Abstract
The distribution of gaseous products and the nature of the surface species generated during the selective catalytic reduction of NO with C3H6 in the presence of excess O2 (i.e. C3H6-SCR) were studied over both a 0.4% Co/γ-Al2O3 catalyst and a sulphated 1.2% Ag/γ-Al2O3 catalyst. The results were compared with those previously reported for the C3H6-SCR over 1.2% Ag/γ-Al2O3 and γ-Al2O3. High concentrations of NO2 were observed in the product stream of the SCR reaction over the 0.4% Co/γ-Al2O3 and sulphated 1.2% Ag/γ-Al2O3 materials. The results show that (as in the case of the γ-Al2O3 and also probably that of the 1.2% Ag/γ-Al2O3) the NO2 was formed via an alternative route to the direct oxidation of NO with O2. The yields of NO2 were higher over the Co/γ-Al2O3 than over the other materials and in contrast to the other materials, no NH3 was produced over the Co/γ-Al2O3 catalyst. Based on these results and those of in situ DRIFTS experiments, a global reaction scheme incorporating organo-nitrogen species as key intermediates is proposed. In this scheme, NO, propene and oxygen react to form organo-nitro and/or organo-nitrito adsorbed species, the reaction products of which combine to yield N2. The results reported here suggest that Co preferentially promotes the formation of nitrito-compounds which can readily decompose to NO2, whereas Ag preferentially promotes the formation of nitro-compounds (from reaction of strongly bound ad-NOx species) which can decompose to isocyanates and ammonia. The sulphation of the 1.2% Ag/γ-Al2O3 reduced the surface concentration of strongly bound ad-NOx species which were thought to react with the reductant or derived species to yield the organo-nitrogen species.
Original language | English |
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Pages (from-to) | 287-304 |
Number of pages | 18 |
Journal | Catalysis Today |
Volume | 59 |
Issue number | 3 |
DOIs | |
Publication status | Published - 25 Jun 2000 |