Ultrafine Palladium Nanoparticle Supported On Functionalized Covalent Organic Framework And Its Catalytic Performance

Past decades,metal nanocatalysts have made major breakthroughs in basic research and practical applications in chemical industry.Research has found that there are many factors,including particle size,shape,chemical composition,metal-support interaction and metal-reactant /solvent interaction,etc.,affect the performance of metal nanocatalysts.Metal nanoparticles(NPs)with narrower particle size are considered to provide more active sites for catalysis,thereby making surface atoms more reactive,greatly improving atomic efficiency and reducing the cost of metal catalysts.Simultaneously,it was found that interactions such as synergistic effects,ligand effects and strain effects between metal NPs and supports also affect the catalytic performance of nanocatalysts.Therefore,it is of great significance to controllably synthesize metal nanocatalysts with excellent performance.Covalent organic frameworks(COFs)with high crystallinity and porosity connected by covalent bonds have extremely good application prospects in the field of chemical research,especially in the field of heterogeneous catalysis.The clear skeleton structure and regular pore structure make COFs as an ideal support for containing catalytically active sites.It is a meaningful study to synthesize supported precious metal nanocatalysts with high activity and high tolerance through design synthesis structured COFs,precise adjustment of the size and its distribution of metal NPs based on the interaction between the metal NPs and supports.In this context,several different COFs-supported Pd catalysts were designed and synthesized and applied to catalyzed different reactions.The main research contents of this paper are as follows:(1)Two kinds of triazinyl-functionalized COFs(TriazinylCOFs)with different pore diameters were synthesized by the condensation of cyanuric chloride with each of p-phenylenediamine and 4,4?-diaminobiphenyl.Based on the confined effect of the triazinyl-COF pore channel and the synergy between heteroatoms and metal NPs,a simple synthesis strategy was used to control the growth of Pd clusters,and the size of the Pd nanoclusters was about 0.8 nm.The obtained catalysts showed excellent catalytic activity in the reaction for reducing nitroaromatics.At the same time,the Pd@COF-BPh catalyst with larger pores has a better catalytic effect for the nitro reduction reaction than the Pd@COF-Ph catalyst due to the difference in pore size of the supports.(2)A highly stable azinyl-linked COF(ACOF)was synthesized from 1,3,5-tris(p-formylphenyl)benzene and hydrazine hydrate under solvothermal conditions.2D-lamellar structure and abundant azine groups make the prepared ACOF an ideal support for preparing heterogeneous catalysts for anchoring metal NPs.The Pd@ACOF catalyst prepared by successfully fixing highly dispersed ultrafine Pd NPs on nitrogen-rich crystals ACOF by a simple reverse double-solvent method showed excellent activity and stability for the Suzuki-Miyaura cross-coupling reaction.(3)Choose to synthesize cost-effective two-dimensional COFs(2D-COFs)containing triazine groups,and then self-template carbonize the 2D-COFs to make 2D nitrogendoped carbon nanosheets(NCNs),while using highly dispersed fine Pd NPs were modified to obtain Pd/NCNs catalysts.The prepared NCNs and Pd/NCNs have large specific surface areas and mesoporous and macroporous structures,which can enhance the diffusion and mass transfer of reactants.Pd/NCNs catalysts show excellent activity,stability and recyclability in the aqueous hydrodechlorination(HDC)of chlorophenols(CPs),which are organic harmful substances.At the same time,for the subsequent hydrogenation of the HDC product phenol to cyclohexanone,excellent activity and high selectivity were observed.In this paper,a series of Pd nanocatalysts were synthesized and applied by combining COFs with precious metal Pd NPs through different design ideas.This series of work expands the application of COFs materials in catalysis,and also provides a certain research foundation for the preparation and research of subsequent supported COFs nanocatalysts.