(771e) New Insight Into Reaction Mechanisms of Ethanol Steam Reforming On Co/ZrO2

New Insight into Reaction
Mechanisms of Ethanol Steam Reforming on Co/ZrO₂

Junming Sun^†,‡,
Ayman M. Karim^†, Donghai Mei^†, Mark Engelhard^†,
Yong Wang^{†, ‡ *}

^† Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United
States

^‡ The Gene & Linda Voiland School of Chemical
Engineering and Bioengineering, Washington State University, Pullman Washington
99164, United States

Due to its low
carbon footprint and renewable source, steam reforming of biomass-derived
ethanol (ESR) has been extensively investigated to produce hydrogen for
hydrotreating of biomass derived oxygenates or the potential fuel-cell
application.¹ Among the studied metals, cobalt based catalysts have
been found to be promising in ESR due to its low-cost and high C-C cleavage
activity.^2-4 Previous work has shown that acetone act as mainly intermediate
toward coking.⁵ In this work, a systematic investigation of ESR over
Co/ZrO₂ has been studied using a combination of catalytic evaluation
and characterizations such as X-ray diffraction, nitrogen sorption, in situ
X-ray photoelectron spectroscopy and transmission electron microscopy, as well
as DFT calculations. We show that acetone is a major reaction intermediate
which is steam reformed to selectively form H₂ and CO₂ on
metallic cobalt at 450 °C (Scheme 1, green highlighted path forward). In the
newly discovered sequential reaction pathway, cobalt was found to play a
bifunctional role in transforming ethanol to H₂ and CO₂
with high selectivity. For Co/ZrO₂ catalysts, non-reducible cobalt
(cobalt species strongly interact with ZrO₂ support) passivates most
of the strong acidic sites on ZrO₂, suppresses the undesired dehydration
of ethanol on the support, and favors the dehydrogenation and condensation/ketonization
reaction pathway, resulting in acetone formation. Metallic cobalt (reducible cobalt)
on carbon filament formed during the ESR was found to be mainly responsible for
the subsequent acetone steam reforming reactions.⁶ The current study
not only provides a fundamental new insight into the reaction mechanism of ESR
on Co/ZrO₂, but also sheds a light on how to design high selective
and durable cobalt catalysts for steam reforming of bio-mass derived small
oxygenates (e.g., ethanol, acetone and acetic acid).

Scheme 1 Proposed
main reaction pathway for ethanol steam reforming on Co/ZrO₂
catalysts

Key words: Ethanol
steam reforming, Acetone steam reforming, Cobalt, Hydrogen
production, Reaction mechanism, Nanoparticles

References

         (1)    Cortright, R. D.; Davda, R. R.; Dumesic, J.
A. Nature 2002, 418, 964.

         (2)     Song,
H.; Ozkan, U. S. Journal of Catalysis 2009, 261, 66.

         (3)     Lebarbier,
V. M.; Karim, A. M.; Engelhard, M. H.; Wu, Y.; Xu, B. Q.; Petersen, E. J.;
Datye, A. K.; Wang, Y. ChemSusChem 2011, 4, 1679.

         (4)     Karim,
A. M.; Su, Y.; Sun, J. M.; Yang, C.; Strohm, J. J.; King, D. L.; Wang, Y. Applied
Catalysis B-Environmental 2010, 96, 441.

         (5)     Mattos,
L. V.; Jacobs, G.; Davis, B. H.; Noronha, F. B. Chem. Rev. 2012, 112,
4094.

         (6)     Sun,
J.; Mei, D.; Karim, A. M.; Datye, A. K.; Wang, Y. ChemCatChem 2013,
10.1002/cctc.201300041.