Metallic phases of cobalt-based catalysts in ethanol steam reforming: The effect of cerium oxide

The catalytic activity of cobalt in the production of hydrogen via ethanol steam reforming has been investigated in its relation to the crystalline structure of metallic cobalt. At a reaction temperature of 350 degrees C, the specific hydrogen production rates show that hexagonal close-packed (hcp) cobalt possesses higher activity than face-centered cubic (fcc) cobalt. However, at typical reaction temperatures (400-500 degrees C) for ethanol steam reforming, hcp cobalt is transformed to less active fcc cobalt, as confirmed by in situ X-ray diffractometry (XRD). The addition of CeO2 promoter (10 wt.%) stabilizes the hcp cobalt structure at reforming temperatures up to 600 degrees C. Moreover. during the pre-reduction process, CeO2 promoter prevents sintering during the transformation Of Co3O4 to hcp cobalt. Both reforming experiments and in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that the surface reactions were modified by CeO2 promoter on 10% Ce-Co (hcp) to give a lower CO selectivity and a higher H-2 yield as compared with the unpromoted hcp Co. (C) 2008 Elsevier B.V. All rights reserved.