Mechanistic differences in the selective reduction of NO by propene over cobalt- and silver-promoted alumina catalysts: kinetic and in situ DRIFTS study |
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Authors: | F C Meunier V Zuzaniuk J P Breen M Olsson and J R H Ross |
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Affiliation: | Centre for Environmental Research, University of Limerick, Limerick, Ireland |
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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. |
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Keywords: | NO NO2 Propene Silver Cobalt Alumina Sulphate DRIFTS |
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