Catalytic reduction of nitrogen oxides in diesel exhaust gas

Engler, Bernd; Leyrer, J.; Lox, E.S.; Ostgathe, K.

doi:10.1016/s0167-2991(06)81456-4

Cited by 30 publications

(10 citation statements)

References 14 publications

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“…The complex chemical environments typical of an automotive exhaust stream have generally only been evaluated in more applied screening or durability studies [6,11,12,32,[36][37][38][39][40]. Virtually all mechanistic studies to date related to active lean-NOx catalysis have involved simple, high purity feed-gas mixtures (often including only a single hydrocarbon reductant).…”

Section: Low Na Pt/hto:si Catalystsmentioning

confidence: 99%

“…Virtually all mechanistic studies to date related to active lean-NOx catalysis have involved simple, high purity feed-gas mixtures (often including only a single hydrocarbon reductant). These studies have resulted in several postulated mechanisms for lean-burn NOx reduction that involve: 1) oxidation of NO to NO 2 , which then reacts with hydrocarbons [41][42][43]; 2) formation of a highly reactive, partially oxidized hydrocarbon intermediate [7,36,44,45]; 3) formation of an intermediate species containing both carbon and nitrogen [41,[46][47][48][49]; and 4) reduction of the metal surface followed by NO dissociation on the metal [9,10,30,42,43,50]. Substantial evidence has shown the existence of unique, hydrocarbon-dependent NOx reduction mechanisms involving various contributions of the catalyst support and/or the Pt particles [42,43,50].…”

Section: Low Na Pt/hto:si Catalystsmentioning

confidence: 99%

“…Thus, although CO can play important roles in the NOx reduction mechanism in net neutral or net reducing exhaust environments, it is unlikely that CO significantly participates in the overall NOx reduction mechanism in oxidizing exhaust environments, as long as other hydrocarbons are present in reasonable quantities [6,31,35,36]. This is illustrated in Figure 1 by the fact that the conversion of CO is nearly 100% complete by 150°C, well before any significant NOx conversion is observed.…”

Section: Low Na Pt/hto:si Catalystsmentioning

confidence: 99%

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Preparation Effects on the Performance of Silica-Doped Hydrous Titanium Oxide (HTO:Si)-Supported Pt Catalysts for Lean-Burn NOx Reduction by Hydrocarbons

Gardner¹,

McLaughlin²,

Mowery³

et al. 2002

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This report describes the development of bulk hydrous titanium oxide (HTO)-and silicadoped hydrous titanium oxide (HTO:Si)-supported Pt catalysts for lean-burn NOx catalyst applications. The effects of various preparation methods, including both anion and cation exchange, and specifically the effect of Na content on the performance of Pt/HTO:Si catalysts, were evaluated. Pt/HTO:Si catalysts with low Na content (< 0.5 wt.%) were found to be very active for NOx reduction in simulated lean-burn exhaust environments utilizing propylene as the major reductant species. The activity and performance of these low Na Pt/HTO:Si catalysts were comparable to supported Pt catalysts prepared using conventional oxide or zeolite supports. In ramp down temperature profile test conditions, Pt/HTO:Si catalysts with Na contents in the range of 3-5 wt.% showed a wide temperature window of appreciable NOx conversion relative to low Na Pt/HTO:Si catalysts. Full reactant species analysis using both ramp up and isothermal test conditions with the high Na Pt/HTO:Si catalysts, as well as diffuse reflectance FTIR studies, showed that this phenomenon was related to transient NOx storage effects associated with NaNO 2 /NaNO 3 formation. These nitrite/nitrate species were found to decompose and release NOx at temperatures above 300°C in the reaction environment (ramp up profile). A separate NOx uptake experiment at 275°C in NO/N 2 /O 2 showed that the Na phase was inefficiently utilized for NOx storage. Steady state tests showed that the effect of increased Na content was to delay NOx light-off and to decrease the maximum NOx conversion. Similar results were observed for high K Pt/HTO:Si catalysts, and the effects of high alkali content were found to be independent of the sample preparation technique. Catalyst characterization (BET surface area, H 2 chemisorption, and transmission electron microscopy) was performed to elucidate differences between the HTO-and HTO:Sisupported Pt catalysts and conventional oxide-or zeolite-supported Pt catalysts.4

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Section: Low Na Pt/hto:si Catalystsmentioning

confidence: 99%

Section: Low Na Pt/hto:si Catalystsmentioning

confidence: 99%

Section: Low Na Pt/hto:si Catalystsmentioning

confidence: 99%

See 1 more Smart Citation

Preparation Effects on the Performance of Silica-Doped Hydrous Titanium Oxide (HTO:Si)-Supported Pt Catalysts for Lean-Burn NOx Reduction by Hydrocarbons

Gardner¹,

McLaughlin²,

Mowery³

et al. 2002

View full text Add to dashboard Cite

show abstract

“…In the last few years, several scientific programs have been investigating the possibility of improving such reactions. It has been shown, particularly in Japan, that Schematic diagram of various options for catalyst preheating (31) loo 1 Speed (FTP-75) selective catalytic reduction of NO can be obtained with hydrocarbons on copper ion-exchanged zeolites or on some other noble-metal or nonnoble-metal catalysts (34)(35)(36). The problem is that with most of the catalyst presently available, the reactions occur at too high temperature and under too low gas-space-velocities (ratio between gas flow and catalyst volume).…”

Section: Fig 12mentioning

confidence: 99%

Catalytic automotive exhaust gas depollution: Present status and new trends

Prigent

1996

Bulletin des Soc Chimique

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Journ6e de Contact en Catalyse de la Communauth Franpaise de Belgique : "Catalyse par les metaux" le 7 dbcembre 1995, Bruxelles ABSTRACTA review is made of the various types of exhaust gas aftertreatment systems presently used on most vehicles to reduce pdlutant emissions. The systems are differentiated by their mode of action, according to the engine type to be depolluted (2-strokes, 4-strokes, diesel or spark-ignition), and by their type of make-up. The major developmentsforeseen in the future, in view of compliance with the new legislations, are described. Means enabling some prototype vehicles with internal combustion engines to emit pollutant quantities really close to zero, such as electric cars, are described.

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“…The employment of noble catalysts, however, is limited due to their scarcity, high cost (Engler et al, 1995), toxicity (Klaasen, 1996;Palacios et al, 2000), and inability to function in a lean-burn engine exhaust (Subbiah et al, 2003). As of July 15, 2005, the prices per ounce of platinum, palladium, and rhodium were $857, $182, and $2,005, respectively (www.kitco.com).…”

Section: Introductionmentioning

confidence: 99%

Removal of Nitrogen Oxides Using Nanosized Catalysts Prepared by Dry Mechanical Coating Technique

Coowanitwong

Cai

et al. 2007

Environmental Engineering Science

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Nitrogen oxides (NO x ) are the key air pollutants emitted by mobile and stationary sources, and are a major cause of adverse health and environmental effects. One promising alternative material to conventional noble metal-based catalysts for NO x emission control is the group of transition metal oxides, in particular, CuO. In this study, well-dispersed CuO and CuO/Al 2 O 3 nanocatalysts coated onto durable Al 2 O 3 fiber substrates were assessed for NO conversion efficiency. The resultant composite materials had high surface area with good dispersion for enhanced NO conversion. Operating parameters, including nanocatalysts loading and temperature, were investigated for their effects on the catalytic performance for NO conversion. The experimental results showed that the activity of the catalysts is strongly related to the loading amount and the degree of dispersion of CuO nanoparticles. The binary CuO/Al 2 O 3 system yielded a higher NO conversion efficiency than the system consisting of CuO alone. Small amounts of Al 2 O 3 employed in the binary system resulted in better dispersion, and subsequently the achievement of higher NO conversion efficiency. The stability of the catalysts was demonstrated over a wide range of temperatures, and proved satisfactory for the harsh environment of the exhaust system. However, sintering and alloying effects that result in a decrease in surface area may potentially lower the catalytic activity at high temperatures.

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Catalytic reduction of nitrogen oxides in diesel exhaust gas

Cited by 30 publications

References 14 publications

Preparation Effects on the Performance of Silica-Doped Hydrous Titanium Oxide (HTO:Si)-Supported Pt Catalysts for Lean-Burn NOx Reduction by Hydrocarbons

Preparation Effects on the Performance of Silica-Doped Hydrous Titanium Oxide (HTO:Si)-Supported Pt Catalysts for Lean-Burn NOx Reduction by Hydrocarbons

Catalytic automotive exhaust gas depollution: Present status and new trends

Removal of Nitrogen Oxides Using Nanosized Catalysts Prepared by Dry Mechanical Coating Technique

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