Catalytic steam reforming of bio-oils for the production of hydrogen: effects of catalyst composition

Catalytic steam reforming of condensable vapors (i.e. bio-oils) derived fro m pyrolysis of biomass is a technically viable process for hydrogen product ion. In this study the aqueous fraction of bio-oil, generated from fast pyr olysis, was catalytically steam reformed at 825 and 875 degrees C, high spa ce velocity (up to 126,000 h(-1)) and low residence time (26 ms). Using a f ixed-bed micro-reactor interfaced with a molecular beam mass spectrometer ( MBMS), a variety of research and commercial nickel-based catalysts were tes ted. The catalysts were prepared by impregnation of an alpha-Al2O3 support with nickel and additives. Since the main constraint in reforming bio-oils is catalyst deactivation caused by carbon deposition, two strategies were a pplied to improve the performance of the catalysts. The first approach aime d at enhancing steam adsorption to facilitate the partial oxidation, i.e. g asification of coke precursors. The second one attempted to slow down the s urface reactions leading to the formation of the coke precursors due to cra cking, deoxygenation, and dehydration of adsorbed intermediates. Magnesium and lanthanum were used as support modifiers to enhance steam adsorption wh ile cobalt and chromium additives were applied to reduce coke formation rea ctions. The cobalt-promoted nickel and chromium-promoted nickel supported o n MgO-La2O3-alpha-Al2O3 catalysts showed the best results in the laboratory tests. At the reaction conditions progressive catalyst deactivation was ob served leading to a decrease in the yields of hydrogen and carbon dioxide a nd an increase in carbon monoxide. The loss of activity also resulted in th e formation of higher amounts of methane, benzene and other aromatic compou nds. Commercial catalysts that were developed for steam reforming of natura l gas and crude oil fractions proved to be more efficient for hydrogen prod uction from bio-oil than most of the research catalysts mainly due to the h igher water-gas shift activity. (C) 2000 Elsevier Science B.V. All rights r eserved.