(197d) Investigation of Cobalt Coordination Environment Under in-Situ Steam Reforming Conditions of Bio-Derivable Liquids

I. Ilgaz Soykal, Hyuntae Sohn, Umit S. Ozkan, The Ohio State University, Columbus, USA

Overview

Hydrogen is considered to be a major candidate for future energy carriers with its high gravimetric energy density and a potential to be the fuel for the fuel cells. However, difficulties associated with its transportation have funneled the research effort in working with intermediate substances with high molecular hydrogen to carbon yields. Bio-derived liquids such as dimethy-ether, ethanol and acetaldehyde are more suitable to transport with the pre-existing infrastructure, and may lend themselves well to a distributed hydrogen generation strategy. Use of bio-derived liquids as the hydrogen source also has the potential to provide clean energy with a minimal carbon footprint.

Cobalt-based catalysts supported on high surface area oxides such as ceria have shown promising activity and are significantly less expensive than the traditional noble metal based catalysts such as rhodium. Our previous work has shown promising hydrogen yields with the product stream being highly selective to CO₂ in the temperature range of 350-500 ˚C[1-3].  The work has also shown the importance of the surface acidity and oxygen mobility of the support. Our more recent work also examined the coordination environment of Co species under reaction conditions[4].

Effect of support morphology on Co oxidation state

It has been observed that tailoring the morphology of the support affects the steam reforming activity of ethanol and acetaldehyde through increasing oxygen mobility and favoring different ceria crystal planes with different affinities for supporting anion vacancies. Ceria nanorods (NR) and nanocubes (NC) are synthesized with average particle sizes of 20x6 nm and 23x23 nm, respectively, as shown by high-resolution TEM images. Cobalt catalysts supported on these nano-rods and nano-cubes are seen to exhibit significant differences in dispersion, reducibility and catalytic performance, as shown through X-ray diffraction, in-situ EXAFS, thermogravimetry and calorimetry studies as well as steady-state reaction experiments. The catalysts are further characterized via a wide array of techniques using X-ray photoelectron spectroscopy, post-reaction transmission electron microscopy and temperature programmed techniques, as well as in-situ and operando spectroscopy techniques including laser Raman spectroscopy and diffuse reflectance Fourier transform infrared spectroscopy.

[1]          H. Song, U.S. Ozkan, J. Phys. Chem. A 114 (2010) 3796-3801.

[2]          H. Song, U.S. Ozkan, J. Catal. 261 (2009) 66-74.

[3]          H. Song, U.S. Ozkan, J. Mol. Cat. A 318 (2010) 21-29.

[4]          B. Bayram, I.I. Soykal, D. von Deak, J.T. Miller, U.S. Ozkan, J. Catal. 284 (2011) 77-89.