Catalytic performance of monolithic Ir/SiO2 based catalysts for selective reduction of NO with CO

Ir/SiO2, Ir/WO3-SiO2 and Ba doped Ir/WO3-SiO2 powder catalysts have high activity for the selective reduction of NO with CO in the presence of O-2 (CO-SCR). The present study investigated the activity of these three Ir/SiO2-based catalysts in monolithic form for industrial applications. The catalytic activity was evaluated during heating and cooling cycles between 200 degrees C and 600 degrees C. All monolithic catalysts showed low activity for NO reduction during the first heating cycle but high activity appeared from the next cycle. The active temperatures for the monolithic catalysts are different to those for the powder catalysts, probably because of the differences in heat and mass transfer. The activities for CO-SCR gradually decreased with the number of cycles. The activity and durability of the monolith catalysts were consistent with those of the powder catalysts. Ba doped Ir/WO3-SiO2 monolith catalyst was the best catalyst. XRD spectroscopy showed that catalyst deactivation was caused by oxidation of iridium metal, which is the active species, because the activities of the aged catalysts were recovered by hydrogen reduction. The presence of SO2 in the reaction gas increased the activity of Ir/SiO2 catalyst, but had little effect on the activities of Ir/WO3-SiO2 and Ba doped Ir/WO3-SiO2 catalysts.