Precious metal catalysts in the clean-up of biomass gasification gas: Part 1: Monometallic catalysts and their impact on gasification gas composition

The performance of Rh, Ru, Pt, and Pd on modified commercial zirconia support (m-ZrO₂) was compared to a benchmark Ni/m-ZrO₂ catalyst in the presence of H₂S in the clean-up of gasification gas from tar, methane, and ammonia. The aim was to produce ultra clean gas applicable for liquid biofuel production. In general, the activity towards the decomposition decreased in the order of aromatic hydrocarbons, ethylene > methane > ammonia. Hydrocarbon decomposition on m-ZrO₂ supported Rh, Ni, and Ru catalysts mainly occurred at 800–900 °C through reforming and/or dealkylation reactions. Aromatic hydrocarbon decomposition reactions proceeded on Pt/m-ZrO₂ and Pd/m-ZrO₂ via oxidation reactions at temperatures of 600–800 °C, while at 900 °C, the reforming and/or dealkylation reactions were dominating also on Pt/m-ZrO₂ and Pd/m-ZrO₂ catalysts. During longer test runs of ten hours at 800 °C, the activity of the Rh/m-ZrO₂ catalyst declined in the presence of 100 ppm H₂S due to the sulfur poisoning effects, coke formation, and the particle size growth. Although the performance of Rh/m-ZrO₂ declined, it still remained better than Ni/m-ZrO₂ both towards naphthalene and total aromatic hydrocarbon, while only Ni/m-ZrO₂ and Ru/m-ZrO₂ decomposed ammonia in the presence of sulfur. Nevertheless, the most promising catalyst for clean gas production was Rh/m-ZrO₂.