Hydrogen production by steam reforming of ethanol over nickel supported on La-modified alumina catalysts prepared by sol–gel

Abstract

The catalytic properties for steam reforming of ethanol (SRE) of 10wt.% nickel supported on La-modified alumina prepared by sol–gel were studied. Lanthanum oxide content was in the range 0–12wt.%. Supports were calcined at 650°C and catalysts were calcined at 450°C and reduced at 600°C. Catalysts were characterized by ICP, XRD, TPR, TPO and TEM. The progressive La-addition to the support had several effects: a structural effect in the alumina, promotion of a better dispersion of the NiO phase and increased number of NiO species reducing at lower temperature. Average Ni crystal size as determined by XRD in reduced samples was 6.3nm. The SRE at molar ratio H2O/EtOH=3 was studied and ethanol conversion as a function of temperature showed small differences as a function of the lanthanum content, but the hydrogen yield was much more important for La-containing catalysts. Deactivation experiments at 500°C showed that catalysts with higher La content were more stable and that the strong decrease in the ethanol conversion occurred in the first hours on stream at these experimental conditions. A good correlation between deactivation trend, ethylene evolution and occurrence of lower temperature gasified carbon-type residues was established with the support composition. Sintering of Ni particles occurred in all samples after reaction, but despite the presence of larger Ni particles in the Ni/Al2O3–La12 catalyst this was the most stable one. As lanthanum species are progressively present in the support its contribution to stabilization of the catalyst is certainly related to the enhancement of gasification of carbon residues on the surface of the catalyst but also to a close interaction with nickel particles.