First-principles Study Of Single-atom Catalytic Reduction Of CO₂ And N₂O Based On C₂N

The trend of global warming is increasing,and reducing the concentration of greenhouse gases in the atmosphere has become an issue of increasing concern.Numerous researchers are working on converting greenhouse gases to reduce their concentration.The design and development of catalysts with high activity for catalytic conversion of major greenhouse gases are the important focus of research.In this thesis,I mainly studied the catalytic reduction of CO₂ and N₂O by the single atom catalyst based on C₂N monolayer.The main research results are:?1?In this work,the potential of Cu atom embedded C₂N monolayer?Cu/C₂N?,as a single-atom catalyst?SAC?for hydrogenation of CO₂ to formic acid,has been evaluated by the first-principles calculations.The computational results show that the reaction can proceed via two feasible mechanisms,which start from the initial co-adsorption of H₂ and CO₂ on Cu/C₂N?H₂+CO₂@Cu/C₂N?and H₂ adsorption on Cu/C₂N?H₂@Cu/C₂N?,respectively.Since the adsorption energy of the CO₂@Cu/C₂N system is-0.18 eV,Cu/C₂N is physically adsorbed to CO₂ and the adsorption system is unstable.So CO₂@Cu/C₂N was not considered as a reactant in the subsequent reaction.Mechanism II exhibits the obvious superiority due to the low barrier all through the whole channel.The highest energy barrier in mechanism II is only 0.53 eV,which is thermodynamically beneficial,which means that CO₂ hydrogenation to formic could be realized on the Cu/C₂N at the room temperature.The high activity of the single atom catalyst Cu/C₂N implies the potential application in the industrial CO₂ hydrogenation.This study also promotes a new path to design catalysts for the reduction of CO₂ and further broadens the range of applications for C₂N-based materials.?2?Since the single atom catalyst Cu/C₂N exhibits high catalytic activity in the reaction of CO₂reduction,we also used it in the reduction reaction of N₂O.In this reaction we also compared the catalytic activity of the noble metal catalyst Au/C₂N.The catalytic reduction of N₂O on the single atom catalysts Au/C₂N and Cu/C₂N can be divided into two mechanisms.The first mechanism is to adsorb N₂O on the catalyst initially.Then,N₂O decompose to N₂ and O-M/C₂N intermediate,and subsequently,adsorption of CO and O atom on the O-M/C₂N intermediate reacts to form CO₂.The second mechanism is to adsorb CO on the catalyst,followed by adsorption of N₂O,and then a one-step synergistic reaction to form N₂ and CO₂.The highest reaction energy barriers for the reaction on Au/C₂N and Cu/C₂N catalyst in mechanism I are 1.04 eV and 1.21 eV,respectively.The low energy barrier of mechanism I proved that mechanism I is more dominant in the reaction of catalytic reduction of N₂O.In addition,we can also see that the reaction energy barriers of the two catalysts in the mechanism I are approximate,that is,in the catalytic reduction of N2O,the catalytic performance of the non-noble metal single atom catalyst Cu/C2N is comparable to that of the noble metal single atom catalyst Au/C₂N.Our calculations can provide a theoretical basis for the catalytic reduction of N₂O,demonstrate that non-noble metals may have similar catalytic activity in the catalytic reaction with noble metals,and broaden the application of non-noble metal single atom catalysts.According to our calculation results,in the reaction of CO₂ and N₂O reduction,the inexpensive metal single atom catalyst Cu/C₂N has not only a lower reaction energy barrier but also a higher catalytic activity than other catalysts.In particular,the reaction of CO₂reduction to formic acid can be achieved at room temperature.