A highly carbon-resistant olivine thermally fused with metallic nickel catalyst for steam reforming of biomass tar model compound

Abstract

Olivine has been shown to have a good catalytic effect on biomass tar, however, carbon deposition is still one of the adverse conditions that affect its activity. A highly carbon-resistant olivine-supported metallic nickel catalyst, which was synthesized using thermal fusion (TF), was tested in a fixed bed reactor for tar removal. Toluene was selected as a tar destruction model molecule. The current work evaluated three catalysts, namely, raw olivine, TF-olivine (olivine calcined at 1400 °C in air) and TF-Ni/olivine (TF-olivine loaded with 5% wt Ni calcined at 1400 °C in Ar), for toluene steam reforming and investigated the effects of reaction temperature, steam to carbon molar ratio (S/C) and weight hourly space velocity (WHSV) on toluene conversion, carbon deposition and gas composition. Catalytic activity and resistance against carbon deposition were discussed based on physiochemical properties of the catalyst, including BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), temperature programmed reduction (TPR) and Laser Raman spectroscopy (LRS). The TF-Ni/olivine catalyst showed the best catalytic performance in terms of both toluene conversion and carbon deposition. A very low carbon deposition (less than 1%) was obtained when the S/C ratio was 0.88 and 1.02. Relative amounts of reducible Ni, Fe and Mg on the surface played a significant role in the catalytic behavior. Thermal fusion at a high temperature made the interaction between active metal and olivine structure stronger. The toluene conversion increased from 73.7% to 99.6% with the reaction temperature ranged from 750 °C to 950 °C, however it decreased form 92.4% to 82.6% when the WHSV increased from 0.77 h⁻¹ to 1.35 h⁻¹, similarly it decreased slightly (96.9% to 86.2%) with the S/C ratio ranging from 0.29 to 1.02. When comparing the characteristics between fresh and spent TF-Ni/olivine, the main structure and surface topography remained unchanged.