Assessing the effect of reducing agents on the selective catalytic reduction of NOx over Ag/Al2O3 catalysts

Carmine D'Agostino, S. Chansai, Isabelle Bush, Chensong Gao, M.D. Mantle, C. Hardacre, S.L. James, L.F. Gladden

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Abstract

The selective catalytic reduction (SCR) of NOx in the presence of different reducing agents over Ag/Al2O3 prepared by wet impregnation was investigated by probing catalyst activity and using NMR relaxation time analysis to probe the strength of surface interaction of the various reducing agent species and water. The results reveal that the strength of surface interaction of the reducing agent relative to water, the latter present in engine exhausts as a fuel combustion product and, in addition, produced during the SCR reaction, plays an important role in determining catalyst performance. Reducing agents with weak strength of interaction with the catalyst surface, such as hydrocarbons, show poorer catalytic performance than reducing agents with a higher strength of interaction, such as alcohols. This is attributed to the greater ability of oxygenated species to compete with water in terms of surface interaction with the catalyst surface, hence reducing the inhibiting effect of water molecules blocking catalyst sites. The results support the observations of earlier work in that the light off-temperature and maximum NOx conversion and temperature at which that occurs are sensitive to the reducing agent present during reaction, and the proposal that improved catalyst performance is caused by increased adsorption strength of the reducing agent, relative to water, at the catalyst surface. Importantly, the NMR relaxation time analysis approach to characterising the strength of adsorption more readily describes the trends in catalytic behaviour than does a straightforward consideration of the polarity (i.e., relative permittivity) of the reducing agents studied here. In summary, this paper describes a simple approach to characterising the interaction energy of water and reducing agent so as to aid the selection of reducing agent and catalyst to be used in SCR conversions.
Original languageEnglish
Pages (from-to)1661-1666
Number of pages6
JournalCATALYSIS SCIENCE & TECHNOLOGY
Volume6
Issue number6
Early online date30 Oct 2015
DOIs
Publication statusPublished - 21 Mar 2016

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Selective catalytic reduction
Reducing Agents
Reducing agents
Catalysts
Water
Relaxation time
Nuclear magnetic resonance
Vehicle Emissions
Adsorption
Exhaust systems (engine)
Hydrocarbons
Catalyst supports
Impregnation
Catalyst activity
Alcohols
Permittivity
Temperature
Molecules

Bibliographical note

Export Date: 5 April 2016

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D'Agostino, C., Chansai, S., Bush, I., Gao, C., Mantle, M. D., Hardacre, C., ... Gladden, L. F. (2016). Assessing the effect of reducing agents on the selective catalytic reduction of NOx over Ag/Al2O3 catalysts. CATALYSIS SCIENCE & TECHNOLOGY, 6(6), 1661-1666. https://doi.org/10.1039/c5cy01508a
D'Agostino, Carmine ; Chansai, S. ; Bush, Isabelle ; Gao, Chensong ; Mantle, M.D. ; Hardacre, C. ; James, S.L. ; Gladden, L.F. / Assessing the effect of reducing agents on the selective catalytic reduction of NOx over Ag/Al2O3 catalysts. In: CATALYSIS SCIENCE & TECHNOLOGY. 2016 ; Vol. 6, No. 6. pp. 1661-1666.
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D'Agostino, C, Chansai, S, Bush, I, Gao, C, Mantle, MD, Hardacre, C, James, SL & Gladden, LF 2016, 'Assessing the effect of reducing agents on the selective catalytic reduction of NOx over Ag/Al2O3 catalysts', CATALYSIS SCIENCE & TECHNOLOGY, vol. 6, no. 6, pp. 1661-1666. https://doi.org/10.1039/c5cy01508a

Assessing the effect of reducing agents on the selective catalytic reduction of NOx over Ag/Al2O3 catalysts. / D'Agostino, Carmine; Chansai, S.; Bush, Isabelle; Gao, Chensong; Mantle, M.D.; Hardacre, C.; James, S.L.; Gladden, L.F.

In: CATALYSIS SCIENCE & TECHNOLOGY, Vol. 6, No. 6, 21.03.2016, p. 1661-1666.

Research output: Contribution to journalArticle

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T1 - Assessing the effect of reducing agents on the selective catalytic reduction of NOx over Ag/Al2O3 catalysts

AU - D'Agostino, Carmine

AU - Chansai, S.

AU - Bush, Isabelle

AU - Gao, Chensong

AU - Mantle, M.D.

AU - Hardacre, C.

AU - James, S.L.

AU - Gladden, L.F.

N1 - Export Date: 5 April 2016

PY - 2016/3/21

Y1 - 2016/3/21

N2 - The selective catalytic reduction (SCR) of NOx in the presence of different reducing agents over Ag/Al2O3 prepared by wet impregnation was investigated by probing catalyst activity and using NMR relaxation time analysis to probe the strength of surface interaction of the various reducing agent species and water. The results reveal that the strength of surface interaction of the reducing agent relative to water, the latter present in engine exhausts as a fuel combustion product and, in addition, produced during the SCR reaction, plays an important role in determining catalyst performance. Reducing agents with weak strength of interaction with the catalyst surface, such as hydrocarbons, show poorer catalytic performance than reducing agents with a higher strength of interaction, such as alcohols. This is attributed to the greater ability of oxygenated species to compete with water in terms of surface interaction with the catalyst surface, hence reducing the inhibiting effect of water molecules blocking catalyst sites. The results support the observations of earlier work in that the light off-temperature and maximum NOx conversion and temperature at which that occurs are sensitive to the reducing agent present during reaction, and the proposal that improved catalyst performance is caused by increased adsorption strength of the reducing agent, relative to water, at the catalyst surface. Importantly, the NMR relaxation time analysis approach to characterising the strength of adsorption more readily describes the trends in catalytic behaviour than does a straightforward consideration of the polarity (i.e., relative permittivity) of the reducing agents studied here. In summary, this paper describes a simple approach to characterising the interaction energy of water and reducing agent so as to aid the selection of reducing agent and catalyst to be used in SCR conversions.

AB - The selective catalytic reduction (SCR) of NOx in the presence of different reducing agents over Ag/Al2O3 prepared by wet impregnation was investigated by probing catalyst activity and using NMR relaxation time analysis to probe the strength of surface interaction of the various reducing agent species and water. The results reveal that the strength of surface interaction of the reducing agent relative to water, the latter present in engine exhausts as a fuel combustion product and, in addition, produced during the SCR reaction, plays an important role in determining catalyst performance. Reducing agents with weak strength of interaction with the catalyst surface, such as hydrocarbons, show poorer catalytic performance than reducing agents with a higher strength of interaction, such as alcohols. This is attributed to the greater ability of oxygenated species to compete with water in terms of surface interaction with the catalyst surface, hence reducing the inhibiting effect of water molecules blocking catalyst sites. The results support the observations of earlier work in that the light off-temperature and maximum NOx conversion and temperature at which that occurs are sensitive to the reducing agent present during reaction, and the proposal that improved catalyst performance is caused by increased adsorption strength of the reducing agent, relative to water, at the catalyst surface. Importantly, the NMR relaxation time analysis approach to characterising the strength of adsorption more readily describes the trends in catalytic behaviour than does a straightforward consideration of the polarity (i.e., relative permittivity) of the reducing agents studied here. In summary, this paper describes a simple approach to characterising the interaction energy of water and reducing agent so as to aid the selection of reducing agent and catalyst to be used in SCR conversions.

U2 - 10.1039/c5cy01508a

DO - 10.1039/c5cy01508a

M3 - Article

VL - 6

SP - 1661

EP - 1666

JO - CATALYSIS SCIENCE & TECHNOLOGY

JF - CATALYSIS SCIENCE & TECHNOLOGY

SN - 2044-4753

IS - 6

ER -