Single‐atom catalysts(SACs)have demonstrated excellent performances in chemoselective hydrogenation reactions.However,the employment of precious metals and/or organic solvents compromises their sustainability.Herein,...Single‐atom catalysts(SACs)have demonstrated excellent performances in chemoselective hydrogenation reactions.However,the employment of precious metals and/or organic solvents compromises their sustainability.Herein,we for the first time report the chemoselective hydrogenation of 3‐nitrostyrene over noble‐metal‐free Co‐N‐C SAC in green solvent—compressed CO2.An interesting inverted V‐curve relation is observed between the catalytic activity and CO2 pressure,where the conversion of 3‐nitrostyrene reaches the maximum of 100%at 5.0 MPa CO2(total pressure of 8.1 MPa).Meanwhile,the selectivities to 3‐vinylaniline at all pressures remain high(>99%).Phase behavior studies reveal that,in sharp contrast with the single phase which is formed at total pressure above 10.8 MPa,bi‐phase composed of CO2/H_(2)gas‐rich phase and CO2‐expanded substrate liquid phase forms at total pressure of 8.1 MPa,which dramatically changes the reaction kinetics of the catalytic system.The reaction order with respect to H_(2)pressure decreases from~0.5 to zero at total pressure of 8.1 MPa,suggesting the dissolved CO2 in 3‐nitrostyrene greatly promotes the dissolution of H_(2)in the substrate,which is responsible for the high catalytic activity at the peak of the inverted V‐curve.展开更多
Gold catalysts have been reported as highly effective catalysts in various oxidation reactions.However,for chemoselective hydrogenation reactions,gold‐based catalysts normally show much lowercatalytic activity than p...Gold catalysts have been reported as highly effective catalysts in various oxidation reactions.However,for chemoselective hydrogenation reactions,gold‐based catalysts normally show much lowercatalytic activity than platinum group metals,even though their selectivities are excellent.Here,wereport that the chemoselective hydrogenation activity of 3‐nitrostyrene to 3‐vinylaniline overAu/TiO_(2)can be enhanced up to 3.3 times through the hydrogen reduction strategy.It is revealedthat strong metal‐support interaction,between gold nanoparticles(NPs)and TiO_(2)support,is introducedthrough hydrogen reduction,resulting in partial dispersion of reduced TiOx on the Au surface.The partially covered Au not only increases the perimeter of the interface between the gold NPs andthe support,but also benefits H_(2)activation.Reaction kinetic analysis and H_(2)‐D2 exchange reactionshow that H_(2)activation is the critical step in the hydrogenation of 3‐nitrostyrene to 3‐vinylaniline.Density functional theory calculations verify that hydrogen dissociation and hydrogen transfer arefavored at the interface of gold NPs and TiO_(2)over the hydrogen‐reduced Au/TiO_(2).This study providesinsights for fabricating highly active gold‐based catalysts for chemoselective hydrogenationreactions.展开更多
文摘Single‐atom catalysts(SACs)have demonstrated excellent performances in chemoselective hydrogenation reactions.However,the employment of precious metals and/or organic solvents compromises their sustainability.Herein,we for the first time report the chemoselective hydrogenation of 3‐nitrostyrene over noble‐metal‐free Co‐N‐C SAC in green solvent—compressed CO2.An interesting inverted V‐curve relation is observed between the catalytic activity and CO2 pressure,where the conversion of 3‐nitrostyrene reaches the maximum of 100%at 5.0 MPa CO2(total pressure of 8.1 MPa).Meanwhile,the selectivities to 3‐vinylaniline at all pressures remain high(>99%).Phase behavior studies reveal that,in sharp contrast with the single phase which is formed at total pressure above 10.8 MPa,bi‐phase composed of CO2/H_(2)gas‐rich phase and CO2‐expanded substrate liquid phase forms at total pressure of 8.1 MPa,which dramatically changes the reaction kinetics of the catalytic system.The reaction order with respect to H_(2)pressure decreases from~0.5 to zero at total pressure of 8.1 MPa,suggesting the dissolved CO2 in 3‐nitrostyrene greatly promotes the dissolution of H_(2)in the substrate,which is responsible for the high catalytic activity at the peak of the inverted V‐curve.
文摘Gold catalysts have been reported as highly effective catalysts in various oxidation reactions.However,for chemoselective hydrogenation reactions,gold‐based catalysts normally show much lowercatalytic activity than platinum group metals,even though their selectivities are excellent.Here,wereport that the chemoselective hydrogenation activity of 3‐nitrostyrene to 3‐vinylaniline overAu/TiO_(2)can be enhanced up to 3.3 times through the hydrogen reduction strategy.It is revealedthat strong metal‐support interaction,between gold nanoparticles(NPs)and TiO_(2)support,is introducedthrough hydrogen reduction,resulting in partial dispersion of reduced TiOx on the Au surface.The partially covered Au not only increases the perimeter of the interface between the gold NPs andthe support,but also benefits H_(2)activation.Reaction kinetic analysis and H_(2)‐D2 exchange reactionshow that H_(2)activation is the critical step in the hydrogenation of 3‐nitrostyrene to 3‐vinylaniline.Density functional theory calculations verify that hydrogen dissociation and hydrogen transfer arefavored at the interface of gold NPs and TiO_(2)over the hydrogen‐reduced Au/TiO_(2).This study providesinsights for fabricating highly active gold‐based catalysts for chemoselective hydrogenationreactions.
