Hydrogen assisted urea-SCR and NH3-SCR with silver–alumina as highly active and SO2-tolerant de-NOx catalysis

Addition of 0.5% H2 in the selective catalytic reduction of NO by urea (urea-SCR) caused a drastic improvement of NO reduction activity of Ag/Al2O3. Among various silver-based catalysts Ag/Al2O3 showed highest activity for H2 assisted urea-SCR, and high NO conversion (above 84%) and no formation of N2O were achieved over wide temperature range (200–500 °C) at GHSV of 75,000 h−1. After H2 assisted urea-SCR at 250 °C with 10% H2O and 50 ppm SO2 under GHSV of 380,000 h−1 for 24 h, NO conversion over Ag/Al2O3 decreased from 48 to 30%, though original activity was recovered when the deactivated catalyst was heated at 500 °C in the urea-SCR condition for 1 h. The catalyst also showed high SO2-tolerance in H2 assisted NH3-SCR at 200 °C.