Molecular origins of selectivity in the reduction of NO x by NH 3

Donghai Sun, William F. Schneider, James Adams, Debasis Sengupta

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

The fundamental principle underlying the selective catalytic reduction (SCR) of NO x to N 2 is the promotion of reactions of reductant with NO x over competing, and thermodynamically preferred, reactions with a large excess of O 2. A similar competition between NO x and O 2 exists in the noncatalytic, thermal reduction of NO x with NH 3. In this work, density functional theory calculations are used to elucidate the origins of the remarkable selectivity in thermal deNO x. Thermal deNO x is initiated by the conversion of NH 3 into the active reductant, NH 2 radical. NH 2 radical reacts with NO at rates typical of gas-phase radical reactions to produce a relatively strongly bound H 2NNO adduct that readily rearranges and decomposes to N 2 and H 2O. In contrast, NH 2 radical reacts exceedingly slowly with O 2: the H 2N-OO adduct is weakly bound and more readily falls apart than reacts to products. The pronounced discrimination of NH 2 against reaction with O 2 is unusual behavior for a radical but can be understood through comparison of the electronic structures of the H 2NNO and H 2NOO radical adducts. These two key elements of thermal deNO x-reductant activation and kinetic inhibition of reactions with O 2-are similarly essential to successful catalytic lean NO x reduction, and are important to consider in evaluating and modeling NO x SCR.

Original languageEnglish (US)
Pages (from-to)9365-9374
Number of pages10
JournalJournal of Physical Chemistry A
Volume108
Issue number43
DOIs
StatePublished - Oct 28 2004

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Reducing Agents
selectivity
Selective catalytic reduction
adducts
Electronic structure
Density functional theory
Gases
Chemical activation
promotion
Kinetics
discrimination
Hot Temperature
activation
vapor phases
density functional theory
electronic structure
kinetics
products

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Molecular origins of selectivity in the reduction of NO x by NH 3 . / Sun, Donghai; Schneider, William F.; Adams, James; Sengupta, Debasis.

In: Journal of Physical Chemistry A, Vol. 108, No. 43, 28.10.2004, p. 9365-9374.

Research output: Contribution to journalArticle

Sun, Donghai ; Schneider, William F. ; Adams, James ; Sengupta, Debasis. / Molecular origins of selectivity in the reduction of NO x by NH 3 In: Journal of Physical Chemistry A. 2004 ; Vol. 108, No. 43. pp. 9365-9374.
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