A First-principles Study On NO Heterogeneous Absorption On Carbon Surface And The Effects Of Defect,Metal And Functional Groups

Since the nitric oxide?NO?absorption on carbon surface is of significance in NO_x reduction,its reaction mechanism and the effects of surface defect,metal and surface functional groups on the reduction reaction were studied using first-principles computation.Three-dimension periodic boundary condition graphene surface was adopted to simulate the practical carbon surface,such as char and active carbon.Mono-vacancy defect graphene was used when considering the catalytic effect of surface defect on carbonaceous material surface.The metal decoration on graphene surface was first introduced to explain the catalytic effect of calcium and potassium whose coverage were 13.3 % and 13.0 %,respectively.In order to study the influence of oxygen-containing functionalities and nitrogen-containing functionalities,four typical types were used in computation: doped oxygen,carbonyl,doped nitrogen and amine.In terms of carbonyl and amine,the effect of the distance between them and the graphene surface on NO absorption was investigated.It is found that the absorption of NO molecule on pristine graphene surface was physic-sorption with the binding energy-19.34 kJ/mol.However,when NO cluster absorbed,it turned to chemisorption because of the van der Waals interaction among molecules.Surface defect and metal demonstrated satisfactory catalytic effect on NO absorption on graphene surface.When defect appeared on graphene surface,the binding energy of molecule absorption was as high as-528.09 kJ/mol.Despite the binding energy of cluster absorption suffered a bit decrease,the absorption was still chemisorption.With regard to graphene doped with Ca atom and K atom which attracted the NO molecule,its binding energy with NO molecule increased dramatically by-206.02 kJ/mol and-307.08 kJ/mol,respectively.The binding energy dropped substantially,but the catalytic effect of two metal was still obvious.However,the influence of functionalities on NO absorption was quite complex.The doped oxygen could generate stable structure with NO molecule through chemisorption,while carbonyl grafted onto the graphene surface could oxidize NO to NO₂.The doped nitrogen exerted little influence on NO absorption,while the amine grafted onto the graphene surface reacted with NO and generated H₂NNO?nitrosamide?which was a stable intermediate and would desorbed from graphene surface.But theeffect of carbonyl and amine on NO absorption was undermined when they stayed away from the graphene surface.The results in this dissertation is meaningful when used in upgrading low NO_x emission control technologies and developing ambient temperature NO solid absorbent.