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The Effect of Zinc Addition on the Oxidation State of Cobalt in Co/ZrO 2 Catalysts
Author(s) -
Lebarbier Vanessa M.,
Karim Ayman M.,
Engelhard Mark H.,
Wu Yu,
Xu BoQing,
Petersen Eric J.,
Datye Abhaya K.,
Wang Yong
Publication year - 2011
Publication title -
chemsuschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.412
H-Index - 157
eISSN - 1864-564X
pISSN - 1864-5631
DOI - 10.1002/cssc.201100240
Subject(s) - cobalt , catalysis , zinc , oxidation state , inorganic chemistry , chemistry , materials science , chemical engineering , organic chemistry , engineering
The effect of zinc promotion on the oxidation state of cobalt in Co/ZrO 2 catalysts was investigated and correlated with the activity and selectivity for ethanol steam reforming (ESR). Catalysts were synthesized by applying incipient wetness impregnation and characterized by using Brunauer–Emmett–Teller (BET), temperature‐programmed reduction (TPR) measurements, X‐ray diffraction (XRD), transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS). Higher ethanol conversion and lower CH 4 selectivity are observed for the Co/ZrO 2 catalyst promoted with Zn as compared to the Co/ZrO 2 catalyst alone. Addition of Zn inhibits the oxidation of metallic cobalt (Co 0 ) particles and results in a higher ratio of Co 0 /Co 2+ in the Zn‐promoted Co/ZrO 2 catalyst. These results suggest that metallic cobalt (Co 0 ) is more active than Co 2+ in the ethanol conversion through dehydrogenation and that Co 2+ may play a role in the CH 4 formation. TPR measurements, on the other hand, reveal that Zn addition inhibits the reduction of Co 2+ and Co 3+ , which would lead to the false conclusion that oxidized Co is required to reduce the CH 4 formation. Therefore, TPR measurements may not be appropriate to correlate the degree of metal reducibility (in this case Co 0 ) with the catalyst activity for reactions, such as ESR, where oxidizing conditions exist.