Fluidizable NiO–Fe₂O₃/SiO₂–ΓAl₂O₃ for tar (toluene) conversion in biomass gasification

This communication reports synergetic effects of bimetallic Ni–Fe on NiO–Fe₂O₃/SiO₂–γAl₂O₃ catalysts for biomass tar (toluene) conversion. The catalysts were successfully synthesized using a one-pot, solvent-deficient method and characterized using XRD, N₂ adsorption isotherm and NH₃-TPD techniques. The introduction of SiO₂ enhanced thermal stability of the NiO–Fe₂O₃/SiO₂–γAl₂O₃ catalysts, as observed in XRD and BET surface area analysis. The synthesized NiO–Fe₂O₃/SiO₂–γAl₂O₃ catalysts showed high BET specific surface area (52–58 m²/g) even after calcination at 950 °C. The NH₃-TPD analysis exhibited that the addition of NiO significantly decreased the strong acid sites of the NiO–Fe₂O₃/SiO₂–γAl₂O₃ catalysts. The performance of the synthesized catalysts were evaluated in a fluidized CREC Riser Simulator using toluene as a tar model compound. The NiO containing NiO–Fe₂O₃/SiO₂–γAl₂O₃ catalyst yielded high toluene conversion with higher H₂ concentration in the produced gas, as compared to Fe₂O₃/SiO₂–γAl₂O₃ catalyst. The presence of nickel promoted both methane reforming and water-gas shift reactions, contributed to higher H₂ concentration in the producer gas. A gasification process model, as developed in Aspen Plus, also showed that hydrogen composition of the producer gas can also be enhanced by adjusting the gasification temperature, pressure and steam/biomass ratios. These results indicate that the NiO–Fe₂O₃/SiO₂–γAl₂O₃ catalyst has a great potential for industrial use since it is a relatively cheap, less toxic, and stable for extended period of gasification operation. The spent catalyst materials are also useful to produce other commercial products, such as Portland cement and glass-ceramics.