Effect of the silver loading and some other experimental parameters on the selective reduction of NO with C₃H₆ over Al₂O₃ and ZrO₂-based catalysts

The present work reports data on the activity of silver, alumina and zirconia based-catalysts for the C₃H₆-SCR of NO. The optimum silver loading for Ag/γ-Al₂O₃ catalysts for the C₃H₆-SCR of NO was about 8.7 × 10^-5 g_silver m_alumina/^-2 which gave the best compromise between a higher activity at low temperatures (favoured on high loading materials) and a high selectivity to N₂ (favoured on low loading materials). The effect of the residence time was also investigated on a 1.2 wt.% Ag/γ-Al₂O₃. The use of low space velocities enabled to obtain high conversion to N₂ at low temperatures and significantly reduced the amount of propene wasted by unselective combustion. The resistance of Ag, Ni, Co and In/γ-Al₂O₃ catalysts to ex situ exposure to 100 ppm of SO₂ was studied. The silver sample was the most inhibited by SO₂ whereas the other samples were deactivated to a lower extent and showed partial regeneration with time on SO₂-free stream. The effect of a large concentration of water on the activity of these materials was investigated. All these catalysts showed a significant loss of activity in the presence of 12% water but this inhibition was fully reversible. Interestingly, the activity of the silver sample appeared to increase with time on wet stream. The activity of zirconia-based materials for the C₃H₆-SCR of NO was compared to that of alumina and zeolite-based catalysts. Silver-promoted ZrO₂ catalysts were active at lower temperatures but displayed greater selectivities to N₂O than that of the alumina-based samples.