Comparative study on steam reforming of model aromatic compounds of biomass tar over Ni and Ni–Fe alloy nanoparticles

Steam reforming of tar model compounds (benzene, toluene and phenol) was carried out using Ni–Fe/Mg/Al catalysts prepared by calcination and reduction of hydrotalcite-like precursor. Ni–Fe/Mg/Al (Fe/Ni = 0.25) catalyst showed higher activity (∼twice conversion rate based on catalyst weight) and better resistence to carbon deposition (∼one order smaller amount of deposited carbon) than Ni/Mg/Al. The difference in the weight-based rate and carbon deposition amount between catalysts with and without Fe was large when benzene or toluene was used as a substrate and high steam/carbon (S/C) ratio was applied. On the other hand, when phenol was used as a substrate, relatively large amount of carbon derived from decomposition of phenol was deposited on Ni–Fe/Mg/Al catalyst even with high (3.8) S/C ratio. The catalyst loses some activity for steam reforming of toluene when treated with phenol (untreated catalyst: ∼80% conversion of toluene (rate 51 μmol g−1-cat s−1); treated catalyst ∼60% (rate 38 μmol g−1-cat s−1)), probably because of the deposited carbon from phenol. Kinetic studies and O2- or H2O-TPO studies showed that phenol was strongly adsorbed on Fe site as well as Ni site, and the adsorbed phenol could be converted into carbonaceous species under the reaction conditions. On the other hand, the adsorbed phenol on Ni site underwent steam reforming, and the reaction was promoted by Fe.