Theoretical Study Of Co Oxidation Mechanism On MnN4-CNT And Ti/SnO₂ Single Atom Catalysts

The human beings are facing many serious problems,which were caused by the excessivepopulation growth,such as energy crisis and environmental pollutions.Scientists are paying more attiention to the design of the highly efficient catalyst materials to resolve the pollutants.Carbon monoxide?CO?is one of the major air pollutants,so it is significant for us to use efficient catalysts to remove CO from industrial productions or automobile exhausts.According to the previous theoretical studies,the smaller size of the nanoparticles with a larger surface free energy.And the single atom catalysts have attracted people's great interests,as the single atom catalysts exhibit many promising properties,such as the large surface free energy,unsaturated coordination environment,quantum size effect and the interaction between metal substrates.These properties of the single atom catalysts enhance their excellent catalytic performances.Compared with the traditional precious metal catalysts,every metal atom in the single atom catalysts can be used as active site,which can result in"less do more"for their catalytic efficiency.In this article,the first principles method based on density functional theory was carried out on the two single atom catalysts for the CO oxidation reaction mechanisms.The first model is Mn-N4 porphyrin-like carbon nanotube?MnN4-CNT?,and the second model is Ti-doped SnO₂?110?surface?Ti/SnO₂?110??.The main results are as follows:1)All calculations of CO oxidation on MnN4-CNT substrates are based on density functional theory including dispersion corrections?DFT-D?.The results of the molecular dynamic simulations exhibit that the MnN4-CNT is very stable,and we found that the CO and O₂ molecules tend to be anchored at the top of the MnN4 center,and the adsorption of CO is slightly stronger than O₂.The CO oxidation reaction mechanisms on Mn N4-CNT was explored by three mechanisms:Eley-Rideal?ER?mechanism,Langmuir-Hinshelwood mechanism?LH?and a new type of three molecules Eley-Rideal?TER?mechanism.The TER reaction mechanism is the most preferable,according to the comparision with their energy barrier of the rate-limit step,indicating that MnN4-CNT is a promising catalyst to CO oxidation at room temperature.2)The CO oxidation on Ti/SnO₂?110?surface has been systematically studied by using the first-principles calculations within the density functional theory.We found that the most preferable doping position of Ti is the 6-fold Sn atom at the top layer.The lattice oxygen of bridge site easily reacts with CO to transforming into CO₂ on the Ti/SnO₂?110?surface.The results indicate that the formation of bridge site oxygen vacancies are energetically easy and improve sensitivity of sensor for the following CO oxidation.Besides,the two favorable pathways of CO oxidation on the surface occurs with a small reaction barrier of0.67 eV and 0.83 eV,respectively.These results suggest that the Ti-doping can improve the gas sensing properties of the Sn O₂-based sensors for CO gas.