Global Kinetic Study of NO Reduction by NH₃ over V₂O₅–WO₃/TiO₂: Relationship between the SCR Performance and the Key Factors

Abstract

The nonselective catalytic reduction (NSCR) reaction and the catalytic oxidation of NH3 to NO (C–O reaction) simultaneously happened during the selective catalytic reduction (SCR) of NO with NH3 over V2O5–WO3/TiO2, especially at higher temperatures. There was an excellent linear relationship between the SCR reaction rate and gaseous NO concentration, and the intercept and slope can be used to describe the rate constant of NO reduction through the Langmuir–Hinshelwood mechanism and that through the Eley–Rideal mechanism, respectively. However, the NSCR reaction rate was nearly independent of gaseous NO concentration, and the reaction order of the C–O reaction with respect to gaseous NO concentration was much less than zero. According to the kinetic study, the relationship of the SCR performance (i.e., SCR activity and N2 selectivity) with the key factors (for example V2O5 content, H2O effect, and reactant concentration) was built, which can be used to predict the SCR performance.

The Role of Fe2O3 Species in Depressing the Formation of N2O in the Selective Reduction of NO by NH3 over V2O5/TiO2-Based Catalysts

“…As for NO and N 2 O in Figure 6a,b, all those N 2 peaks would be associated with ammonium ions and NH x on Bronsted and Lewis acid centers [43][44][45]. The NH x species are oxidized to N 2 via NO-assistant route, as discussed [11,39,48]. The presence of Fe 2 O 3 in VWT and c-VWT caused not only a shift of the major N 2 peak to lower temperatures, by 5-15 • C, but also a significant increase in their intensity, and such changes were greater for the commercial-based catalysts (Figure 6c(S3,S4)).…”

“…An intensity of the 650-680 • C N 2 O peak in VWT and 2.73% Fe 2 O 3 /VWT (S1 and S2) was very weak compared to that in the other samples (S3 and S4), which is in excellent agreement with the H 2 O production levels ( Figure 5b). All the unpromoted catalysts (spectra S1 and S3 in Figure 6b , is improbable and NH species on V 5+ =O sites reacts with gas-phase NO to form N 2 O and V 4+ -OH [11,39,48]. This represents that gaseous NO is essential for such N 2 O production, suggesting an involvement of NO molecules shown in Figure 6a because of no feed of NO upon NH 3 TPD experiments.…”

“…In addition to the main SCR reactions over V 2 O 5 -WO 3 (or MoO 3 )/TiO 2 catalysts, many side reactions can occur, and among them, one is the production of N 2 O that is a greenhouse gas with a global warming potential of 310 at a 100-year time horizon, and the extent of its emissions can greatly depend on the loading and crystallinity of V 2 O 5 , the secondary component, reaction temperature, concentrations of H 2 O and O 2 , and so forth [3,6,[11][12][13][14][15]. Such a formation of N 2 O in the NH 3 -SCR reaction is proposed by the following major routes [6,[12][13][14][15] …”

High Temperature and High Concentration SCR of NO with NH3 for the Oxyfuel Combustion Process: Fitting of Kinetics to Data from a Laboratory Reactor Experiment

“…Xiong [9] completed a thorough kinetic study of the SCR system and included the NSCR and the deep oxidation of NH 3 to NO. They showed that higher amounts of NO and NH 3 (in equimolar ratios) produced less N 2 O.…”

“…The renewed interest in N 2 O, which is normally present in the ppm range in the normal SCR reaction, is due to its high (298 times that of CO 2 ) global warming potential [8]. A recent experimental study examines the formation of N 2 O over V 2 O 5 -WO 3 /TiO 2 catalysts [9]. This thorough study covers a wide range of temperatures from 150 to 500 °C, NO contents up to 1000 ppm and V 2 O 5 contents from 1 to 5 wt%.…”