PNNL

Abstract

The effect of Zn promotion on the activity and selectivity of Co/ZrO2 catalysts for ethanol steam reforming was investigated. The catalysts were synthesized by incipient wetness impregnation and characterized using BET measurements, temperature programmed reduction, X-ray diffraction, transmission electron microscopy, and X-ray electron spectroscopy. Compared to Co/ZrO2 catalyst, a higher ethanol conversion and a lower CH4 selectivity were observed for the Co/ZrO2 catalyst promoted with Zn. It was found that addition of Zn inhibits the oxidation of metallic cobalt (Co0) particles, which results in a higher ratio of Co0/Co2+ present in the Zn promoted Co/ZrO2 catalyst. These results suggest that metallic cobalt (Co0) is responsible for ethanol conversion via ethanol dehydrogenation whereas Co2+ plays a role in the CH4 formation. For both catalysts, the experimental results show that CH4 is mainly produced via CO and/or CO2 methanation. TPR measurements, on the other hand, show Zn addition inhibits the reduction of Co2+ and Co3+, which would mislead the conclusion that oxidized Co is required to reduce the CH4 formation. Therefore, TPR may not be appropriate to correlate the degree of metal reducibility (in this case Co0) with the catalyst activity for reactions such as ethanol steam reforming where oxidizing conditions exist.