Steam reforming of ethanol on supported nickel catalysts

The catalytic behavior of Ni/Al2O3 catalysts modified with La and Ag was investigated in the steam reforming of ethanol. The catalysts were characterized by SBET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and Fourier transform infrared spectroscopy (FTIR) of CO adsorption. The reaction rate for noncatalytic decomposition of ethanol in the homogeneous gas phase becomes significant only at high temperatures (T >= 890 K). FTIR results revealed that Ag strongly modifies the Ni surface, decreasing the intensity ratio of the bands for adsorbed CO in the bridging mode at low frequency (LF) and the linear mode at high frequency (HF). Similar but smaller effect was observed in the Lacontaining catalyst. The activity and stability against carbon depostion for steam reforming of ethanol of Ni/Al2O3 catalyst was only slightly sensitive to Ag but the activity was strongly dependent on the presence of La. The reaction data suggest that at temperatures lower than 650 K the Ni/Al2O3 catalyst was active for decomposition of ethanol via the acetaldehyde intermediate, showing high selectivity to methane and CO. The rate of steam reforming of ethanol became significant at temperature higher than 650 K. Comparing Ni/Al2O3 and Ni/La-Al2O3 catalysts the results pointed out that the Ni became more susceptible to modification by water in La-containing Ni catalyst. The Ni/La-Al2O3 catalysts become inactive at low temperatures, and the activity could be regenerated with reduction of NiO by ethanol on raising the reaction temperature. Differently front the steam reforming of methane, the coking cannot be suppressed by Ag promotion in the case of steam reforming of ethanol. Inversely, the La has a positive effect to decreasing coking on Ni catalysts. A scheme for ethanol reactions with H2O on Ni surfaces is proposed based on reaction tests. (c) 2007 Elsevier B.V. All rights reserved.