Brønsted-NH4+ mechanism versusnitrite mechanism: new insight into the selective catalyticreduction of NO by NH3
- 29 October 2010
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Physical Chemistry Chemical Physics
- Vol. 13 (2), 453-460
- https://doi.org/10.1039/c0cp00256a
Abstract
The selective catalytic reduction (SCR) of NO by NH3 over V2O5 -based catalysts is used worldwide to control NOx emission. Understanding the mechanisms involved is vital for the rational design of more effective catalysts. Here, we have performed a systematic density functional theory (DFT) study of a SCR reaction by using cluster models. Three possible mechanisms have been considered, namely (i) a Lewis acid mechanism, (ii) a Brønsted acid mechanism and (iii) a nitrite mechanism. Our calculations down-play the significance of mechanism (i) due to its high barrier as well as the incorrect reaction order. On the other hand, our calculations demonstrate that both mechanisms (ii) and (iii) can lead to a first order reaction with respect to NO with the predicted barriers being consistent with the experimental observations. Thus, we conclude: there exists two competitive pathways for SCR. Mechanism (ii) is dominant when the Brønsted acidity of the catalysts is relatively strong, while mechanism (iii) becomes important when Brønsted acidity is weak or absent. Importantly, we demonstrate that the latter two mechanisms share a common feature where N–N bond formation is ahead of N–H bond cleavage, in contrast to that in mechanism (i). Such a sequence provides an effective way to reduce the side reaction of ammonia combustion since the relatively strong N–N bond has already been formed.Keywords
This publication has 61 references indexed in Scilit:
- Mechanisms of Methane Activation and Transformation on Molybdenum Oxide Based CatalystsJournal of the American Chemical Society, 2005
- Modeling catalytic reduction of NO by ammonia over V2O5Surface Science Reports, 2004
- NH3 Adsorption on the Brönsted and Lewis Acid Sites of V2O5(010): A Periodic Density Functional StudyThe Journal of Physical Chemistry B, 1999
- Reactivity of Lattice Oxygens Present in V2O5(010): A Periodic First-Principles InvestigationThe Journal of Physical Chemistry B, 1999
- Chemical and mechanistic aspects of the selective catalytic reduction of NO by ammonia over oxide catalysts: A reviewApplied Catalysis B: Environment and Energy, 1998
- Mechanism of the Vanadium Oxide-Catalyzed Selective Reduction of NO by NH3. A Quantum Chemical ModelingThe Journal of Physical Chemistry A, 1997
- Selective Catalytic Reduction of Nitric Oxide by Ammonia over V2O5/TiO2, V2O5/TiO2/SiO2, and V2O5−WO3/TiO2 Catalysts: Effect of Vanadia Content on the Activation EnergyIndustrial & Engineering Chemistry Research, 1996
- Temperature-programmed desorption/reaction and in situ spectroscopic studies of vanadia/titania for catalytic reduction of nitric oxideJournal of Catalysis, 1992
- Ab initio effective core potentials for molecular calculations. Potentials for K to Au including the outermost core orbitalsThe Journal of Chemical Physics, 1985
- Activities of vanadium pentoxide/titanium dioxide and vanadium pentoxide/aluminum oxide catalysts for the reaction of nitric oxide and ammonia in the presence of oxygenIndustrial & Engineering Chemistry Product Research and Development, 1982