Precise Construction And High Selective Hydrogenation Performance Of Carbon Modified Pt Based Catalysts

When the substrate contains two reducible functional groups,selective hydrogenation refers to the ability to selectively hydrogenate only one functional group,or the capacity to stop the hydrogenation at the alkene stage when the substrate contains alkynes,rather than directly hydrogenating to the alkyl group.Catalytic hydrogenation of nitroaromatic hydrocarbons to produce aromatic amine intermediates is one of the significant reactions in the chemical industry.The product is diffusely used in the fields of rubber,dyes,pharmaceuticals,and polymer materials.However,when the nitroarene substrate contains both halogen groups or other reducible groups（such as-C=C,C=O,and C≡N）,the problems of dehalogenation and excessive hydrogenation are prone to occur during the catalytic reaction process,resulting in a significant challenge in the selective hydrogenation of specific groups.At the same time,phenylacetylene is also easily hydrogenated to ethylbenzene,resulting in a decrease in selectivity.This necessitates the development of heterogeneous catalysts that offer high activity,selectivity,and stability.Pt-based catalysts have gained considerable attention for their ability to selectively hydrogenate under mild conditions,making them a valuable choice for researchers.In this thesis,a platinum based catalyst with dual active sites（titanium oxide and graphite carbon coated Pt NPs and highly dispersed Pt single atoms）was synthesized for the first time through a CO high-temperature induction strategy.The morphology,structure,and active sites of the synthesized catalyst were characterized in detail using various characterization techniques.The synthesized Pt catalyst was used in the model reaction of selective hydrogenation of nitroaromatic hydrocarbons and semi-hydrogenation of phenylacetylene,The results show that the prepared catalyst has unique advantages in catalytic activity,selectivity,and stability.This research introduces a fresh synthesis approach for modifying Pt-based catalysts.The specific details of the work are as follows:（1）A novel Pt/TiO₂-TCO catalyst（where T represents the temperature of the heat treatment;CO represents the CO atmosphere）was initially prepared by simple CO gas heat treatment of Pt/TiO₂ precursors at different temperatures.The catalyst exhibited unprecedented selectivity and stability for the hydrogenation of 4-nitrostyrene（4-NS）with 4-vinylaniline（4-VA）.A series of comprehensive and in-depth structural analyses show that the Pt species in Pt/TiO₂-TCO catalysts（T≥600℃）mainly exist in two types,namely,a large number of atomically dispersed Pt atoms and Pt NPs covered with amorphous TiO_x and graphitized carbon（TiO_x&C）coatings.Detailed mechanism studies such as H/D exchange and site selective poisoning have confirmed that the above two active components play a unique catalytic role in the selective hydrogenation of 4-NS.Specifically,the superior hydrogenation selectivity comes from the reversible process of rapid insertion and subsequent elimination of H atoms at the-C=C bond adsorbed on the single atom Pt site,while the TiO_x&C coating layer has selective permeability to the-NO₂ group.（2）1 wt%Pt/TiO₂ precursor was synthesized by the impregnation method,and then exposed to CO atmosphere for pretreatment.Parameters such as exposure time,gas flow rate,and temperature were adjusted to deposit different amounts of carbon species on the surface of Pt/TiO₂ to obtain a Pt/TiO₂-TC catalyst.The results of Raman spectroscopy,elemental analysis,and in situ CO DRIFTS spectroscopy confirmed that CO was deposited on the catalyst surface through the Boudouard reaction（2CO→C+CO₂）.The electronic structure of Pt was accurately analyzed using X-ray absorption fine structure（XAFS）.Through experimental comparison,we found that compared to Pt/TiO₂-TH prepared under the same conditions,the catalyst had a significant improvement in the selective hydrogenation of phenylacetylene,from 35%selectivity to 84%selectivity.This may be due to the formation of a dual active site Pt catalyst after treatment in a CO-reducing atmosphere.The interaction between Pt NPs coated with TiO_x&C and monodisperse Pt atoms makes it have high conversion and selectivity.