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.