Simultaneous Ammonia and Toluene Decomposition on Tungsten-Based Catalysts for Hot Gas Cleanup

The current paper reports the results of a study of the simultaneous decomposition of NH3 and toluene on sulfur tolerant nonconventional tungsten-based catalysts (tungsten carbide (WC) and tungstated zirconia (WZ)] at temperatures <750 degrees C in the presence of H-2, CO, CO2, and H2O, such as it would be present in hot gas cleanup following biomass gasification. Toluene was chosen as a model compound to represent tars. The effects of addition of each gasification gas component on the activities of WC and WZ for NH3 and toluene decomposition were investigated. The NH3 and toluene decomposition reactions were conducted at typical hot gas cleanup conditions of 700 degrees C and 1 atm. In the absence of gasification gases. low activities were observed for toluene decomposition on WC and WZ while complete conversion of 4000 ppm of NH3 was observed at space velocities of 5 800 000 and 385 000 h(-1) for WC and WZ, respectively. The presence of H-2 CO, CO2, and H2O had a somewhat negative impact on the high activities of WC and WZ for NH3 decomposition while it had a positive impact on the toluene decomposition activities of both the catalysts. However, both WC and WZ were active for the simultaneous removal of NH3 and toluene in the presence of H-2 CO, CO2, and H2O. In the presence of gasification gases, both WC and WZ showed comparable performances for toluene decomposition on a per-g-catalyst basis with that of a commercial ultrastable Y zeolite (USY). However, on a per-m(2)-catalyst basis, WC showed by far the highest activity.