Synthesis Of Single-Atom Pt Catalysts Using MOFs-Derived Materials As Templates And Their Hydrogenation Properties

Zeolitic imidazolate frameworks?ZIFs?are a class of novel zeolite-like materials with regular network structures formed by the self-assembly of inorganic metal ions and nitrogen-containing multidentate organic ligands through coordination.As a big branch of the metal organic frameworks?MOFs?materials,ZIFs have high specific surface area,adjustable pore sizes and pore shapes,and structural diversity,and the coordination atoms in organic bridging ligands are N-elements.After pyrolysis,some nitrogen-containing compounds or metal/carbon materials are available with special structural characteristics and abundant catalytically active sites.On the other hand,single-atom catalysts normally have higher catalytic activity and chemical selectivity as compared with nanoparticles due to their unique structural and electronic properties.As a new type of high-efficiency catalysts,development of novel single-atom catalysts has been an effective way to solve energy and environmental problems and thus is of great significance.The purpose of this thesis is to develop a novel preparation method for noble single-atom catalysts.The ZIFs-derived materials were used as sacrificial templates to prepare singl-atom Pt catalysts with a high loading by traditional metal displacement method.Their catalytic hydrogenation performances were also studied systematically.In this thesis,we choose Zn_xCo_y-ZIFs with low Co metal molar percentages as the precursors to prepare monoatomic Co-based material by direct pyrolyzation at a high temperature of 1000?.Then,a series of highly dispersed Pt single-atom catalysts on N doped carbon?Pt SAs-CN?were prepared by using a galvanic displacement method.The structure and properties of the synthesized Pt SAs-CN catalysts were analyzed by X-ray powder diffraction,specific surface area and pore size analysis,spherical aberration correction-transmission electron microscopy and X-ray photoelectron spectroscopy.The analysis results showed that Pt atoms catalysts prepared by this method were highly mono-dispersed in N-doped porous carbon carriers with a maximum loading of 2 wt%.In addition,the catalytic properties of Pt SAs-CN catalysts for hydrogenation of nitrobenzene to aniline were investigated.The analysis of the experimental results showed that single-atoms Pt catalysts exhibited high catalytic activity and selectivity at 30?and atmospheric pressure of hydrogen which acted as reducing agent.We proposed there were two main reasons for the high catalytic activity.On the one hand,from structural characteristics aspect,the Pt active component was mono-dispersed in the N-doped carbon material,which greatly increases the catalytic active sites.In addition,the porous carbon material carrier has a high specific surface area and abundant pore structure provides more reaction sites for the reactants;On the other hand,from unique electronic property aspect,the effect of the size effect on the interaction between the Pt single atoms and the support,and the metal substitution for the introduction of the metallic Pt single atom,XPS results showed that Pt in single atom catalyst is in a metallic state,and its electron density is larger than that single atom Pt that reported in reported literatures,thus leading to a stronger interaction with H₂.