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 NH 3 and toluene on sulfur tolerant nonconventional tungsten-based catalysts [tungsten carbide (WC) and tungstated zirconia (WZ)] at temperatures <750 °C in the presence of H 2 , CO, CO 2 , and H 2 O, 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 NH 3 and toluene decomposition were investigated. The NH 3 and toluene decomposition reactions were conducted at typical hot gas cleanup conditions of 700 °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 NH 3 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, CO 2 , and H 2 O had a somewhat negative impact on the high activities of WC and WZ for NH 3 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 NH 3 and toluene in the presence of H 2 , CO, CO 2 , and H 2 O. 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.