1. Effects of structure and size of Ni nanocatalysts on hydrogen selectivity via water-gas-shift reaction—A first-principles-based kinetic study.
- Author
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Zhou, Mingxia, Le, Thong Nguyen-Minh, Huynh, Lam K., and Liu, Bin
- Subjects
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HYDROGEN production , *HYDROGEN analysis , *WATER gas shift reactions , *DENSITY functional theory , *METHANATION - Abstract
The effects of structure and size of nickel nanocatalysts on hydrogen production via water-gas shift reaction (WGSR) were investigated using a first-principles-based kinetic model. Using periodic density functional theory and statistical calculations, thermochemistry and kinetics of the WGSR and competing methanation was calculated on Ni(111), Ni(100), and Ni(211) facets. The kinetics of the elementary reactions involving C H, O H, and C O bond was found to fit to a general Brønsted–Evans–Polanyi (BEP) type linear relationship on all Ni facets considered. A mechanism describing the competition between the hydrogen and methane formation routes is constructed for further microkinetic modeling. The hydrogen production turnover frequency (TOF) via the WGSR route suggests the preference to the low-coordinated surface sites with the reaction activities following the order of Ni(211) > Ni(100) > Ni(111) using a simulated feed gas with a molar ratio of CO:H 2 O = 1:2. Due to the methanation, the TOF of methane production follows the same trend of hydrogen production. Consequently, the TOF of hydrogen production decreases with increasing particle diameters, due to the decreasing fractions of low-coordinated surface nickel atoms. It is also found that the presence of H 2 in feed gas can largely enhance the methanation reaction. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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