Applications Of Several 2d Materials In Small Molecule（CO,N₂） Catalysis:A First Principles Study

With a rising global population,increasing energy demands,and impending climate change,major concerns have been raised over the security of our energy future.Developing sustainable,fossil-free pathways to produce fuels and chemicals of global importance could play amajor role in reducing carbon dioxide emissions while providing the feedstocks needed to make the products we use on a daily basis.Over the past decade,substantial progress has beenmade in understanding several key transformations,particularly those that involve carbon,oxygen and nitrogen.The combination of theoretical and experimental studies working in concert has proven to be a successful strategy in this respect,yielding a framework to understand catalytic trends that can ultimately provide rational guidance toward the development of improved catalysts.Catalyst design strategies that aimto increase the number of active sites and/or increase the intrinsic activity of each active site have been successfully developed.The development of both experimental and computational methods that can rapidly elucidate reaction mechanisms on broad classes of materials and in a wide range of operating conditions（e.g.,pH,solvent,electrolyte）.Such efforts would build on current frameworks for understanding catalysis to provide the deeper insights needed to fine-tune catalyst properties in an optimal manner.The long-term goal is to continue improving the activity and selectivity of these catalysts in order to realize the prospects of using renewable energy to provide the fuels and chemicals that we need for a sustainable energy future.The rise of two-dimensional（2D）materials has led to the transfer of the catalyst study to2D materials,which is mainly due to the big surface/volume ratio of 2D materials.Many 2D materials,such as graphene,MoS₂,graphdiyne and C₃N₄,have always applied in the catalytic field.In this work,some 2D materials（MoS₂ and graphdiyne）are used as the substrates of active metal clusters or catalysts to catalyze small molecules.Moreover,we also design a new2D materials of MoC₆,which demonstrated outstanding catalytic activity for nitrogen reduction reaction.The main contents are divided into four parts:（1）The catalytic oxidation of CO molecule on a thermodynamically stable Cu₄ cluster doped MoS₂ monolayer is investigated by density functional theory where the reaction proceeds in a new formation order of COOOCO*（O₂*+2CO*→COOOCO*）,OCO*（COOOCO*→CO₂+OCO*）,and CO₂（OCO*→CO₂）desorption with the corresponding reaction barrier values of 0.220 eV,0.370 eV and 0.119 eV,respectively.Therein,the rate-determining step is the second one.This low barrier indicates high activity of this system where CO oxidation could be realized at room temperature（even lower）.As a result,the Cu₄ doped MoS₂ could be a candidate for CO oxidation with lower cost and higher activity without poisoning and corrosion problems.（2）Clusters with precise numbers of atoms can exhibit unique and unexpected properties due to their size-dependent active sites.Besides,to obtain the superior stability and catalytic activity,an appropriate substrate can prevent the metal clusters aggregating as well as change the geometric and electronic structures of metal clusters.In this study,the catalytic oxidation of CO on the Ag₃₈ cluster supported by graphdiyne(Ag₃₈-GDY)is investigated by density functional theory and molecular dynamics simulations,which provide an intensive understanding of its catalytic properties.Moreover,the process of CO oxidation on the Ag₃₈-GDY system has a high activity with low energy barrier（0.26 eV）,which originates from the intrinsic activity of Ag₃₈ cluster and the vital role of GDY.（3）The efficient generation of methane by total electroreduction of carbon monoxide（CO）could be of benefit for a more sustainable society.However,a highly efficient and selective catalyst for this process remains to be developed.In this study,density functional theory calculations indicate that steric hindrance in monolayer molybdenum sulfide with 2S vacancies（DV-MoS₂）can facilitate the conversion of CO into CH₄ with high activity and selectivity under electrochemical reduction at a low potential of-0.53V vs.RHE and ambient conditions.The potential is a significant improvement on the state-of-theart Cu electrode（-0.74 V vs.RHE）,with less electrical energy.Moreover,the results suggest that such steric hindrance effects are important for structure-sensitive catalytic reactions.（4）Nitrogen fixation under mild conditions has been one of the most important issues and a long-standing challenge in chemistry.By means of density functional theory calculations,an experimentally available 2D MoC₆ was discovered as a nitrogen reduction reaction（NRR）electrocatalyst.Our results show that MoC₆ with high stability can be prepared experimentally.In particular,MoC₆ exhibits excellent catalytic activity for N₂ fixation at room temperature with a low potential of-0.54 V.The optimal active site,high utilization,selective stabilization of N₂H*species and destabilization of the NH₂*species is responsible for the high activity of MoC₆.Our findings provide a rational strategy for nitrogen activation and ammonia production.