Preparation Of Co And Ni Single Atom Catalysts Derived From ZIF-8 And Their Catalytic Performances

Single-atom catalysts（SACs）are a type of supported metal catalysts,in which the metal components exist in an atomically dispersed form on the supports.By virtue of the advantages of high activity,high selectivity and high atom utilization efficiency,SACs have exhibited excellent catalytic performance in diverse applications.Metal organic frameworks（MOFs）are considered to be good templates for the preparation of SACs due to the isolated metal oxides and ordered pore structures.Zeolitic imidazolate frameworks（ZIFs）,as a subclass of MOFs,are often used as precursors to derive SACs.The derived carbon materials from ZIFs not only have the abundant pore structures and the large specific surface area,but also are rich in N species that can be employed as anchor sites to stabilize the metal atoms.At present,nitrogen-doped carbon materials with hollow structures have attracted much attention due to their ability to intensify mass transfer and enhance catalytic performance.Therefore,this thesis aims to develop the nitrogen-doped carbon material supported non-noble metal single atom catalysts with hollow structures and apply them to the important catalytic hydrogenation reactions.This work starts from ZIF-8 and introduces Co²⁺and Ni²⁺through different methods to prepare PS@Zn Co-ZIF and PS@ZnNi-ZIF composites with a core-shell structure.Then,preparing Co single-atom catalyst（Co SAs/NHPCN）and Ni single-atom catalyst（Ni SAs/NHPCN）supported on the nitro genincorporated hollow porous carbon nanospheres through a high temperature pyrolysis strategy.X-ray powder diffraction,scanning electron microscopy,transmission electron microscopy,spherical aberration corrected transmission electron microscopy,N₂ absorption and desorption,Raman spectroscopy,X-ray photoelectron spectroscopy,X-ray absorption fine structure spectroscopy and other characterization techniques are used to systemically characterize the physical and chemical properties of the catalysts.Subsequently,the synthesized catalysts were applied to the catalytic hydrogenation of 2,3,5-trimethylbenzoquinone（TMBQ）to2,3,5-trimethylhydroquinone（TMHQ）and the selective hydrogenation of nitroaromatics to corresponding aromatic amine,respectively.Thus,non-noble metal-based SACs are developed.The main results of this thesis are summarized as follows:（1）A sacrificial template strategy was developed to fabricate a single-atom Co catalyst embedded on nitro genincorporated hollow porous carbon nanospheres（Co SAs/NHPCN）by direct carbonization of core-shell structured PS@Zn Co-ZIF composites.Next,the Co SAs/NHPCN is applied to the hydrogenation of TMBQ to TMHQ,an important intermediate of vitamin E.Compared to Co nanoparticle catalyst（Co NPs/NHPCN）,BMZIF-920 and Co-N-C without hollow structure,and Co/C without N in the framework,Co SAs/NHPCN showed the higher catalytic activity under the same reaction conditions.The catalytic activity is even higher than those Co-based catalysts reported in the literature.Its excellent catalytic reaction performance is mainly attributed to unique porous structure and Co sites in the form of Co N₃ configuration.In addition,Co SAs/NHPCN also exhibited superior catalytic performance for the selective hydrogenation of nitroaromatics to corresponding aromatic amines under moderate reaction conditions.（2）After the synthesis of PS@ZIF-8 precursor,a small portion of Zn²⁺in PS@ZIF-8 are controllable exchanged by Ni²⁺to obtain the PS@ZnNi-ZIF composites.Subsequently,the composites are carbonized at high temperature to derive Ni SAs/NHPCN with a hollow structure.Finally,the synthesized catalysts are applied to the selective catalytic hydrogenation of nitroaromatics to the corresponding aromatic amines.Under the mild reaction conditions,Ni SAs/NHPCN is capable of converting nitroaromatics to the corresponding aromatic amines efficiently with hydrazine hydrate as the hydrogen source.The excellent catalytic activity of Ni SAs/NHPCN is mainly attributed to the atomically dispersed Ni and the anchoring effect of N on the support to metal Ni.