Browsing by Author "Simell, Pekka, Dr., Technical Research Centre of Finland VTT, Finland"

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  • Catalytic clean-up of biomass derived gasification gas with zirconia based catalysts
    (2014) Rönkkönen, Ella Hanne
     School of Chemical Technology | Doctoral dissertation (article-based)
    Biomass gasification is an efficient and environmentally friendly alternative to produce bioenergy and contribute to resolving future energy needs. The impurities of the gasification gas, such as tar and ammonia, need to be removed to enable the use of the gas in any of its applications such as in electricity or liquid biofuels production. Catalytic hot gas clean-up is an efficient method to decompose both hydrocarbons and ammonia. Several zirconia, precious metal and nickel catalysts were examined for the decomposition of tar and ammonia from synthetic gasification gas mixtures resembling gas from air blown gasification or from oxygen blown gasification. La2O3-ZrO2 was sulfur tolerant and decomposed tar and ammonia in selective oxidation reactions even at 600-700 °C and was more selective to higher molecular weight tar naphthalene than towards lighter tar compound toluene. La2O3-ZrO2 proved to be the most active of the zirconia based catalysts with sulfur containing gas. Characterization revealed that doping of zirconia with lanthanum favorably affected the redox and basic properties and thereby enhanced the activity towards tar in complex sulfur containing gas mixtures compared to ZrO2, SiO2-ZrO2 and Y2O3-ZrO2. Rh/La2O3-ZrO2 proved to be the most active of the studied mono- and bimetallic catalysts. It decomposed tar model compounds completely in reforming reactions at 900 °C and was more sulfur resistant and stable than the studied nickel catalysts. The ammonia conversion on Rh/La2O3-ZrO2 in the presence of sulfur was, however, very low. The sulfur poisoning of Rh/La2O3-ZrO2 was shown to be reversible. La2O3-ZrO2 and Rh/La2O3-ZrO2 together could be efficient and more sulfur resistant alternatives for nickel catalysts in gas clean-up, e.g. in a two staged reforming unit.