Design Of Supported Single Atom Catalysts And Their Application In Organic Transformations

In recent years,single atom catalysts have become one of the most active research frontiers in the field of heterogeneous catalysis due to their appealing application potential.In this thesis,we tried to explore efficient synthetic methods for preparing single atom catalysts and evaluate their catalytic performance in the C-C cross-coupling and olefin epoxidation reactions.Specifically,solid-state transformation strategy and co-precipitation strategy were developed to access Co and Ru-based single atom catalysts,respectively.A series of advanced characterization methods were conducted to evaluate the structural properties of the catalysts.The correlation mechanisms between catalyst structure and catalytic properties were discussed.The main points are listed as follows:1.Solid-phase conversion strategy was used to create a Co single atom catalyst anchored on nitrogen-doped carbon for C-C coupling reaction between benzyl alcohol and 1-phenyl ethanol.By means of high Angle dark-field scanning transmission electron microscopy,X-ray photoelectron spectroscopy,and near-edge X-ray absorption fine structure spectroscopy,the cobalt species that exist in the form of isolated metal atoms on the support was confirmed.The catalyst showed excellent catalytic activity(TOF=2307h^-1)and yield（95%）in the direct C-C coupling reaction of p-benzyl alcohol and1-phenyl ethanol to yield chalcone.This catalyst can be reused and has a good substrate scope.DFT calculation shows that the unique coordination environment,electronic structure,and strong metal-support interaction are the key to its high activity.2.Atomically dispersed Ru atoms supported on Bi OBr was prepared by coprecipitation method and used in olefin epoxidation reactions with high efficiency.The Ru atoms in the catalysts were characterized by high-resolution electron transmission electron microscopy,high angle dark-field scanning transmission electron microscopy,and electron paramagnetic resonance techniques.The catalytic performance results showed that the catalyst exhibited excellent catalytic activity(TOF=534 h^-1)and selectivity（99%）for the epoxidation of trans-stilbene,superior to most of those previously reported catalyst systems.Moreover,the catalyst can be used for at least ten cycles without any activity decay,along with a wide substrate scope.