Development of zirconia catalysts for hot gas cleanup

Cleaning of gasification gas is essential, because tar may cause operational problems in downstream processes. Zirconia catalysts are active in tar decomposition with minor tendency to coking and deactivation by sulfur. This study describes the catalyst testing carried out in different scales. Ceramic monoliths were coated with slurries prepared from powders. At first the samples were made only for a small scale testing, after which a catalyst for slip-stream tests was selected. In the laboratory tests all the studied modified zirconias (undoped and three different dopants coded A, B, A-C) showed the activity of ca. 50 % in the tar decomposition already at 600°C. The maximum tar conversion with different dopants is reached at the temperature of 800 °C or higher. The most stable conversion at the measured temperature range was measured with the A-C zirconia, having tar conversion around 90%. The doping of zirconia has clearly a positive effect on the catalytic activity in tar decomposition. With the best dopant, a high conversion at the wide temperature range was measured giving flexibility in the process development of the catalytic reforming unit for the cleaning of the gasification gas.