Theoretical Prediction Of The Electrocatalytic Activity Of Two-dimensional Materials Towards The Reduction Of Nitrobenzene To Nitrile

The hydrogenation of nitrobenzene is of great industrial significance for the synthesis of valuable intermediates such as aniline,hydroxylamine,azo and azo compounds.More importantly,the reduction of nitrobenzene to aniline is one of the most important chemical reactions in synthetic organic chemistry for the manufacture of agrochemicals,pharmaceuticals,dyes and pigments.However,Ph-NO₂ is a pollutant that seriously affects human health and the environment.Therefore,the efficient degradation of Ph-NO₂ is an important issue in the environmental field.Therefore,in recent years,nitrobenzene conversion has attracted extensive attention of scientific researchers from all over the world.Electrochemical methods have been regarded as one of the effective means to solve the energy and environmental problems faced by mankind due to their advantages of being able to perform under mild conditions,low consumption,and cleanliness.However,currently commonly used NBER catalysts are mainly based on transition metals,which often face the disadvantages of high cost,low content,and low catalytic efficiency,which greatly limit their large-scale applications.Therefore,while maintaining the high catalytic activity of these noble metal catalysts,it is necessary to minimize their dosage to achieve high-efficiency conversion of nitrobenzene.Single-atom or sub-nanoscale metal clusters are a new class of electrocatalysts in recent years.They have the advantages of maximum atom utilization and high catalytic activity,and have been widely used in the field of electrocatalysis.However,in the process of application of this type of catalyst,a certain carrier is required to enhance its stability.Therefore,the development of inexpensive new catalysts with high stability,high activity,and high selectivity is a challenge in the field of electrocatalytic nitrobenzene.Two-dimensional materials are considered as one of the ideal metal nanoparticle carriers due to their large specific surface area.In order to develop electrocatalysts for nitrobenzene reduction with high stability and high catalytic activity,we investigated single-metal supported on nitrogen-doped graphene（TMN₃/G）and C₂N supported on Pt clusters（Pt_n/C₂N（Pt_n,n=1～6,13））as effective electrons by density functional theory.The catalyst was used in the NBER process,and the specific results were as follows:（1）We proposed several single transition metal（TM）atoms embedded into the single vacancy of graphene with nitrogen-doping（TMN₃/G,TM=Ni,Cu,Pd,and Pt）as the catalysts for NBER.The electrocatalytic activity of these single-atom catalysts for NBER was investigated by high-precision density functional theory calculations.The results show that these N-doped graphene-supported metal single atoms have excellent environmental stability due to the strong hybridization between the metal single atom d orbital and the N atom 2p orbital in the support.On this basis,we calculated the Gibbs free energies of each step of the NEBR reaction on these catalysts,and evaluated the catalytic activity of these catalysts.Among these candidate catalysts,Pt N₃/G is the most active catalyst for NBER and follows the lowest energy path:Ph-NO₂^*→Ph-NOOH^*→Ph-NO^*→Ph-NOH^*→Ph-N^*→Ph-NH^*→Ph-NH₂^*→Ph-NH₂,in which the key intermediate Ph-NOOH^*is formed with a smallest limiting potential of-0.21V for this step.In order to deeply understand the excellent catalytic activity of single-metal Pt atoms in NEBR,we investigated the structure-activity relationship between the adsorption strength of key intermediate species in NEBR on the surface of each catalyst and the electronic structure of the catalyst,we analyzed the intrinsic relationship between the adsorption energy of Ph-NOOH^*on the surface of Pt_n/C₂N and the active site d-band center.The results show that the catalytic activity is related to the binding strength of the intermediate species Ph-NOOH^*on the catalyst surface,and the moderate binding strength between Pt N₃/G and Ph-NOOH^*is the reason for its excellent NBER catalytic activity.（2）Nanoclusters of Pt₁～Pt₆ and Pt₁₃ were embedded on the surface of two-dimensional C₂N materials as NBER electrocatalysts,and their stability and electrocatalytic performance in NBER were evaluated.Our results show that these Pt_nclusters anchored on the surface of the 2D C₂N support have considerable adsorption energies（3.81～7.68e V）,which guarantees their high stability.Subsequently,we further investigated the adsorption behavior of Ph-NO₂ reactant on the catalyst surface and found that Ph-NO₂ tended to be adsorbed on the catalyst surface in parallel.Further,by calculating the Gibbs free energy change of each elementary reaction in the electroreduction of nitrobenzene,we investigated the electrocatalytic performance of these Pt_n/C₂N.The results show that Pt₃/C₂N has the smallest limiting potential（-0.19V）,and thus exhibits extremely high catalytic activity towards NBER.Subsequently,in order to gain an in-depth understanding of the difference in the catalytic activity of Pt_n/C₂N for Ph-NO₂ electroreduction,we analyzed the intrinsic relationship between the adsorption energy of Ph-NOOH^*on the Pt_n/C₂N surface and the active site d-band center.The results show that the adsorption energy of Ph-NOOH^*species shows a clear linear relationship with the active site d-band center value,which well explains the origin of the excellent catalytic activity of Pt₃/C₂N.In summary,by studying the electrocatalytic performance and mechanism of NBER,we found that Pt N₃/G and Pt₃/C₂N are very promising metal electrocatalyst candidates among nitrogen-doped graphene supported metal single-atom catalysts as well as C₂N-supported platinum nanocluster catalysts with ultra-high catalysis for NBER active.This paper not only provides deeper insights into the reduction pathway of NBER,but also opens a new avenue for designing metal single-atom as well as metal nanocluster electrocatalysts for NBER.