COMPARISON OF THE DYNAMICS OF THE HIGH-TEMPERATURE WATER-GAS SHIFT REACTION ON OXIDE CATALYSTS

The dynamics of the high-temperature water-gas shift reaction on iron oxide and Co-Mo-oxide catalysts was studied with transient response ex periments performed at 563-673 K at atmospheric pressure in a gradient less spinning basket reactor. At the reaction start-up the step respon se of CO2 on the iron oxide catalyst was always faster than the respon se of H2, whereas the response of H2 on the Co-Mo catalyst was faster than the response of CO2. Water pretreatment retarded the response of H2 on the iron oxide catalyst, whereas a similar pretreatment accelera ted the response of H2 on the Co-Mo catalyst. Based on the results of the transient response experiments reaction mechanisms were proposed f or the water-gas shift reaction on both catalysts. The rate determinin g steps on the iron oxide catalyst were assumed to be the CO2 desorpti on and surface hydroxyl decomposition steps. The rate determining step s on the Co-Mo catalyst were assumed to be the surface reaction and CO 2 desorption steps. The transient responses were modelled with non-ste ady-state rate equations based on the mechanisms, and the kinetic cons tants were determined by regression analysis. The kinetic models were able to describe the transient behaviours of the oxide catalysts.