title: Reaction products and kinetics of the reaction of NO2 with γ-Fe2O3.
abstract: The reaction of NO(2) with Fe(2)O(3) has relevance for both atmospheric chemistry and catalysis. Most studies have focused on hematite, α-Fe(2)O(3), as it is the thermodynamic stable state of iron oxide; however, other forms of Fe(2)O(3) naturally occur and may have different chemistries. In this study, we have investigated the reaction products and kinetics for NO(2) reacting with γ-Fe(2)O(3) powder using diffuse reflectance infrared Fourier transform spectroscopy and compared the results to those of previous studies of NO(2) reacting with α-Fe(2)O(3). Both α- and γ-Fe(2)O(3) produce surface-bound nitrate at the pressures examined in this study (24-212 mTorr); surface-bound nitrite products are observed at all pressures for γ-Fe(2)O(3) whereas nitrite was only observed on α-Fe(2)O(3) at lower pressures. Surface-bound NO(+) and Fe-NO products are observed on γ-Fe(2)O(3), which have not been observed with α-Fe(2)O(3). The reaction kinetics show a first-order dependence on NO(2) pressure and this is used to support the hypothesis of unimolecular reaction of adsorbed NO(2) with the γ-Fe(2)O(3) surface as the slow step in the reaction mechanism. The difference in product formation between NO(2) reacting with γ-Fe(2)O(3) and previous studies of α-Fe(2)O(3) illustrate the fact that care must be taken in generalizing reactivity of different polymorphs.
authors.affiliation: Department of Chemistry, Susquehanna University, Selinsgrove, Pennsylvania 17870, United States.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Hixson
authors.forename: John W
authors.initials: JW
authors.lastname: Jordan
authors.forename: Erica L
authors.initials: EL
authors.lastname: Wagner
authors.forename: Holly M
authors.initials: HM
authors.lastname: Bevsek
mesh_terms: D000327:Adsorption; D005290:Ferric Compounds / Q000737:chemistry*; D007700:Kinetics; D009585:Nitrogen Dioxide / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide; D009585:Nitrogen Dioxide