Performance of Cu-Natural Chabazite During Selective Catalytic Reduction of NO with NH3-Effect of H2O Vapor and Metal Content.

We studied the effect of 5% v/v of water vapor during the Selective Catalytic Reduction of NO with NH3 (NH3-SCR-NO) using natural chabazite exchanged with Cu (1.3, 2.8 and 6.5-Cu/CHA) as the catalyst. The conversion of NO decreases slightly during light-off in the presence of water, but it reaches higher values in the range of temperature required for normal engine operation (280–420 °C). The maximum conversion at 350 °C increased with the Cu content, from 50% for 1.3-Cu/CHA to 90 and 95% with 2.8-Cu/CHA and 6.5-Cu/CHA, respectively. The initial Cu2+/Cu ratio was determined by H2-TPR, and the activity correlates with the fraction of Cu2+ species, which appears to be responsible for the NO reduction activity. During a test of the 2.8-Cu/CHA catalyst for 24 h we observed and modelled a small decay in activity observed during the first 3 h on-stream. The conversion remained stable thereafter, with or without 5% water in the feedstream. [ABSTRACT FROM AUTHOR]