Green synthesis of Ni supported hematite catalysts for syngas production from catalytic cracking of toluene as a model compound of biomass tar

In this work, natural limonite (NL) was selected as the precursor of hematite (H) to prepare the Ni-based catalysts (Nix/H) for catalytic cracking of toluene. The influences of nickel loading and reaction temperature on catalytic cracking of toluene as well as the lifetime of catalyst were evaluated and the gas products were determined. The catalysts before and after catalytic cracking were characterized by XRD (X-ray diffraction), H2-TPR (H2 temperature-programmed reduction), TEM (Transmission electron microscopy), XPS (X-ray photoelectron spectroscopy). The results showed that the catalytic activity of Nix/H was obviously improved after the Ni addition due to the formation of Ni-Fe alloy. Toluene conversion increased at first with increasing of Ni loading from 0 to 6% and then decreased from 6 to 10%. High toluene conversion of 96% and stability were achieved as the Ni loading was 6% at the reaction temperature of 800 °C. Meanwhile, toluene was mainly decomposed into CO, H2, CH4, CO2 and hematite was transformed into magnetite due to the consumption of active lattice oxygen during the catalytic cracking reaction. However, the decrease in catalytic activity of Nix/H with the increase of reaction time should be attributed to the metal carbide type coke formation.