Ammonia synthesis by Nitrogen and Hydrogen on W(111)surface:A Computational Study

• Main Authors: LI, Guan-Ying, 李冠穎
• Other Authors: Chen, Hui-Lung
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/82272301950536669796

碩士 === 中國文化大學 === 化學系應用化學碩士班 === 103 === In our studies, we employed Vienna Ab intio Simulation Package (VASP) to calculate the N2 adsorption and hydrogenation on W(111) surface. The calculated results show that the possible coordinates of three isomers for the N2 adsorption on W(111) are WN2(T-η1-N), WN2(T,S-μ2-N,N) and WN2(T,T-μ2-N,N), respectively. Among them, the most stable structure is WN2(T,T-μ2-N,N) with the adsorption energy of -22.44 kcal/mol. For the first hydrogenation process, we consider two possible pathways: the first one is the direct dissociation of N2 before the hydrogenation, the second one is the hydrogenation of N2 before its dissociation. Our calculated results show that the reaction will favor the second pathway. In the second hydrogenation process, it is found that the formation of HNNH fragment will possess the lowest activation barrier. However, the lower activation barrier of N-N bond scission of N2H2 is also observed in our calculation. Based on the energy point of view, we could conclude that the HNNH would dissociate to two NH fragments. Finally, we also study Electron Localization Function (ELF) of W(111) surface, and the results can explain our predicted orientations of favorable adsorption structures. To gain more insights into catalytic processes of the aforementioned conducts, the interaction nature between the adsorbate and substrate is analyzed via detailed electronic analysis.