Water-gas shift reaction (WGSR) plays a significant role in industrial catalytic hydrogen production. Ni catalyst is an efficient and economical catalyst for WGSR, while it can also catalyze methanation that lowers hydrogen selectivity. First-principles study and micro-kinetic modeling have been performed to investigate the reaction mechanisms to elucidate selectivities of hydrogen production on Ni(111), Ni(211) and Ni(100) surfaces. By understanding the fundamental mechanism that governs the catalytic behavior, we can evaluate and predict the catalytic performance (e.g. bimetallic system, promoter effect) to achieve rational catalyst design. Three WGSR reaction pathways include redox pathway (CO* + O* →CO2 (g)), carboxyl pathway (CO* + OH* →COOH* →CO2 (g) +H*) and formate pathway (CO*+ H* +O* → CHO* + O* →HCOO* →CO2 (g) + H*) and five methanation pathways corresponding to C-O bond cleavage from different intermediates (e.g. CO*, COH*, CHO*, HCOH* and CH2OH*) are considered on Ni model surfaces. Detailed DFT modelings indicate that the redox pathway, carboxyl pathway and CHO pathway (CO* + H* →CHO* →CH*+O*) are the most favorable pathways for WGSR and methanation on Ni(111), respectively. Comparisons of energetics on different active surfaces, redox pathways decrease in the order of Ni(100) &gt; Ni(211) ~ Ni(111), while the energetics of carboxyl pathways decrease in order of Ni(211) &gt; Ni(111) &gt; Ni(100). For CHO pathways, their energetics decreases in order of Ni(211) &gt; Ni(100) &gt; Ni(111). To generalize the catalytic properties, a volcano plot was generated, which shows gas CO2 production rate decreases in order of Ni(211) &gt; Ni(100) &gt; Ni(111). Our thermodynamic and kinetic analyses on different active sites generate valuable insights for the design to improve WGSR catalysts with higher H2 selectivity and lower cost.

Thermodynamic and kinetic investigation on the selectivity of water-gas shift reaction on Ni catalyst

251st National Meeting (2016)

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