Construction Of 2D MoS₂ Edge-Confined Single/Dual Atom Catalysts And Study On Hydrogenation Performance

Hydrogenation is one of the significant reactions in the production of chemical industry,a series of high-value products like food additives,fuels,agricultural chemicals,fine chemicals and medicines can be synthesized by catalytic hydrogenation,involving all directions of humanity’s life.Nowadays,heterogeneous catalysts represented by supported metal catalysts are widely used in selective hydrogenation.The selectivity and activity of hydrogenation reaction can be further improved by adjusting and designing the surface/interface structure of supported metal catalysts,but there exist still a few matters and challenges.For example,the traditional supported nanoparticle catalyst has a low metal atom utilization rate,resulting in a large amount of metal waste.In addition,it is difficult to control the high dispersion and uniformity of metal active species,which leads to the existence of multiple adsorption configurations of the substrate molecules,affecting the selectivity of the products.Therefore,atomic-supported metal catalysts with maximum atomic utilization and high uniformity are developed and designed to enhance the catalytic performance of selective hydrogenation,which is a research direction with theoretical research purport and practical use worth.According to the above issues,this paper use a thin layer of two-dimensional（2D）MoS₂material with 1T phase as the carrier,and the single/double atoms metal species are anchored at the edges of 2D 1T-MoS₂ to synthesize two supported metal catalysts（Pt₁/1T-MoS₂ single atom catalyst（SAC）and Rh₂/1T-MoS₂ dual atom catalyst（DAC））,which enhance the catalytic performance of the selective hydrogenation of maleic anhydride,dimethyl oxalate and 3-nitrostyrene.By characterization methods of high angle annular dark field scanning transmission electron microscope（HAADF-STEM）,in situ diffuse reflection fourier transform infrared（in-stiu DRIFTS）,kinetic analysis and density functional theory calculation,the structure-activity relationship between the structural characteristics of the atomic-level active sites of the catalyst and the hydrogenation performance is studied,and the reaction mechanism of the hydrogenation process is further revealed.The specific work contents and results are summarized as follows:（1）Pt₁/1T-MoS₂ SAC is prepared by anchoring a single Pt atom on the edges of 2D 1T-MoS₂ nanosheets by adsorption method,which shows 100%conversion and selectivity in the selective hydrogenation of maleic anhydride to succinic anhydride.In addition,the turnover frequency calculated based on Pt atom is much higher than the reported optimal homogeneous and heterogeneous catalysts.The experimental data and theoretical calculations show that the edge-anchored Pt₁ active site has a geometric configuration resembling a"pocketlike"（HO-Mo-S-Pt₁-S-Mo-OH）,edge steric effects can control the adsorption configuration of maleic anhydride molecules to achieve the formation of the target product.In addition,Pt single atom with electron-deficient characteristics is conducive to the activation of H₂.The strategy of constructing edge-confined active sites using specific phase 2D thin layer nanomaterials and metal single atoms introduced in this chapter provides an effective way to improve the catalytic activity of biomass derivatives conversion.（2）Rh₂/1T-MoS₂ DAC is prepared by anchoring Rh species with dual atom form on the edges of 2D 1T-MoS₂ nanosheets by adsorption method.Under mild reaction conditions（1MPa H₂,240℃）,Rh₂/1T-MoS₂ DAC has excellent catalytic activity(TOF 6879.2 h^-1),selectivity（96.5%）and stability for the industrial important hydrogenation of DMO to ethanol.In situ characterization and theoretical calculation show that the steric hindrance generated by the edge-anchored Rh₂active site（HO-Mo-S-Rh₂-S-Mo-OH）further regulates the adsorption mode of dimethyl oxalate,which is conducive to the activation of DMO molecules.Moreover,Rh dual-atom active sites enhance the dissociation ability of H₂ and promote the hydrogenation reaction.The metal dual-atom catalysts anchored on the edges of 2D thin layer nanomaterials constructed in this chapter provides a good idea for the synthesis of high-efficiency hydrogenation catalysts.（3）Based on the structural characteristics of the edge-anchored Rh₂/1T-MoS₂ DAC prepared in the second part,it is further extended to the selective hydrogenation of the nitro group in the 3-nitrostyrene molecule.At room temperature,Rh₂/1T-MoS₂ DAC can completely convert 3-nitrostyrene and generate 3-vinylaniline with 100%selectivity.Theoretical calculation shows that the nitro group is adsorbed on the Rh dual-atom site in a bidentate configuration and hydrogenated in a dynamic structure similar to a"seesaw"（i.e.,the molecule jumps between the two Rh sites）,which is conducive to reducing the apparent potential energy of the hydrogenation of 3-nitrostyrene.The work in this chapter further proves that the strategy of designing edge-anchored metal dual-atom catalysts has certain applicability for improving the selective hydrogenation performance.