Silver/Alumina Catalyst for Selective Catalytic Reduction of NO<sub>x</sub>to N<sub>2</sub>by Hydrocarbons in Diesel Powered Vehicles

Lindfors, Lars-Eric; Eränen, Kari; Klingstedt, Fredrik; Murzin, Dmitry Yu.

doi:10.1023/b:toca.0000024349.28158.f3

Cited by 62 publications

(35 citation statements)

References 12 publications

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“…Since Miyadera et al [14,15] reported the high activity of SCR by ethanol over Ag/Al 2 O 3 , supported Ag catalysts have attracted much attention [16,17]. Supported Ag catalysts show essentially good performances in the HC-SCR and are thought to be one of the promising candidates for SCR systems.…”

Section: Introductionmentioning

confidence: 99%

“…For the Ag catalysts, two major ways of enhancing the HC-SCR activity have been proposed: (1) the use of oxygenated or higher hydrocarbons and (2) the cofeeding of H 2 into the HC-SCR atmosphere. The use of oxygenated hydrocarbons, such as ethanol, as a gas phase reductant also results in a similar promotion effect [16,17,20,21]. The use of higher hydrocarbons results in the enhancement of hydrocarbon conversion via surface oxygenated species, which acts as favorable reductants of adsorbed NO x on Ag catalysts [22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

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Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

et al. 2005

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The addition of hydrogen in the reaction atmosphere is effective in promoting the activity of Ag/alumina and Ag-zeolites on the selective reduction of NO by hydrocarbons (HC-SCR) at low temperatures. The increment of NO conversion over Ag-MFI corresponds to the periodic addition of hydrogen into C 3 H 8 -SCR conditions. The UV-VIS spectra of Ag-MFI have revealed that the addition of hydrogen results in the formation of Ag n d+ clusters due to partial reduction and agglomeration of Ag species . The coincidence of the formation of the Ag n d+ clusters and the increment of NO conversion suggests that Ag n d+ clusters are the highly active species for HC-SCR. From analysis by H 2 -TPR, UV-VIS, and EXAFS, the structure of Ag n d+ clusters on Ag-MFI is identified as being Ag 4 2+ on average. The formation of Ag clusters was strongly affected by the type of zeolites: The major Ag species are Ag + ions for MOR, Ag n d+ clusters for MFI and BEA, and relatively large metallic Ag m particles for Y. The sequence of Ag agglomeration (MOR < MFI < BEA < Y) is in accordance with the strength of the acid sites of zeolites. It can be expected that the interaction between the positive charge of Ag n d+ clusters and acid sites, i.e., the ion-exchange site of zeolites, stabilizes Ag n d+ clusters. The type of Ag species under HC-SCR conditions depends on the concentration of gas-phase oxidants (NO, O 2 ) and reductants (H 2 , HC), and also on the number and strength of the zeolite acid sites.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

et al. 2005

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“…Besides the SCR of NO x by NH 3 or urea as a reductant, the SCR of NO x by hydrocarbon (HC) as a reductant can be a possible method to the removal of NO x from diesel and lean-burn gasoline engines. In recent studies, relatively durable and inexpensive alumina-supported silver catalysts (Ag/Al 2 O 3 ) have been considered to be a promising candidate for practical usage in the HC-SCR of NO x [2][3][4][5][6][7][8]. In our research into the HC-SCR of NO x over Ag/ Al 2 O 3 , we found a novel enolic surface species on Ag/ Al 2 O 3 [9] and proposed a new mechanism to explain the high-level efficiency of the SCR of NO x by ethanol over Ag/Al 2 O 3 [7,9,10], as shown in Scheme 1.…”

Section: Introductionmentioning

confidence: 99%

Review of Ag/Al2O3-Reductant System in the Selective Catalytic Reduction of NO x

Zhang

et al. 2008

Catal Surv Asia

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Ag/Al 2 O 3 is a promising catalyst for the selective catalytic reduction (SCR) by hydrocarbons (HC) of NO x in both laboratory and diesel engine bench tests. New developments of the HC-SCR of NO x over a Ag/ Al 2 O 3 catalyst are reviewed, including the efficiencies and sulfur tolerances of different Ag/Al 2 O 3 -reductant systems for the SCR of NO x ; the low-temperature activity improvement of H 2 -assisted HC-SCR of NO x over Ag/ Al 2 O 3 ; and the application of a Ag/Al 2 O 3 -ethanol SCR system with a heavy-duty diesel engine. The discussions are focused on the reaction mechanisms of different Ag/ Al 2 O 3 -reductant systems and H 2 -assisted HC-SCR of NO x over Ag/Al 2 O 3 . A SO 2 -resistant surface structure in situ synthesized on Ag/Al 2 O 3 by using ethanol as a reductant is proposed based on the study of the sulfate formation. These results provide new insight into the design of a high-efficiency NO x reduction system. The diesel engine bench test results showed that a Ag/Al 2 O 3 -ethanol system is promising for catalytic cleaning of NO x in diesel exhaust.

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“…Among the various catalysts proposed for HC-SCR system, Ag/Al 2 O 3 was found to be the most active and potential catalytic system, as it reduces the NO x with hydrocarbons typical of diesel exhaust, and has received considerable attention [1][2][3][4]. Extensive studies have been reported on Ag/Al 2 O 3 catalysts for SCR of NO using different types of hydrocarbon reductant and the highest catalytic activity was achieved using long-chain paraffinÕs as reductant, which makes Ag/Al 2 O 3 a potential candidate for application in cleaning of diesel engine exhaust [5][6][7]. Furthermore NO x can be converted at much lower temperatures, usually encountered in diesel exhaust in presence of hydrogen in the exhaust gas, and several research groups observed such a significant improvement in the activity over Ag/Al 2 O 3 catalysts in the low temperature region [8][9][10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 98%

Influence of Al2O3 support on the activity of Ag/Al2O3 catalysts for SCR of NO with decane

et al. 2007

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The role of the Al 2 O 3 support on the activity of supported Ag catalyst towards the selective catalytic reduction (SCR) of NO with decane is elucidated. A series of Ag/Al 2 O 3 catalysts were prepared by impregnation method and characterized by N 2 pore size distribution, XRD, UV-Vis, in-situ FT-IR and acidity measurement by NH 3 and pyridine adsorption. The catalytic activity differences of Ag/Al 2 O 3 are correlated with different properties of Al 2 O 3 supports and the active Ag species formed. 4wt% Ag supported on sol-gel prepared Al 2 O 3 (Ag/Al 2 O 3 (SG), showed higher NO x conversion (65% at 400°C), compared with the respective catalysts made from commercial Al 2 O 3 (Ag/Al 2 O 3 (GB), Ag/Al 2 O 3 (ALO), ($26 and 7% at 400°C). The higher surface area, acidity and pore size distribution in sol-gel prepared Al 2 O 3 (SG) results in higher NO and hydrocarbon conversion. Based on the UV-vis characterization, the activity of NO reduction is correlated to the presence of Ag n d+ clusters and acidity of Al 2 O 3 support was found to be one of the important parameter in promoting the formation and stabilization of Ag n d+ clusters. Furthermore from pyridine adsorption results, presence of more number of Bronsted acid sites in Ag/Al 2 O 3 (SG) is confirmed, which could also contribute to low temperature hydrocarbon activation and improve NO conversion. In situ FT-IR measurements revealed the higher rate of -CN and -NCO intermediate species formation over 4wt% Ag/Al 2 O 3 (SG). We conclude that the physico-chemical properties of Al 2 O 3 play a crucial role in NO x conversion over Ag/Al 2 O 3 catalysts. Thus, the activity of the Ag/ Al 2 O 3 catalyst can be tailored by using a proper type of Al 2 O 3 support.

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Silver/Alumina Catalyst for Selective Catalytic Reduction of NO_xto N₂by Hydrocarbons in Diesel Powered Vehicles

Cited by 62 publications

References 12 publications

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

Review of Ag/Al2O3-Reductant System in the Selective Catalytic Reduction of NO x

Influence of Al2O3 support on the activity of Ag/Al2O3 catalysts for SCR of NO with decane

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Silver/Alumina Catalyst for Selective Catalytic Reduction of NOxto N2by Hydrocarbons in Diesel Powered Vehicles

Cited by 62 publications

References 12 publications

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

Review of Ag/Al2O3-Reductant System in the Selective Catalytic Reduction of NO x

Influence of Al2O3 support on the activity of Ag/Al2O3 catalysts for SCR of NO with decane

Contact Info

Product

Resources

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Silver/Alumina Catalyst for Selective Catalytic Reduction of NO_xto N₂by Hydrocarbons in Diesel Powered Vehicles