The Kinetics of the Water-Gas Shift Reaction on Nickel(II) Oxide Catalysts in the Néel Temperature Region

The water-gas shift reaction has been studied from 200 to 300 °C at atmospheric pressure on both black and green forms of nickel(II) oxide which contrast in their magnetic properties and stoichiometry. Whereas black oxide samples, prepared in various ways, exhibited activation energies of 23 ± 1 kcal mol −1 throughout the temperature interval, the green oxides were characterized by a change in activation energy from 20 ± 1 kcal mol −1 above 250 °C to between 10 and 15 kcal mol −1 below this temperature. These values were obtained with a standard water-gas mixture of 40 Torr carbon monoxide and 40 Torr water vapor. With a carbon monoxide partial pressure of 80 Torr the green oxide gave a monotonic value of 21 ± 1 kcal mol −1 .Rate order data suggest that the rate-limiting process does not change on the black oxides in this temperature interval, whereas on the green oxides rate control is probably associated with the surface reactivity of carbon monoxide above 250 °C and water vapour below this temperature. These effects may be related to different forms of active surface oxygen species that are present on the green oxide samples above and below the Néel temperature region.