Comparison of the dynamics of the high-temperature water-gas shift reaction on oxide catalysts

Abstract

The dynamics of the high-temperature water-gas shift reaction on iron oxide and Co-Mo-oxide catalysts was studied with transient response experiments performed at 563–673 K at atmospheric pressure in a gradientless spinning basket reactor. At the reaction start-up the step response of CO 2 on the iron oxide catalyst was always faster than the response of H 2, whereas the response of H 2 on the Co-Mo catalyst was faster than the response of CO 2. Water pretreatment retarded the response of H 2 on the iron oxide catalyst, whereas a similar pretreatment accelerated the response of H 2 on the Co-Mo catalyst. Based on the results of the transient response experiments reaction mechanisms were proposed for the water-gas shift reaction on both catalysts. The rate determining steps on the iron oxide catalyst were assumed to be the CO 2 desorption and surface hydroxyl decomposition steps. The rate determining steps on the Co-Mo catalyst were assumed to be the surface reaction and CO 2 desorption steps. The transient responses were modelled with non-steady-state rate equations based on the mechanisms, and the kinetic constants were determined by regression analysis. The kinetic models were able to describe the transient behaviours of the oxide catalysts.