Characterization of the active species in the silver/alumina system for lean NOx reduction with methanol

Low-temperature activity and selectivity for lean NOx reduction over silver/alumina is strongly dependent on the composition of surface silver species. This motivates the present investigation of the role of the supported silver species for the lean NOx reduction with methanol. The catalyst samples, with different composition of silver species, are characterized by temperature programmed desorption of ammonia (NH3-TPD), temperature programmed reduction with hydrogen (H-2-TPR) and temperature programmed desorption with NO (NO-TPD) in oxygen excess. The small differences in acidity do not significantly influence the lean NOx reduction with methanol. However, comparison of results from H-2-TPR experiments with previous characterization by UV-vis spectroscopy shows that fairly small silver species are reduced by hydrogen, possibly small silver clusters. These small silver species are likely, in addition to others, involved in the lean NOx reduction reactions. NO-TPD experiments, in the presence of oxygen and hydrogen, reveal a shift in temperature for one of the desorption peaks from the different samples. This peak is likely related to the shift in temperature for NOx reduction during methanol-SCR conditions for the compared samples. (C) 2016 Elsevier B.V. All rights reserved.