Preparation Of Carbon Supported Single-atoms Catalysts And Their Application In Organic Reaction

As the core of chemical catalysis,catalysts can effectively alter route of chemical reaction,optimize reaction conditions and obtain target products with high selectivity.Supported metal catalysts are widely used in chemical industry due to their high catalytic activity and selectivity.The catalytic activity of supported catalysts is closely related to the particle size of active metal,and the utilization rate of active center atoms is low.In order to improve the catalytic activity and the effective ratio of metal atoms,researchers have been reducing the particle size of the active metal center constantly until its limit,the single-atom catalysts?SACs?,where the active metal is dispersed on the carrier in the form of single atom.Carbon-based SACs mainly stabilize the metal atoms by introducing N atoms into the carbon framework and fixing the metal atoms on the carrier through strong coordination between N and active metal atoms.Due to unique structures of SACs,SACs of transition metals,such as Fe,Co,Ni,etc,have exhibited excellent catalytic activity and selectivity in hydrogen evolution reaction?HER?,oxygen evolution reaction?OER?,oxygen reduction reaction?ORR?,carbon dioxide reduction reaction?CO₂RR?,and organic catalytic reactions.Therefore,in this paper,Ni SACs?Ni-N-C?was prepared by high temperature pyrolysis with magnesium oxide as template,which was furtherly applied in organic catalytic reactions.The research contents are listed as follow:1. NiSACs with high nickel content?4.4 wt%?were prepared by pyrolyzing Ni source?NiCl₂?and organic ligand 1,10 phenanthroline?carbon source and nitrogen source?at high temperature,which were loaded on Mg O template.XRD,SEM,TEM,HAADF-STEM and other characterization methods have proved that Ni was atomically dispersed in the carbon skeleton.Synchrotron radiation analysis proved that Ni atoms were dispersed on the carrier via Ni-N bonding,and the coordination environment of Ni atoms in Ni SACs was obtained by fitting analysis.The Ni SACs were applied to the hydrogenation reduction of nitrobenzene,Ni-N-C-700 catalyst prepared at 700 ^oC showed highest catalytic activity and selectivity.The results of controlled experiments,synchrotron radiation analysis and DFT calculation showed that the excellent activity mainly result from the Ni-N₃ structure.The Ni-N-C-700 catalyst still showed excellent catalytic activity and selectivity after several cycles.Synchrotron radiation analysis proved that the coordination number of Ni–N reduced along with the temperature increase,and the change of coordination environment would have a great impact on the catalytic activity of Ni SACs.According to the above analysis,the coordination environment of SACs can be controlled by adjusting the pyrolysis temperature,furthermore,affecting catalytic activity of SACs catalyst.2. CuSACs were prepared by pyrolyzing Cu source?CuCl₂?and organic ligand1,10 phenanthroline?carbon source and nitrogen source?at high temperature,which were loaded on Mg O template.XRD,SEM,TEM and other characterization methods proved that Cu was atomically dispersed in the carbon skeleton.The Cu-N-C-800catalyst showed excellent activity and selectivity in oxidation of alcohols to aldehydes.At the same time,the Cu-N-C-800 catalyst still showed excellent activity after several cycles.The above experimental results provide a new route for regulating the activity center of carbon-based SACs.The application field of carbon-based SACs was expanded,and the high catalytic activity and selectivity of SACs were proved.