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/gamma -Al2O3 catalysts for the C3H6-SCR of NO was about 8.7 x 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 N-2 (flavoured on low loading materials). The effect of the residence time was also investigated on a 1.2 wt.% Ag/gamma -Al2O3. The use of low space velocities enabled to obtain high conversion to N-2 at low temperatures and significantly reduced the amount of propene wasted by unselective combustion. The resistance of Ag, Ni, Co and In/gamma -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. (C) 2001 Elsevier Science B.V. All rights reserved.