Olivine as tar removal catalyst for biomass gasifiers: Catalyst characterization

In the present paper olivine is considered as a prospective in-bed tar removal catalyst for fluidized bed biomass gasifiers. The catalytic activity of olivine is investigated via steam reforming reaction of naphthalene as a model biomass tar compound. It is observed that the calcination of olivine improves the performance of the catalyst. Calcination of olivine is done with air at 900 °C for different treatment times. With increasing calcination time, tar conversion increases; more than 80% naphthalene conversion is observed with 10 h of calcination time for olivine, which is found to be an optimum as further increase in time up to 20 h does not improve the naphthalene conversion. The primary focus of this paper is to characterize the olivine catalysts under investigation (specific composition (Mg1.78, Fe0.13) SiO4) with different calcination times. Techniques such as BET-surface area analysis, XPS, Mössbauer spectroscopy, TPR, SEM/EDX analysis are used to understand the basic phenomena of calcination of olivine. Olivine is observed to be non porous. SEM/EDX show iron rich areas at the surface of olivine after calcination. Severe segregation of iron is observed at the surface due to calcination, which is found to be non-uniform. Mössbauer spectroscopy reveals the appearance of iron(III) phase in the olivine after calcination. Besides the catalytic activity towards tar reduction, olivine is also observed to be highly attrition resistant to be used as an in-bed additive for fluid bed and moving bed biomass gasifiers.