(192e) In Situ XPS and DRIFTS Studies On the Supported Co/CeO2-ZrO2 Catalysts for Ethanol Steam Reforming

In situ XPS and DRIFTS studies on the
supported Co/CeO₂-ZrO₂ catalysts for ethanol steam
reforming

Sean S.-Y.
Lin,^a Do Heui
Kim,^b and Su Y. Ha,^a,*

^aThe Gene and Linda Voiland School of
Chemical Engineering and Bioengineering,

Washington
State University,

^bInstitute for Interfacial
Catalysis, Pacific Northwest National Laboratory,

The addition of zirconia improves the thermal stability of
ceria as well as its capability of releasing/storing oxygen at the reaction
temperatures for ethanol steam reforming (ESR). These properties allow the use
of cerium-zirconium mixed oxide (CeO₂-ZrO₂) to support
cobalt species for hydrogen production via ESR; the supported cobalt catalyst
(10% Co/CeO₂-ZrO₂) has demonstrated a high hydrogen yield
(4.9 mol H₂/ mol ethanol converted) at 450 ^oC under a
steam-to-carbon (S/C) ratio of 6 by minimizing the production of methane and
carbon monoxide. The maximum hydrogen production rate is 147 mmole/g-s
measured at a WHSV_EtOH of 6.3. However, the catalytic activity and
the selectivity were significantly influenced by the operating S/C ratio. The
dual role of water in ESR was speculated not only to facilitate the
water-gas-shift (WGS) reaction, but also to re-oxidize the pre-reduced cobalt
specie during the reaction. The hydrogen temperature-programmed reduction
(H₂-TPR) study suggested that CoO_x was formed over the
pre-reduced Co/CeO₂-ZrO₂ catalysts when water was
introduced at reforming temperatures.

In this study, in
situ X-ray photoelectron spectroscopy (XPS) was used to investigate the
effect of water and the S/C ratio on the surface composition of
Co/CeO₂-ZrO₂ catalysts in ESR. A series of reduction and
reaction processes for the catalysts were carried out inside the reaction
chamber coupled with XPS. In addition, the surface chemistry of the catalysts
treated under various reduction and reaction conditions was studied by an in situ diffuse-reflectance infrared
Fourier transform spectroscopy (DRIFTS) in order to explore the water-ethanol
interactions over the catalyst surfaces and its effect on the catalytic
selectivity.