Photoacoustic measurements of water-gas shift reaction on ferric oxide catalyst

A photoacoustic spectroscopic (PAS) technique was applied to the kinetic study of the water-gas shift reaction in the presence of α-Fe₂O₃ catalyst. The catalytic reaction was performed in the temperature range from 523 to 673 K at various partial pressures of carbon monoxide and water-vapor in a closed-circulation reactor system using a differential photoacoustic cell. The variation of CO₂ photoacoustic signal with the concentration of CO₂ produced during the reaction was recorded as a function of time. The time-resolved photoacoustic spectra obtained for the early reaction stage provided precise data of CO₂ formation rate. The results of CO₂ photoacoustic spectra indicated that the catalytic water-gas shift reaction over α-Fe₂O₃ occurred when α-Fe₂O₃ was partially reduced to Fe₃O₄ by heating it in vacuum. The vacuum-pretreated α-Fe₂O₃ catalyst showed catalytic activity for the water-gas shift reaction and its rate of CO₂ formation increased with increasing temperature in this temperature range. The rate of CO₂formation on the vacuum-activated α-Fe₂O₃ catalyst was highly enhanced when the catalyst was treated in situ with H₂O(g) prior to the admittance of CO(g)/H₂O(g) reaction mixture. The reaction orders determined from the initial reaction rates of CO₂ formation were found to be 0.80 and 0.08 with respect to CO and H₂O, respectively. From the experimental results, the active sites and the reaction mechanism for the water-gas shift reaction on the vacuum-activated α-Fe₂O₃ catalyst could also be discussed.