Photoacoustic measurements of water–gas shift reaction on ferric oxide catalyst Original Research Article

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 CO2 formation 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.