The involvement of the reaction of surface nitrate [NO3 -(ads)] species with different reductants (C3H6, C2H5OH and CH3OH) in the selective catalytic reduction of nitrogen oxides (NO(x)) over a Ag/Al2O3 catalyst has been studied by in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and temperature-programmed desorption (TPD). When an NO/O2 mixture was exposed to a Ag/Al2O3 catalyst at 150°C, three kinds of nitrate species (bridging, monodentate and bidentate) were observed by DRIFT. The thermal stability of the monodentate NO3 -(ads) species was higher than that of the bridging and bidentate NO3 -(ads) species, which was confirmed by DRIFT and TPD measurements. The monodentate NO3 -(ads) species reacted effectively with C2H5OH and CH3 OH in the presence of O2 to form surface isocyanate [NCO(ads)] species at 250°C, whereas the bridging and bidentate NO3 -(ads) species reacted minimally. All NO3 -(ads) species were largely unreactive with C3H6 in the presence of O2 at temperatures below 250°C. On the other hand, the order of reactivity in the reduction of NO(x) at temperatures below 350°C was in good agreement with that of both the reactivity of the monodentate NO3 -(ads) species and the ease of NCO(a) formation (C2H5OH > CH3OH > C3H6). Based on these findings, the involvement of the reactivity of NO3 -(ads) species and the formation of NCO(ads) species in the selective reduction of NO(x) are discussed.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry