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A Density Functional Theory Study on the Dissociation of H2S, H2O to Hydrogen over Zno SWNTs

Author: SuYan
Tutor: WangJianGuo
School: Zhejiang University of Technology
Course: Industrial Catalysis
Keywords: zinc oxide nanotubes pd nanoclusters H2S splitting water splitting DFT
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 45
Quote: 0
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Abstract


As one kind of wide direct band-gap semiconductor, ZnO has potential applications in several fields. Especially, due to metal oxide nanotube (included ZnO) has the hollow structure and high surface-volume ratio, the active species can distribute on the surface uniformly and locate inside the nanotubes, which leads to novel catalytic properties.We investigated the adhesion of Pd nanoclusters on ZnO (5, 5) and adsorption of probe gas molecules (O2, H2 and CO) on the outside or inside wall of ZnO and Pd1/ZnO SWNTs by means of density functional theory calculations in this study. Our study shows that the binding of Pd clusters on ZnO is mainly via the Pd-O bond interaction. The Pd monomer has the same adhesion ability on both the outside and the inside wall of ZnO SWNTs. However, we found that the adsorption energy of O2 is larger on the inside wall of ZnO and Pd1/ZnO SWNTs than that on the outside one, which is caused by the confinement effect.We further investigated the adsorption and dissociation of H2S on ZnO and ZnO- ZnS SWNTs. It was found that H2S, HS, S, and H preferentially adsorb at the Zn, bridge of Zn- Zn, bridge of Zn-O and O sites, respectively. The potential energy profiles for H2O splitting into H2 and O2 on ZnO-ZnS nanotubes were constructed using the nudged elastic band (NEB) method. The reaction barrier of forming H2O is 40.56 kcal/mol on the clean ZnO SWNTs, while it is 14.45 kcal/mol on the clean ZnO-ZnS SWNTs. The reaction barrier of forming H2 is 88.65 kcal/mol on the clean ZnO SWNTs, which is lower than it is on the clean ZnO-ZnS SWNTs by 4.58 kcal/mol. During the H2O dissociation on Zno-ZnS heterojunction, O2 is formed on the inside wall of nanotubes due to oxygen of H2O is penetrated from outside to inside wall.

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