The Effect of Carbon Monoxide Co-Adsorption on Ni-Catalysed Water Dissociation

Abas Mohsenzadeh,Tobias Richards,Anders Borjesson,Jeng-Han Wang,Kim Bolton

doi:10.3390/ijms141223301

Abas Mohsenzadeh, Tobias Richards + Show 3 more

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https://doi.org/10.3390/ijms141223301

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Abstract

The effect of carbon monoxide (CO) co-adsorption on the dissociation of water on the Ni(111) surface has been studied using density functional theory. The structures of the adsorbed water molecule and of the transition state are changed by the presence of the CO molecule. The water O–H bond that is closest to the CO is lengthened compared to the structure in the absence of the CO, and the breaking O–H bond in the transition state structure has a larger imaginary frequency in the presence of CO. In addition, the distances between the Ni surface and H2O reactant and OH and H products decrease in the presence of the CO. The changes in structures and vibrational frequencies lead to a reaction energy that is 0.17 eV less exothermic in the presence of the CO, and an activation barrier that is 0.12 eV larger in the presence of the CO. At 463 K the water dissociation rate constant is an order of magnitude smaller in the presence of the CO. This reveals that far fewer water molecules will dissociate in the presence of CO under reaction conditions that are typical for the water-gas-shift reaction.

Highlights

The water gas shift (WGS) reaction, carbon monoxide (CO) + H2O → CO2 + H2, is important in many industrial processes, including methanol synthesis and production of hydrogen for use in, e.g., fuel cells
The efficiency of the WGS reaction is enhanced in the presence of transition metal catalysts such as nickel, which is widely used due to its high heat conductivity, high catalytic conversion and its capability to be manufactured in different shapes [6,7,8,9]
The results show that the co-adsorption of CO alters the geometry of the adsorbed reactant water molecule

Summary

Introduction

The water gas shift (WGS) reaction, CO + H2O → CO2 + H2, is important in many industrial processes, including methanol synthesis and production of hydrogen for use in, e.g., fuel cells. It is one of the most important reactions in gasification, where carbonaceous materials are converted to a gaseous product that can be used to produce energy or other desirable chemicals [1,2,3,4,5]. Shekhar et al have investigated the promotional effect of alkali additives (Na, Li and K) on the WGS reaction for Pt/Al2O3 and Pt/TiO2 catalysts They showed that the active platinum remains in the metallic state and that the promotion by alkali is due the modification of the support properties [12]. Cordeiro et al studied the role of the step sites in the WGS reaction catalyzed by Cu and found that the associative route through the carboxyl intermediate assisted by co-adsorbed OH is favored in the presence of steps [14]

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