Studies On Themechanism And Confinement Theory For C₁ Reaction On Transition Metal Catalyst

One carbon?C₁?reaction is a chemical foundation for the efficient and clean utilization of coal and natural gas,including the efficient activation and directional conversion of C₁ molecules?such as CO and CH₄?on the metal catalysts.The development of the metal catalyst with the excellent performance is important,which plays a key role in the C₁chemical processes.It is an important way of improving the research efficiency of the new catalyst to understand the catalytic mechanism and realize the rational design of catalyst based on quantum chemical calculation.In recent years,the confinement theory for modulating the active site of the metal-based catalyst has been widely recognized in academia.The concept of intrinsic interaction proposed by this theory appears of great significance for basic theory of catalysis and rational design of catalyst.Based on density functional theory?DFT?calculation,the conversion of C₁molecules on different metal-based catalysts,including CO adsorption and dissociation under different CO covergaes on Ni catalyst,the reaction mechanism of CO hydrogenation to ethanol or C₂ oxygenate on Rh and Cu Co catalysts,the carbon deposition mechanism and the way to improve the anticarbon deposition in CH₄-CO₂ reforming reaction on Ni-based catalyst,and the diffusion mechanism of Cu and Rh surface active structures on Cu and Rh catalysts under CO,H₂ and H₂S atmospheres,were studied systematically at the electronic and molecular level.The descriptors of the intrinsic interaction for these processes were discussed.The results are as follows:1.CO adsorption and dissociation on Ni catalyst.The study shows that the saturation coverage on Ni?111?,?100?and?110?surfaces is 8/9,9/12 and 9/9ML,respectively.As the coverage increases,the adsorption energies decrease on the?111?and?100?surfaces,whereas the adsorption energy remains unchanged on the?110?surface.CO prefers to desorb from?111?and?110?surface under different coverages.However,on?100?surface,CO dissociation is more favorable than its desorption at the lower coverages?<3/12 ML?,CO prefers to desorb from surface at the higher coverages?<3/12 ML?.In this study,the adsorption enegy of C+O is regarded as the descriptor of the intrinsic interaction.It is positively correlated with CO dissociation barrier?R²=0.92?1.00?,that is,the smaller the adsorption enegy,the more difficult CO dissociation,i.e.the lower the activity.2.CO hydrogenation to ethanol on Rh catalyst.The activity and selectivity of CO hydrogenation were studied on FCC and HCP Rh crystal phases and surfaces by combining DFT calculations with microkinetic modeling.For CO dissociation,the?100?surface exhibits the highest activity among different surfaces,and FCC crystal phase has the higher activity than HCP crystal phase.The?311?surface exhibits the highest selectivity of ethanol,whereas the?100?surface exhibits the lowest.In this study,the adsorption enegy of CH_x+OH_y?x,y=0,1?is regarded as the descriptor of the intrinsic interaction.When the adsorption enegy of CH_x+OH_y is too big,CO dissociation activity is higher but the selectivity of ethanol is lower.When the adsorption enegy of CH_x+OH_y is too small,the selectivity of ethanol is higher but CO dissociation activity is lower.3.The formation of C₂ oxygenates from CO hydrogenation on Cu Co catalyst.The activity and selectivity of CO hydrogenation on Cu₂Co,Co₂Cu and Co₁₂/Cu catalysts were investigated using DFT calculations.The study shows that CH is the favourable CH_x species on Cu Co catalyst.As the adsorption strength of CH is enhanced,the activity of CH and CH₄ formation is improved while the activity of CH₃OH and C₂ oxygenate formation is suppressed.In this study,the adsorption strength of CH is regarded as the descriptor of the intrinsic interaction.The catalyst exhibits the best activity and selectivity of C₂ oxygenate at the moderate adsorption strength of CH of 6.78 e V.4.The anticarbon deposition mechanism in CH₄-CO₂ reforming reaction on Ni-based catalyst.The Ni@C catalyst was synthesized by traditional impregnation method and the catalytic performance was evaluated.The experimental results show that the Ni@C catalyst exhibits the high activity and anticarbon deposition performance.DFT calculations suggest that the nickel covered by graphene reduces CH₄ dissociation activity,and keep CO₂dissociation activity unchanged,which results in produing the enough O atoms to oxidize the C atom and avoid the carbon deposition.In this study,the adsorption enegy of CH_x?x=0-3?and CO_x?x=0,?is regarded as the descriptor of the intrinsic interaction.Only when the adsorption enegy of CH_x and CO_xreaches equilibrium,can the performance of the catalyst reach optimal.5.The diffusion mechanism of the surface active structure of Cu and Rh catalysts under different atmospheres.The results show that the diffusion rates of Cu and Rh surface active structure increase with the increase of temperature,which indicates that the deactivation of the catalyst is accelerated by the increase of temperature.Compared with vacuum condition,CO atmosphere inhibited the diffusion rate of Cu surface active structure,while H₂ had little effect on the diffusion rate of Cu surface active structure;CO and H₂ promoted the diffusion rate of Rh surface active structure.These results show that CO and H₂atmosphere can not promote the diffusion of Cu surface active structure and cause deactivation of Cu catalyst,while CO and H₂ atmosphere increase the aggregation tendency of Rh surface active structure and reduce the activity of Rh catalyst.Compared with CO and H₂,the trace H₂S accelerat the diffusion of Cu and Rh surface active structure to a great extent,and the diffusion rate of the surface active structure increases more obviously with the increase of H₂S concentration,indicating that the trace H₂S lead to the deactivation of Cu and Rh catalysts.6.The descriptors of the intrinsic interation for different C₁ reactions on the metal catalysts.Although the C₁ reactions and metal-based catalysts are different,all the descriptors are the adsorption energy of the related species concerning C and O.For a complete C₁ reaction process,the moderate adsorption energy of the related species concerning C and O can be used as the descriptors to describe the catalytic performance of the catalyst.