.Thus,Pd-based catalysts can be prepared via a selectivity and stability improvement by the functional grous on the surface of porous organic polymer.Based on this,three novel functionalized porous organic polymer-supported palladium nanoparticles(Pd NPs)were designed and prepared for the selective oxidation of benzyl alcohol and the selective hydrogenation of alkynes,respectively.1.Porous organic polymers(IPTP)containing imidazolium ions and triazine ring units with high specific surface area were prepared by Debus-Radziszewski reaction.The supported Pd catalyst(Pd/IPTP)was prepared by ion exchange and in situ reduction between the precursor Na₂Pd Cl₄ and imidazole ions using the porous polymer as a support.The abundant imidazole units on the surface of IPTP provide an important anchoring site for the formation of ultra-small Pd NPs.The results show that the catalyst has excellent catalytic activity and selectivity in the selective oxidation of benzyl alcohol to benzaldehyde without the use of base and chemical oxidant.2.The imidazolium ion stabilized Pd catalyst(Pd/IHCP)was prepared by means of ammonia vaporization with Na₂Pd Cl₄ as the precursor.The imidazolium ion stabilized Pd catalyst(Pd/IHCP)was prepared by the free radical polymerization of the imidazolium ion unit.Compared with impregnation and reduction,Pd/IHCP catalyst prepared by ammonia evaporation method has excellent hydrogenation activity and selectivity in the selective hydrogenation of phenylacetylene.Through XRD,XPS and TEM characterization,it was found that there was charge interaction between the imidazolium unit on the surface of the support and Pd NPs,which improved the selectivity of Pd catalyst.The experimental results show that the synergistic effect between imidazolium unit on the surface of the support and Pd NPs also inhibits the aggregation and leaching of Pd NPs,thereby improves the stability of the catalyst.3.Cyclodextrin-based cross-linked porous organic polymers with high specific surface area were prepared by thiol-ene click reaction with divinylbenzene and CD-(SH)₇ as the building blocks,and it was used as a carrier to prepare Pd/PDVB-SH catalysts.The experimental results demonstrated that the sulfhydryl group in the CD-(SH)₇ unit can be used not only as an anchor point for Pd NPs,but also as a toxicizing agent.It showed excellent catalytic activity and selectivity in the selective hydrogenation reaction of phenylacetylene.