Origin and nature of coke in ethanol steam reforming and its role in deactivation of Ni/La2O3-αAl2O3 catalyst

Abstract

Deactivation of Ni/La2O3-αAl2O3 catalyst in the ethanol steam reforming (ESR) was studied in order to establish the optimal conditions for maximizing H2 production and achieving a steady behaviour. The ESR reactions were conducted in a fluidized bed reactor under the following operating conditions: 500-650 ºC; space-time up to 0.35 gcatalysth/gEtOH; and steam/ethanol (S/E) molar ratio in the feed, 3-9. The features of the deactivated catalysts, and the nature and morphology of the coke deposited were analysed by Temperature Programmed Oxidation, X-Ray Diffraction, Scanning Electron Microscopy, and Raman Spectroscopy. Catalyst deactivation was solely caused by coke deposition, especially by encapsulating coke, with acetaldehyde, ethylene and ethanol being the main precursors, whose concentration was high for lower values of space-time. Conversely, the filamentous coke formed from CH4 and CO (with their highest concentration for intermediate values of space-time) had a much lower impact on deactivation. Owing to the effect of space-time on the extent of reactions leading to the formation of coke precursors, the Ni/La2O3-αAl2O3 catalyst stability was enhanced by increasing space-time. The increase in temperature and S/E ratio was also beneficial, since both variables promoted coke gasification. Consequently, a steady H2 yield throughout 200 h reaction was attained at 600 ºC, space-time of 0.35 gcatalysth/gEtOH and S/E > 3.