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 SCR of NO with CO in the presence of O₂ (CO-SCR). The activity of these three Ir/SiO₂-based catalysts was studied in monolithic form for industrial applications. The catalytic activity was evaluated during heating and cooling cycles between 200° and 600°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. 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.