Kinetics investigation of NO + CO reaction on La–Sr–Mn–O perovskite-type mixed oxides

• Published in: Applied catalysis. A, General Vol. 263; no. 2; pp. 227 - 239
• Main Authors: Leontiou, A.A, Ladavos, A.K, Armatas, G.S, Trikalitis, P.N, Pomonis, P.J
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 10.06.2004; Elsevier
• Subjects: Catalysis; Chemistry; Exact sciences and technology; General and physical chemistry; Kinetics; La–Sr–Mn–O; NO + CO reaction; Perovskites; Rietveld; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Perovskites; Kinetics; La–Sr–Mn–O; Rietveld; NO + CO reaction; Perovskite; La-Sr-Mn-O; Oxides
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2003.12.017

Substituted perovskite-type mixed oxides of the general formula La 1− x Sr x (Mn III/Mn IV)O 3± δ prepared by the nitrate method were examined by X-ray diffractometry (XRD) and the diffraction data were analyzed using the Rietveld refinement method. The amount of desorbed oxygen from the samples when heating in a He atmosphere was estimated with thermogravimetric O 2/temperature programmed desorption experiments while the amount of Mn III and Mn IV in the samples was determined iodometrically. The substitution of La 3+ by Sr 2+ leads to a gradual increase of Mn IV in the solids and to the transition from an oxygen excess state to an oxygen deficient one. The samples were checked as catalysts for the reaction NO+CO→products in a lab-scale plug–flow reactor between 220 and 560 °C. The reaction rate profiles were simulated using a relationship of the form R=w 1R low T +w 2R high T , where w 1, w 2 the weighing coefficients for the corresponding R at low R low T and high temperatures R high T . From the fitting data the true activation energies E 1 and E 2 were estimated for R low T and R high T as well as the heats of adsorption Δ H ads(NO) and Δ H ads(CO) for the NO and CO species. Finally, the values of E app/low T estimated from typical Arrhenius plots ln R= f(1/ T) at the low temperature region are in reasonable agreement with the difference E 1−Δ H ads(NO), a fact validating the results of simulation/fitting and indicating its usefulness for describing the reaction rates and estimating the kinetic and thermodynamic parameters controlling them. This methodology of simulation provides easily kinetic (activation energies) as well as thermodynamic (heats of adsorption) parameters which otherwise would necessitate differentiated experimental set-ups.