Carbon deposition on a Ni/Al2O3 catalyst in low-temperature gasification using C6-hydrocarbons as surrogate biomass tar

C6-hydrocarbons, namely, n-hexane, 1-hexene, cyclohexane, and benzene, were selected as surrogate tar in low-temperature gasification (LTG) of biomass in the study of carbon deposition of organic compounds on a Ni/Al2O3 catalyst. All the compounds showed a two-stage weight increase due to carbon deposition; the two stages were the low-temperature stage (LTS: 300–650 °C) and high-temperature stage (HTS: above 650 °C). The LTS is the focus of this study. The susceptibility of the catalyst to carbon deposition was measured by the temperature (Tmax) giving maximum rate of weight increase (rmax). 1-hexene was found to be the most influential compound with the lowest Tmax and the highest rmax, followed by benzene. The saturated hydrocarbons, n-hexane and cyclohexane, were the least influential compounds for carbon deposition. The morphology of the deposits was found to be mainly herringbone-type carbon nanofibers, determined by transmission electron microscopy. Thermodynamic calculation revealed that 1-hexene was the most reactive compound for carbon deposition, while benzene was the most stable compound. The factors determining the carbon deposition of hydrocarbon compounds were explained in terms of both thermodynamic and adsorptive properties of the compounds.