Synthesis Of SAPO-based Single Atom/Cluster Catalysts And Investigation Of Their Catalytic Performance

In recent years,supported single atom/cluster catalysts have the characteristics of high activity,high selectivity and high stability,and have great potential for use in hydrogenation,oxidation and other catalytic reactions.They have become a new research hot-spot in heterogeneous catalysis.The purpose of this thesis is to propose a novel synthesis method of single atom/cluster catalyst and explore its mechanism in selective hydrogenation catalysis.The isolated palladium metal atoms and clusters are loaded on SAPO-31 by the atomic scale confinement strategy and photochemical strategy,respectively.The physicochemical properties and catalytic properties of the catalysts are studied by advanced characterization methods.The catalysts showed excellent catalytic activity,selectivity and cycling stability in the selective hydrogenation reactions.The catalysts maintain their high atomic dispersion at high temperatures,and there is no obvious phenomenon of metal species agglomeration,featuring promise for potential applications.This paper mainly includes the following aspects:1.Palladium-based single atoms supported over SAPO-31 catalysts were synthesized by atomic-scale confinement strategy.Utilizing high-resolution transmission electron microscopy,X-ray photoelectron spectroscopy,and near-range X-ray absorption fine structure spectroscopy,it was confirmed that palladium single atom was uniformly dispersed on SAPO-31.Based on the theoretical calculation,the supported palladium atoms were found to be isolated in the 12 rings of SPAO-31 and coordinate with two oxygen atoms.The results of catalytic performance tests show that the catalyst has excellent selective catalytic performance for hydrogenation of styrene(750 h^-1),phenylene(2223 h^-1)and 1-chloro-4-acetylenyl benzene(2000 h^-1),and has no performance decay in recycling tests.Besides,the catalyst can still maintain the high dispersion of the palladium active sites at high temperatures,and there is no obvious metal agglomeration occurred.2.A photochemical strategy was proposed to construct palladium nanoclusters over the SAPO-31.In the synthesis,the palladium precursor was slowly reduced over SAPO-31 by ultraviolet irradiation.The coordination environment of the central metal atom was controlled by optimizing the concentration of the metal salt solution,reaction temperature,reaction time,and other parameters.In combination with theoretical calculation,the use of high-resolution transmission electron microscopy,spherical aberration correction electron microscopy,X-ray photoelectron spectroscopy,and near-range X-ray absorption fine structure spectroscopy confirmed that the active sites in the form of palladium nanoclusters distribution outside the SAPO-31 channel,with a small fraction of the isolated palladium atoms confined within the channels of SAPO-31.The catalyst showed excellent catalytic activity,selectivity,and stability in the selective hydrogenation of styrene(2500 h^-1),phenylene(26110 h^-1),1-chloro-4-acetylenyl benzene(6000 h^-1),and vanillin(1715 h^-1).Its excellent catalytic performance can be attributed to the presence of more reactive sites in the catalyst,which further demonstrates the application potential of the nano-cluster catalyst supported by molecular sieve in catalysis.