A kinetic and DRIFTS study of supported Pt catalysts for NO oxidation

Abstract

NO oxidation was studied over Pt/CeO 2 and Pt/SiO 2 catalysts. Apparent activation energies (E a ) of 31.4 and 40.6 kJ/mole were determined for Pt/CeO 2 and Pt/SiO 2 , respectively, while reaction orders for NO and O 2 were fractional and positive for both catalysts. Pre-treatment of the catalysts with SO 2 caused a decrease in the E a values, while the reaction orders were only slightly changed. In situ DRIFTS measurements indicated that high concentrations of nitrate species were formed on the surface of Pt/CeO 2 during NO oxidation, while almost no surface species could be detected on Pt/SiO 2 . The addition of SO 2 resulted in the formation of a highly stable sulfate at the expense of nitrate species and caused an irreversible loss of catalytic activity for Pt/CeO 2 .

Pt/Ce Pr1−O2 (x= 1 or 0.9) NO storage–reduction (NSR) catalysts

“…The inferior NSE obtained at 200 °C compared to 300 °C is consistent with our previous observations for ceria-based LNT catalysts and reflects either less complete regeneration of NOx storage sites at 200 °C (compared to 300 °C) and/or a more severe kinetic limitation with respect to NO oxidation to NO2 at 200 °C. Inferior NOx storage at 400 °C can be attributed to the relative thermal instability of surface cerium nitrates at this temperature, as documented in the literature [38,39].…”

“…Figure7 depicts the evolution of DRIFT spectra acquired for Pt/CeO2-N and Pt/Ce0.9Pr0.1O2-N during NOx storage at 200 ºC. For both samples, bands appear at ~1293 and 1169 cm -1 at short storage times, which may be assigned to the νas and νs vibrations of chelating nitrites, respectively [8,38,42]. A third band at 1558 cm -1 can be attributed to chelating bidentate nitrates [8].…”

Selective catalytic reduction of NO with NH3 over manganese substituted iron titanate catalyst: Reaction mechanism and H2O/SO2 inhibition mechanism study

“…and monodentate nitrate (1552 cm −1 ) showed some decrease in intensity, while bidentate nitrate (1581 cm −1 ) showed no obvious change during the whole process. Due to the adsorption and disturbance of H 2 O on the surface of catalyst (shoulder band at 1628 cm −1 for ı HOH vibration mode), the 3 low vibration mode of bridging nitrate showed some blue shift to 1248 cm −1 due to the reduction of splitting of 3 frequency [37]; the 3 low vibration mode of monodentate nitrate also appeared at 1284 cm −1 [36]. After the removal of H 2 O feed, the surface nitrate species recovered to the original level, similar as adsorbed NH 3 species.…”

Catalytic oxidation of NO over TiO2 supported platinum clusters I. Preparation, characterization and catalytic properties

“…The formed SO 3 may not only occupy the active sites for NO oxidation but also cover the support materials by forming sulfates. As a result, serious deactivation by SO 2 is generally observed on catalysts for NO oxidation [36][37][38]. In this work, SO 2 -resistant TiO 2 is selected as the support for platinum and the formation sulfates on support is greatly prohibited.…”