Characterization and FTIR studies of MnO x-CeO 2 catalyst for low-temperature selective catalytic reduction of NO with NH 3

Gongshin Qi; Ralph T. Yang

doi:10.1021/jp048431h

Characterization and FTIR studies of MnO _x-CeO ₂ catalyst for low-temperature selective catalytic reduction of NO with NH ₃

Gongshin Qi
, Ralph T. Yang

Department of Chemical and Biological Engineering

University at Buffalo

University of Michigan, Ann Arbor

Research output: Contribution to journal › Article › peer-review

504 Scopus citations

Abstract

A series of high-activity manganese-cerium oxide catalysts for the low-temperature (373-453 K) selective catalytic reduction (SCR) of NO _x with ammonia were prepared. They were prepared by using the citric acid method (CA), coprecipitation method (CP), and impregnation method (IM) and were characterized by XRD, ESR, XPS, and FTIR techniques. A sample prepared by the CA method, MnO _x(0.3)-CeO ₂(923), showed the highest activity. XRD results showed that the catalyst prepared by the CA method had the smallest particle size and the weakest XRD peak intensity. Using ESR and XPS, Mn ⁴⁺, Mn ³⁺, and Mn ²⁺ oxide species were found'after calcination in air. Three kinds of Mn phases existed in the MnO _x-CeO ₂ catalysts that were prepared by the CA method: (1) aggregated Mn ₂O ₃ on the CeO ₂ support, (2) highly dispersed Mn ₂O ₃ with strong interactions with CeO ₂, and (3) Mn atoms incorporated into the CeO ₂ lattice. The distribution of Mn species depends on the preparation methods. Any oxygen vacancy formed in the CeO ₂ lattice caused by incorporation of Mn atoms adsorbs and activates molecular oxygen to form active oxygen species. Thus, the high activity of MnO _x(0.3)-CeO ₂(923) is attributed to the highly dispersed Mn species and the more active oxygen species that is formed. Ammonia molecules adsorbed onto MnO _x(0.3)-CeO ₂(923) to form NH ₄ ⁺ and coordinated NH ₃. At the same time, NH ₂ was observed because of H-abstraction. NO ₂, nitrite, and nitrate were formed by oxidation of NO. A mechanistic pathway for this reaction was proposed on the basis of earlier findings and the FTIR results obtained in this work. The initial step was adsorption of NH ₃ onto the Lewis acid sites, and then, the NH ₂ species was formed, followed by reaction between NH ₂ and NO to produce N ₂ and H ₂O. Possible intermediates are proposed, and all the intermediates could transform into NH ₂NO, which could further react to produce N ₂ and H ₂O.

Original language	English
Pages (from-to)	15738-15747
Number of pages	10
Journal	Journal of Physical Chemistry B
Volume	108
Issue number	40
DOIs	https://doi.org/10.1021/jp048431h
State	Published - Oct 7 2004

Access to Document

10.1021/jp048431h

Cite this

@article{24d353284fe24a91a3ca4a2bfa8688a8,

title = "Characterization and FTIR studies of MnO x-CeO 2 catalyst for low-temperature selective catalytic reduction of NO with NH 3",

abstract = "A series of high-activity manganese-cerium oxide catalysts for the low-temperature (373-453 K) selective catalytic reduction (SCR) of NO x with ammonia were prepared. They were prepared by using the citric acid method (CA), coprecipitation method (CP), and impregnation method (IM) and were characterized by XRD, ESR, XPS, and FTIR techniques. A sample prepared by the CA method, MnO x(0.3)-CeO 2(923), showed the highest activity. XRD results showed that the catalyst prepared by the CA method had the smallest particle size and the weakest XRD peak intensity. Using ESR and XPS, Mn 4+, Mn 3+, and Mn 2+ oxide species were found'after calcination in air. Three kinds of Mn phases existed in the MnO x-CeO 2 catalysts that were prepared by the CA method: (1) aggregated Mn 2O 3 on the CeO 2 support, (2) highly dispersed Mn 2O 3 with strong interactions with CeO 2, and (3) Mn atoms incorporated into the CeO 2 lattice. The distribution of Mn species depends on the preparation methods. Any oxygen vacancy formed in the CeO 2 lattice caused by incorporation of Mn atoms adsorbs and activates molecular oxygen to form active oxygen species. Thus, the high activity of MnO x(0.3)-CeO 2(923) is attributed to the highly dispersed Mn species and the more active oxygen species that is formed. Ammonia molecules adsorbed onto MnO x(0.3)-CeO 2(923) to form NH 4 + and coordinated NH 3. At the same time, NH 2 was observed because of H-abstraction. NO 2, nitrite, and nitrate were formed by oxidation of NO. A mechanistic pathway for this reaction was proposed on the basis of earlier findings and the FTIR results obtained in this work. The initial step was adsorption of NH 3 onto the Lewis acid sites, and then, the NH 2 species was formed, followed by reaction between NH 2 and NO to produce N 2 and H 2O. Possible intermediates are proposed, and all the intermediates could transform into NH 2NO, which could further react to produce N 2 and H 2O.",

author = "Gongshin Qi and Yang, \{Ralph T.\}",

year = "2004",

month = oct,

day = "7",

doi = "10.1021/jp048431h",

language = "English",

volume = "108",

pages = "15738--15747",

journal = "Journal of Physical Chemistry B",

issn = "1520-6106",

publisher = "American Chemical Society",

number = "40",

}

TY - JOUR

T1 - Characterization and FTIR studies of MnO x-CeO 2 catalyst for low-temperature selective catalytic reduction of NO with NH 3

AU - Qi, Gongshin

AU - Yang, Ralph T.

PY - 2004/10/7

Y1 - 2004/10/7

N2 - A series of high-activity manganese-cerium oxide catalysts for the low-temperature (373-453 K) selective catalytic reduction (SCR) of NO x with ammonia were prepared. They were prepared by using the citric acid method (CA), coprecipitation method (CP), and impregnation method (IM) and were characterized by XRD, ESR, XPS, and FTIR techniques. A sample prepared by the CA method, MnO x(0.3)-CeO 2(923), showed the highest activity. XRD results showed that the catalyst prepared by the CA method had the smallest particle size and the weakest XRD peak intensity. Using ESR and XPS, Mn 4+, Mn 3+, and Mn 2+ oxide species were found'after calcination in air. Three kinds of Mn phases existed in the MnO x-CeO 2 catalysts that were prepared by the CA method: (1) aggregated Mn 2O 3 on the CeO 2 support, (2) highly dispersed Mn 2O 3 with strong interactions with CeO 2, and (3) Mn atoms incorporated into the CeO 2 lattice. The distribution of Mn species depends on the preparation methods. Any oxygen vacancy formed in the CeO 2 lattice caused by incorporation of Mn atoms adsorbs and activates molecular oxygen to form active oxygen species. Thus, the high activity of MnO x(0.3)-CeO 2(923) is attributed to the highly dispersed Mn species and the more active oxygen species that is formed. Ammonia molecules adsorbed onto MnO x(0.3)-CeO 2(923) to form NH 4 + and coordinated NH 3. At the same time, NH 2 was observed because of H-abstraction. NO 2, nitrite, and nitrate were formed by oxidation of NO. A mechanistic pathway for this reaction was proposed on the basis of earlier findings and the FTIR results obtained in this work. The initial step was adsorption of NH 3 onto the Lewis acid sites, and then, the NH 2 species was formed, followed by reaction between NH 2 and NO to produce N 2 and H 2O. Possible intermediates are proposed, and all the intermediates could transform into NH 2NO, which could further react to produce N 2 and H 2O.

AB - A series of high-activity manganese-cerium oxide catalysts for the low-temperature (373-453 K) selective catalytic reduction (SCR) of NO x with ammonia were prepared. They were prepared by using the citric acid method (CA), coprecipitation method (CP), and impregnation method (IM) and were characterized by XRD, ESR, XPS, and FTIR techniques. A sample prepared by the CA method, MnO x(0.3)-CeO 2(923), showed the highest activity. XRD results showed that the catalyst prepared by the CA method had the smallest particle size and the weakest XRD peak intensity. Using ESR and XPS, Mn 4+, Mn 3+, and Mn 2+ oxide species were found'after calcination in air. Three kinds of Mn phases existed in the MnO x-CeO 2 catalysts that were prepared by the CA method: (1) aggregated Mn 2O 3 on the CeO 2 support, (2) highly dispersed Mn 2O 3 with strong interactions with CeO 2, and (3) Mn atoms incorporated into the CeO 2 lattice. The distribution of Mn species depends on the preparation methods. Any oxygen vacancy formed in the CeO 2 lattice caused by incorporation of Mn atoms adsorbs and activates molecular oxygen to form active oxygen species. Thus, the high activity of MnO x(0.3)-CeO 2(923) is attributed to the highly dispersed Mn species and the more active oxygen species that is formed. Ammonia molecules adsorbed onto MnO x(0.3)-CeO 2(923) to form NH 4 + and coordinated NH 3. At the same time, NH 2 was observed because of H-abstraction. NO 2, nitrite, and nitrate were formed by oxidation of NO. A mechanistic pathway for this reaction was proposed on the basis of earlier findings and the FTIR results obtained in this work. The initial step was adsorption of NH 3 onto the Lewis acid sites, and then, the NH 2 species was formed, followed by reaction between NH 2 and NO to produce N 2 and H 2O. Possible intermediates are proposed, and all the intermediates could transform into NH 2NO, which could further react to produce N 2 and H 2O.

UR - https://www.scopus.com/pages/publications/6044228090

U2 - 10.1021/jp048431h

DO - 10.1021/jp048431h

M3 - Article

SN - 1520-6106

VL - 108

SP - 15738

EP - 15747

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

IS - 40

ER -

Characterization and FTIR studies of MnO _x-CeO ₂ catalyst for low-temperature selective catalytic reduction of NO with NH ₃

Abstract

Access to Document

Other files and links

Fingerprint

Cite this