NO Reduction by Urea under Lean Conditions over Single-Step Sol–Gel Cu/Alumina Catalyst

We present the catalytic activity of 1% Cu on alumina catalyst prepared using a single-step sol–gel process (designated 1% Cu–SG) as a function of oxygen, water, and SO2 in the feed for the reduction of NO with an aqueous urea solution. Our results show that NOx conversion activity of 1% Cu–SG is dependent on oxygen in the feed. The maximum conversion increased from 91 to 99% when the amount of oxygen in the feed was changed from 2 to 14%. Also, the location of maximum conversion temperature decreased from 400 to 377°C. Short-term and long-term exposure of the catalyst to a gas mixture containing 25 ppm SO2 did not result in activity loss at any temperature as long as aqueous urea was present in the feed. However, temporary interruption of aqueous urea solution resulted in permanent activity loss. Our attempt to reactivate the catalyst with propene failed to recover the original activity.