Steam reforming of biomass tar model compound at relatively low steam-to-carbon condition over CaO-doped nickel–iron alloy supported over iron–alumina catalysts

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CaO doped iron–alumina-supported nickel–iron alloy catalysts were tested in a fixed-bed reactor for steam reforming of toluene as a biomass tar model compound at a relatively low steam-to-carbon (S/C) ratio of 2. The influence of doping CaO to iron–alumina support was also explored for the steam reforming reaction. Ni supported on a CaO(1.5)–Fe2O3–Al2O3 support (Ni/Ca(1.5)–Fe–Al) gave superior catalytic performance in terms of activity and stability over other catalysts. Ni/Ca(1.5)–Fe–Al gave a toluene conversion of more than 80% for a period of 22h testing at a S/C ratio of 2. XRD analysis showed that the Ni–Fe alloys formed were stable throughout the reforming reaction. It was observed from XPS results that the surface of the reduced Ni/Ca(1.5)–Fe–Al catalyst was enriched with Fe species compared to other catalysts. These enriched surface Fe species play the role of co-catalysts by increasing the coverage of oxygen species during the reforming reaction to enhance the reaction of toluene and to suppress coke formation. The temperature-programmed surface reaction (TPSR) with water reveals that the Ni/Ca(1.5)–Fe–Al catalyst can activate water molecule at relatively lower temperature over other CaO doped catalysts. TGA analysis on spent catalysts reveals that all CaO-containing catalysts generally result in lower carbon formation rates as compared to Ni/Fe–Al catalyst.