Mechanism of NO-SCR by methane over Co,H-ZSM-5 and Co,H-mordenite catalysts

F. Lónyi, Hanna E. Solt, Z. Pászti, J. Valyon

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

Results of X-ray photoelectron spectroscopic (XPS) examination and temperature-programmed reduction measurements by H2 (H2-TPR) showed that the Co-zeolite catalysts, which were found most active in the selective catalytic reduction of NO by methane to N2 in the presence of excess O2 (NO-SCR), contain both Co2+/[Co-OH]+/H+ exchange cations, Co-oxo species and cobalt oxide clusters. Using operando Diffuse Reflectance Infrared Fourier Transform Spectroscopic method (DRIFTS method) the NO-SCR reaction was shown to proceed in consecutive steps via bifunctional mechanism over active sites (i) promoting the oxidation of NO by O2 to NO2 (NO-COX reaction), and sites (ii) whereon disproportionation and charge separation of 2NO2 generates activated surface intermediate NO3-/NO+ ion pair. Latter process was found to require Co2+ zeolite cations. The NO-COX reaction was shown to proceed over Co-oxo species and cobalt oxide, if present, and also over Brønsted acid sites but at a significantly lower rate. In the reaction of methane and the NO3-/NO+ ion pair CO2, H2O, and N2 was formed and the active Co2+ sites were recovered (CH4/NO-SCR reaction). The surface concentration of the NO3-/NO+ ion pair must have been controlled by the relative magnitude of the apparent rate constants of the consecutive NO-COX and CH4/NO-SCR reactions. Below about 700K reaction temperature latter reaction governed the rate of the consecutive NO reduction process. Above about 700K combustion became the main reaction of methane. Because of the low equilibrium NO2 concentration at these high temperatures the NO-COX reaction took over the control over the rate of the NO-SCR process. Under steady state reaction conditions a temperature-dependent fraction of the Co2+ active sites was always poisoned by adsorbed H2O formed in the CH4 oxidation reaction.

Original languageEnglish
Pages (from-to)218-229
Number of pages12
JournalApplied Catalysis B: Environmental
Volume150-151
DOIs
Publication statusPublished - May 5 2014

Fingerprint

mordenite
Methane
Thyristors
methane
catalyst
Catalysts
Zeolites
cobalt
zeolite
ion
oxide
Cations
Cobalt
Ions
oxidation
Positive ions
temperature
Oxidation
Temperature
Selective catalytic reduction

Keywords

  • Co,H-zeolites
  • NO-SCR by CH
  • Operando-DRIFTS
  • Reaction mechanism

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology
  • Environmental Science(all)

Cite this

Mechanism of NO-SCR by methane over Co,H-ZSM-5 and Co,H-mordenite catalysts. / Lónyi, F.; Solt, Hanna E.; Pászti, Z.; Valyon, J.

In: Applied Catalysis B: Environmental, Vol. 150-151, 05.05.2014, p. 218-229.

Research output: Contribution to journalArticle

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abstract = "Results of X-ray photoelectron spectroscopic (XPS) examination and temperature-programmed reduction measurements by H2 (H2-TPR) showed that the Co-zeolite catalysts, which were found most active in the selective catalytic reduction of NO by methane to N2 in the presence of excess O2 (NO-SCR), contain both Co2+/[Co-OH]+/H+ exchange cations, Co-oxo species and cobalt oxide clusters. Using operando Diffuse Reflectance Infrared Fourier Transform Spectroscopic method (DRIFTS method) the NO-SCR reaction was shown to proceed in consecutive steps via bifunctional mechanism over active sites (i) promoting the oxidation of NO by O2 to NO2 (NO-COX reaction), and sites (ii) whereon disproportionation and charge separation of 2NO2 generates activated surface intermediate NO3-/NO+ ion pair. Latter process was found to require Co2+ zeolite cations. The NO-COX reaction was shown to proceed over Co-oxo species and cobalt oxide, if present, and also over Br{\o}nsted acid sites but at a significantly lower rate. In the reaction of methane and the NO3-/NO+ ion pair CO2, H2O, and N2 was formed and the active Co2+ sites were recovered (CH4/NO-SCR reaction). The surface concentration of the NO3-/NO+ ion pair must have been controlled by the relative magnitude of the apparent rate constants of the consecutive NO-COX and CH4/NO-SCR reactions. Below about 700K reaction temperature latter reaction governed the rate of the consecutive NO reduction process. Above about 700K combustion became the main reaction of methane. Because of the low equilibrium NO2 concentration at these high temperatures the NO-COX reaction took over the control over the rate of the NO-SCR process. Under steady state reaction conditions a temperature-dependent fraction of the Co2+ active sites was always poisoned by adsorbed H2O formed in the CH4 oxidation reaction.",
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AU - Solt, Hanna E.

AU - Pászti, Z.

AU - Valyon, J.

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N2 - Results of X-ray photoelectron spectroscopic (XPS) examination and temperature-programmed reduction measurements by H2 (H2-TPR) showed that the Co-zeolite catalysts, which were found most active in the selective catalytic reduction of NO by methane to N2 in the presence of excess O2 (NO-SCR), contain both Co2+/[Co-OH]+/H+ exchange cations, Co-oxo species and cobalt oxide clusters. Using operando Diffuse Reflectance Infrared Fourier Transform Spectroscopic method (DRIFTS method) the NO-SCR reaction was shown to proceed in consecutive steps via bifunctional mechanism over active sites (i) promoting the oxidation of NO by O2 to NO2 (NO-COX reaction), and sites (ii) whereon disproportionation and charge separation of 2NO2 generates activated surface intermediate NO3-/NO+ ion pair. Latter process was found to require Co2+ zeolite cations. The NO-COX reaction was shown to proceed over Co-oxo species and cobalt oxide, if present, and also over Brønsted acid sites but at a significantly lower rate. In the reaction of methane and the NO3-/NO+ ion pair CO2, H2O, and N2 was formed and the active Co2+ sites were recovered (CH4/NO-SCR reaction). The surface concentration of the NO3-/NO+ ion pair must have been controlled by the relative magnitude of the apparent rate constants of the consecutive NO-COX and CH4/NO-SCR reactions. Below about 700K reaction temperature latter reaction governed the rate of the consecutive NO reduction process. Above about 700K combustion became the main reaction of methane. Because of the low equilibrium NO2 concentration at these high temperatures the NO-COX reaction took over the control over the rate of the NO-SCR process. Under steady state reaction conditions a temperature-dependent fraction of the Co2+ active sites was always poisoned by adsorbed H2O formed in the CH4 oxidation reaction.

AB - Results of X-ray photoelectron spectroscopic (XPS) examination and temperature-programmed reduction measurements by H2 (H2-TPR) showed that the Co-zeolite catalysts, which were found most active in the selective catalytic reduction of NO by methane to N2 in the presence of excess O2 (NO-SCR), contain both Co2+/[Co-OH]+/H+ exchange cations, Co-oxo species and cobalt oxide clusters. Using operando Diffuse Reflectance Infrared Fourier Transform Spectroscopic method (DRIFTS method) the NO-SCR reaction was shown to proceed in consecutive steps via bifunctional mechanism over active sites (i) promoting the oxidation of NO by O2 to NO2 (NO-COX reaction), and sites (ii) whereon disproportionation and charge separation of 2NO2 generates activated surface intermediate NO3-/NO+ ion pair. Latter process was found to require Co2+ zeolite cations. The NO-COX reaction was shown to proceed over Co-oxo species and cobalt oxide, if present, and also over Brønsted acid sites but at a significantly lower rate. In the reaction of methane and the NO3-/NO+ ion pair CO2, H2O, and N2 was formed and the active Co2+ sites were recovered (CH4/NO-SCR reaction). The surface concentration of the NO3-/NO+ ion pair must have been controlled by the relative magnitude of the apparent rate constants of the consecutive NO-COX and CH4/NO-SCR reactions. Below about 700K reaction temperature latter reaction governed the rate of the consecutive NO reduction process. Above about 700K combustion became the main reaction of methane. Because of the low equilibrium NO2 concentration at these high temperatures the NO-COX reaction took over the control over the rate of the NO-SCR process. Under steady state reaction conditions a temperature-dependent fraction of the Co2+ active sites was always poisoned by adsorbed H2O formed in the CH4 oxidation reaction.

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