Thermochemistry of Elementary Reactions in Water–Gas Shift Reaction on Ni(111): An Ab Initio Study

Abstract

A comprehensive thermodynamic study of the water–gas shift (WGS) reaction was performed using density functional theory (DFT). Chemisorption involves the formation of new chemical bonds between adsorbed species and atoms of the substrate. Adsorbates dissociate on the metal surface because of weaker intermolecular bonds on the surface. The adsorption energies of 12 adsorbed species were calculated on Ni(111) surface. Moreover, 21 elementary reactions were considered for investigating the mechanism of water–gas shift (WGS) reaction on Ni(111). A detailed thermodynamic calculation of the WGS reaction is shown and discussed in this work. The vibrational frequencies were calculated for all the gaseous species, top surface layer atoms, and adsorbed configurations. Thermochemistry of the surface reactions was calculated using spin-paired DFT with RPBE functional for exchange and correlation. This report covers the adsorption energies, vibrational frequencies, and thermochemistry of chemical species such as H2, H2O, CO and CO2, involved in the WGS reaction, on the Ni(111) surface. Vibrational calculations were performed only on their favorable sites. Finally, the thermochemistry ([Formula: see text]E, [Formula: see text]H, [Formula: see text]S, [Formula: see text]G) of elementary reactions was calculated, and thermodynamically driven reaction mechanisms were determined for the water–gas shift reaction on Ni(111) surface. We found that thermodynamically predicted mechanisms are in good accord with the kinetic predictions and can be considered a good first approximation.

Keywords

• Water-gas shift reaction
• Ni(111)
• thermochemistry
• catalytic reactions