Precise Synthesis Of Pd And Fe-based Single Atom Catalysts And Their Mechanisms Investigation On Catalytic Oxidation Reactions

Supported single atom catalysts have outstanding properties such as exceptional activity,high selectivity and excellent stability,and are widely used in catalytic reactions such as hydrogenation,oxidation,aromatization,cracking,etc.Therefore,developing novel synthetic methods for constructing single atom catalysts is of great importance.In this thesis,two types of single atom catalysts were prepared vis photoinduction and self-reduction synthesis strategies using γ-AlOOH and MoS₂ materials as supports,respectively.The morphologies and structures of catalysts were studied through a series of advanced characterizations.Importantly,they were successfully applied to catalyze the epoxidation of alkenes and the oxidation of alcohols,respectively.The main contents of this paper are listed as follows:A photoinduction strategy was employed to construct atomically dispersed palladium atoms supported over defect-containing boehmite（γ-AlOOH）nanoleaf with a palladium loading of 0.32 wt%.The existence of singly dispersed palladium atoms was confirmed by spherical aberration correction electron microscopy,extended X-ray absorption fine structure measurement,and CO-absorbed diffuse reflectance infrared Fourier transform spectroscopy.This catalyst shows excellent catalytic efficiency in trans-stilbene epoxidation to yield trans-stilbene oxide(TOF:416 h^-1;conversion:84%;selectivity:99%),along with excellent recyclability and scalability.In addition,various aromatic olefins were successfully transformed into the corresponding epoxides with high selectivity and excellent yield.The density functional theory（DFT）study further reveals that the high catalytic activity originates from under-coordinated single palladium atoms in the defect-containing γ-AlOOH in a unique coordination environment.This study lays the foundation for the facile creation of single atom catalysts and sheds light on the possibility of scale-up production.An efficient spontaneous reduction strategy was used to access atomically dispersed iron atoms supported over defect-containing MoS₂ nanosheets.Advanced characterization methods demonstrate that the isolated iron atoms situate atop molybdenum atoms and coordinate with three neighboring sulfur atoms.This Fe SAC delivers exceptional catalytic efficiency（1 atm O₂@120°C）in the selective oxidation of benzyl alcohol to benzaldehyde,with 99%selectivity under almost 100%conversion.TOF is calculated to be as high as 2105h^-1.Moreover,it shows admirable recyclability,storage stability,and substrate tolerance.DFT calculations reveal that the high catalytic activity stems from the optimized electronic structure of single iron atoms and the corresponding metal-support interactions.