Ethanol steam reforming over Rh/CexZr1−xO2 catalysts: Impact of the CO–CO2–CH4 interconversion reactions on the H2 production

CexZr1−xO2 mixed oxide-supported 1 wt.%Rh catalysts were prepared by wet impregnation using Rh nitrate as a precursor and calcined at 900 °C. They were characterized by BET surface area, XRD, CO2 chemisorption and H2 chemisorption at −85 °C and tested in the ethanol steam reforming at 600 °C under atmospheric pressure, with water to ethanol molar ratio equal to 4, without carrier gas. The best performances, i.e. the highest hydrogen yield and the lowest coke deposition, were obtained over Rh/Ce0.5Zr0.5O2, i.e. 3.63 mol H2/molethanol. This catalyst was subsequently evaluated under various reaction conditions. Whatever the temperature and the water to ethanol ratio, the ethanol steam reforming yielded a large amount of methane, which tends to reduce the H2 production. To elucidate the origin of the methane production, CO/CO2/CH4 interconversion reactions were studied. It was shown that such catalyst favours the formation of methane via CO hydrogenation. The direct hydrogenation of CO2 was not observed. In parallel, the catalyst was active in the reverse water gas shift (RWGS) reaction between CO2 and H2, leading CO and H2O.