Absorption-enhanced reforming of phenol by steam over supported Fe catalysts

Abstract

Supported Fe catalysts of varying support chemical composition prepared by sol-gel and incipient wetness impregnation methods were studied for the steam reforming of phenol (one of the main constituents of tar produced during steam gasification of wood biomass) in the 600-700 °C range. Various natural CO2 absorbent materials were also used together with the supported Fe catalyst in a fixed-bed microreactor to investigate the enhancement of H2 production during short times on stream, as well as the removal of CO2 from the reaction product gas (absorption enhanced reforming [AER]). A 5 wt% Fe/50Mg-50Ce-O catalyst was found to be the most active in terms of H2 product yield, with one of the lowest amounts of accumulated carbonaceous deposits. Among a series of x wt% Fe/50Mg-50Ce-O (x = 1 - 10) catalysts, H2-specific integral production rate (mol-H2/(g s)) goes through a maximum at the 5 wt% Fe loading, whereas the largest amount of "carbon" deposits was measured on the highest Fe-loaded (10 wt%) catalyst. The stability of the 5 wt% Fe/50Mg-50Ce-O catalyst was studied during consecutive oxidation → reaction and oxidation → reduction → reaction cycles of short duration. X-Ray diffraction, X-ray photoelectron spectroscopy, and Mössbauer studies were performed for detailed physicochemical characterization of the supported Fe catalysts in their fresh and used states (after phenol steam reforming). The most active Fe-based catalyst (5 wt% Fe/50Mg-50Ce-O) was found to present a high Fe2+/Fe3+ ratio after phenol steam reforming (Mössbauer studies). Various transient experiments demonstrated that the enhanced production of H2 occurring in the presence of a CO2 absorbent material (supported Fe + CO2 absorbent) for short times on stream was due to a change in the water-gas shift reaction (CO + H2O ↔ CO2 + H2) toward further H2 production. The 5 wt% Fe/Mg-Ce-O catalyst was found to compete favorably with a 35 wt% Ni/γ-Al2O3 industrial catalyst (used for tar steam reforming) at 700 °C in terms of H2 product yield and to have significantly lower CO/CO2 product ratios. © 2006 Elsevier Inc. All rights reserved.