SCR of NO with C₃H₆ in the presence of excess O ₂ over Cu/Ag/CeO₂-ZrO₂ catalyst

The catalytic activity of a series of CeO₂-ZrO₂ mixed oxides in the selective catalytic reduction (SCR) of NO by C₃H ₆ at 400 °C has been investigated. The NO reduction activity of pure CeO₂ is enhanced in the presence of Zr, reaching a maximum NO conversion with CeO₂(75)-ZrO₂(25) catalyst. Then, the catalytic performances of Cu(4)/Ag(1)/CeO₂ and Cu(4)/Ag(1)/CeO ₂(75)-ZrO₂(25) catalysts were compared and the latter showed better activity especially in the low temperature region (250-350 °C). The stronger metal-support interaction and higher reducibility shown by the Cu(4)/Ag(1)/CeO₂(75)-ZrO₂(25) catalyst were believed to enhance its performance compared to Cu(4)/Ag(1)/CeO₂ catalyst by activating more C₃H₆ to selectively reduce NO within this temperature region. Central composite response surface design methodology was employed to study the effect of operating variables such as temperature, NO and C₃H₆ concentrations on the SCR of NO by C ₃H₆ over Cu(4)/Ag(1)/CeO₂(75)-ZrO ₂(25) catalyst and to determine the optimum value of operating variables for maximum NO conversion. Numerical results indicated that the optimum NO conversion of 82.89% is attained at reaction temperature = 415.38 °C, NO concentration = 1827.16 ppm and C₃H₆ concentration = 1908.13 ppm. The addition of water vapor to the reactant significantly decreased the NO conversion over Cu(4)/Ag(1)/CeO₂ and Cu(4)/Ag(1)/CeO₂(75)-ZrO₂(25), but the inhibition was more pronounced over Cu(4)/Ag(1)/CeO₂ catalyst.