Theoretical Study On The Structural Stability And Catalytic Activity Of Low Dimensional Materials Decorated By Metal At The Atomic Level

The energy issue has become one of the major challenges that the development of human society must confront.The continuous consumption of traditional energy discharges a great deal of harmful gases such as CO,SO₂,H₂S,and NO_x,leading to increasing environmental pollution.Meanwhile,the limited reserves and non-renewable fossil energy will eventually be exhausted.Therefore,researchers pay high attention to the adsorption and conversion of waste gases and clean energy fields such as fuel cells.The realization of these processes cannot be achieved without the participation of catalysts.Au,Ag,Rh,and Pt can effectively adsorb small molecule gases and catalyze CO oxidation and O₂reduction reaction（ORR）in the positive electrode of fuel cell.However,the high cost and low atomic utilization of noble metals limit their application.Single atom catalysts（SACs）and supported cluster catalysts（SMCs）would disperse the active metals at the atomic scale,which can greatly enhance the atomic utilization and catalytic efficiency.Reliable SACs and SMCs require the support of carrier materials with stable structure and properties.In this thesis,a series of SACs and SMCs with high structural stability and catalytic activity were designed using two-dimensional phosphorene,hexagonal boron nitrate（h-BN）and zero-dimensional organic cage CC3 as carriers by first-principles calculations.The main contents are as follows:（1）Two-dimensional phosphorene as carrier material has been investigated.The structural stability and adsorption activity were calculated for a series of supported and embedded SACs formed by metal atoms（Al,Fe,Co,Ni,Cu,Au,Ag,Pt）with phosphorene in CO oxidation reaction,with the embedded Ni/phosphorene being screened out.Ni is stable at the embedded site,Ni/phosphorene can effectively improve the conductivity of phosphorene,and is conducive to the adsorption of O₂and CO as well as the desorption of CO₂,which demonstrate the great potential to catalyze CO oxidation.Langmuir-Hinshelwool（LH）,Eley-Rideal（ER）,Termolecular Eley-Rideal（TER）,and New Eley-Rideal（NER）reaction pathways were compared.The LH mechanism is the most reasonable one,with the activation energy of 0.59 e V in the rate-determining step and the released energy of 4.57 e V in the whole reaction,thus the reaction rate constant of LH is large at room temperature.This study demonstrates that Ni/phosphorene can catalyze CO oxidation efficiently at ambient temperature,providing insights into the design of embedded SACs based on phosphorene.（2）The structure and properties of h-BN are highly similar to graphene,which may serve as the potential support material.By screening the structural stability of different metal atoms supported on h-BN and embedded at B and N sites,it is found that the binding capacity of metal atoms is weak in the supported conditions,and the corresponding metal is more stable when embedded at B site（M/h-BN_B,M=Al,Fe,Co,Ni,Cu,Zn,Au,Ag,Pt）.Meanwhile,Fe/h-BN_Bhas structural advantage and can activate O₂and CO effectively.Four reaction routes have been compared.The LH mechanism is the most favorable one,which possesses the lowest energy barrier of the rate-determining step with the value of 0.52 e V,and the whole process is continuously exothermic.Both of the kinetic and thermodynamic consequences indicate that the CO oxidation would occur at room temperature.It can be predicted that the Fe/h-BN_Bis a good candidate for CO oxidation with high stability and catalytic activity,providing theoretical guidance in the design of new-type h-BN based on non-noble metal SACs.（3）On the basis of above results,the adsorption performances of H₂S,SO₂,NO₂,O₃,N₂O,SO₃,NH₃,CO and NO on non-noble metal M/h-BN_B（M=Fe,Co,Ni,Cu,Zn）were further explored.It is found that Cu/h-BN_B,Zn/h-BN_Bhave appropriate adsorption strength for H₂S and SO₂,O₃and CO,respectively.The conductivity of Cu/h-BN_Band Zn/h-BN_Bcan response to the adsorbed gases.At 298 K,the recovery times of Cu/h-BN_Badsorbed with H₂S and SO₂,and Zn/h-BN_Badsorbed with CO and O₃are 10.68 s,3.93 s,0.14 s and 2.51×10⁴s,respectively.When the temperature rises to 348 K,the recovery time of Zn/h-BN_Badsorbed with O₃decreases to 91.85 s.This indicates that Cu/h-BN_Band Zn/h-BN_Bhave potential application in the field of gas detection,storage and separation,and provides theoretical support for the development of new h-BN based gas adsorption materials.（4）Organic cage CC3 has the potential as new catalyst support due to its intrinsic pore,high dispersibility,and easy recrystallization.To investigate the stability of CC3-type SACs and/or SMCs,typical Ru_xand Cu_x（x=1-19）with CC3were explored.It is found that the diffusion of single Ru or Cu is easy to occur inside of CC3,and the stability of CC3-type SACs is difficult to realize.When x is equal to13,the matching degree between metal clusters and CC3 is optimum,the binding capacity is strong,and the distortion of metal clusters and CC3 is quite small,which is consistent with the experimental results of Ru@CC3.Furthermore,CC3-M₁₃（M=Fe,Rh,Pd,Pt）were compared with CC3-Ru₁₃,CC3-Ru₁₃possesses the most obvious structural superiority and the stronger activation capacity of O₂,which demonstrates the potential for ORR catalyst.The mechanism calculations manifest that the dissociation of O₂is facile on CC3-Ru₁₃,and the continuous protonation of O atom to generate H₂O is favorable under acidic environment.The energy barrier of the rate-determining step is 0.86 e V,and the free energy results also illustrate that the ORR reaction is thermodynamically feasible.This result opens theoretical guarantee for the development and design of CC3 based SMCs with high stability.