Rôles of catalytic oxidation in control of vehicle exhaust emissions

Twigg, M. V.

doi:10.1016/j.cattod.2006.06.044

Cited by 92 publications

(45 citation statements)

References 37 publications

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“…Although bicelles have been suggested as templating agents for the growth of nanomaterials, prior to our recent study 11 no successful examples had been reported, partially because of the difficulties in obtaining high yields of bicelles. 3,4 In an earlier study, 11 we investigated the synthesis of platinum materials to demonstrate the templating ability of bicelles, since platinum is technologically important for applications in sensing, 12,13 reduction of tailpipe emissions, [14][15][16] electrocatalytic energy conversion in proton exchange membrane (PEM) fuel cells, [17][18][19] and renewable energy production in artificial photosynthesis and water-splitting devices. 20,21 Our previous study primarily focused on the synthesis and structural characterizations of the platinum nanowheels obtained in the presence of bicelles.…”

Section: Introductionmentioning

confidence: 99%

Templated growth of platinum nanowheels using the inhomogeneous reaction environment of bicelles

Garcia

Song

Dorin

et al. 2011

Phys. Chem. Chem. Phys.

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Section: Introductionmentioning

confidence: 99%

Templated growth of platinum nanowheels using the inhomogeneous reaction environment of bicelles

Garcia

Song

Dorin

et al. 2011

Phys. Chem. Chem. Phys.

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“…[1] Kinetic models for this reaction have been reported [2] with structural inferences based on Rh(111). Surface-science studies have provided elegant descriptions of surface oxidation (by O 2 ).…”

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confidence: 98%

Rhodium Dispersion during NO/CO Conversions

et al. 2007

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The catalyzed reaction between NO and CO for NO x removal is a key component of the role of rhodium in automotive exhaust catalysts.[1] Kinetic models for this reaction have been reported [2] with structural inferences based on Rh(111). Surface-science studies have provided elegant descriptions of surface oxidation (by O 2 ).[3] However, the mean nuclearity of the metal on Rh/Al 2 O 3 during the reduction of NO by H 2 varies with gas partial pressures and temperature.[4] Hence, an assumption of an invariant core catalyst may be invalid for highly dispersed catalysts. Indeed, combinations of CO and NO at low temperatures (< 473 K) aggressively corrode nanoparticulate rhodium to release Rh(CO) 2 centers, [5] which are mononuclear [6] and whose generation has also been monitored kinetically. [7] Our previous experiments showed that 5 wt % Rh/Al 2 O 3 , prepared from rhodium trichloride, underwent structural changes during a thermal ramp under a 1:1 mixture of 5 % CO/He and 5 % NO/He.[5] At room temperature, the predominant IR bands for the adsorbates were owing to Rh I (CO) 2 units and the mean Rh-Rh coordination number was found to be approximately 3. By 473 K, the intensity of the n(CO) as IR band (as = asymmetric) owing to Rh(CO) 2 centers was just past its maximum.In this study, the simultaneous monitoring of catalysts by diffuse reflectance and time dependence of any structural changes was monitored at 473 K on a prereduced sample, with the sequence starting under CO/He. The NO and CO streams were switched alternatively every 10 seconds for a total of nine switches; little CO 2 or N 2 O were formed during this sequence (Figure 1). The initial Rh-Rh coordination number (7.3) was reduced to approximately 4 with the second NO pulse and oscillated between values of 4 and 5 thereafter; these small changes were slower than the pulsing interval. The simultaneous monitoring of the catalysts by diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that bridging (1866 cm À1 ) and terminal (2059 cm À1 ) CO bands that are typical of sites on metallic rhodium were essentially lost after 10 s of NO exposure; these were replaced by absorptions owing to the Rh(CO) 2 unit (2096 and 2031 cm À1 ) upon exposure to CO. After the second cycle, intensity patterns following the gas switches became established with the two IR bands of the geminal dicarbonyl being formed during CO exposure, and being rapidly lost after switching to NO. A new IR band at 1931 cm À1 then emerged, which can be assigned to a linear rhodium nitrosyl on an oxidized rhodium of some form. [8,9] In the previous temperature-ramp study, [5] significant NO conversion was evident at 573 K, the Rh(CO) 2 unit was not observed, and the steady-state Rh-Rh nuclearity had begun to increase. In the isothermal gas-cycling experiment at 573 K, the reduction in the Rh-Rh coordination number was even greater than at 473 K, falling to approximately 2.8 after the second NO pulse and then tracking the switching sequence oscillating between approximately 2.8 (...

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“…The percentage 13) investigated the reaction of NO 2 and OH radicals with PAHs adsorbed on diesel exhaust particles by exposing the particles to gaseous NO 2 at 8.0 × 10 13 molecules/cm 3 (3.2 ppm) in a flow tube; they found that B[a]P was the most reactive PAH, with degradation of 25 ± 7% over 1800 s. The other PAHs, such as Phen and B[a]A, had degradation yields of 10% and 14%, respectively. Oxidation catalysts that are known to increase NO 2 emissions [14][15][16] were attached to the test vehicles. Therefore, the low recovery rates of B[a]P-d observed from HD-1 and HD-2 are likely to have been caused by oxidation by substances in the exhausts, such as NO 2 , during collection.…”

Section: Emission Characteristics Of Pahsmentioning

confidence: 99%

Emission Characteristics and Cancer Risks of Polycyclic Aromatic Hydrocarbon Emissions from Diesel-fueled Vehicles Complying with Recent Regulations

Kashiwakura

Sakamoto

2010

JOURNAL OF HEALTH SCIENCE

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Polycyclic aromatic hydrocarbon (PAH) emissions from diesel vehicles have been reduced by recent regulations further dropping the permissible levels of regulated substances. We analyzed emissions of 13 PAHs from cold-or hot-start test cycles in three diesel vehicles complying with these stringent regulations, and we estimated cancer risk in terms of toxic equivalency factors (TEFs). Two vehicles were equipped with oxidation catalysts and one with a urea-selective catalytic reduction (SCR) system. Most PAH emissions were lower from the compliant vehicles than from other diesel vehicles with no aftertreatment devices. For the three vehicles, naphthalene (Naph) was emitted at the highest rate (2.92-376 µg/km); by mass it constituted 51.1-84.8% (mean 73.0%, S.D. ± 12.2%) of all PAH emissions. However, in the SCR system, Naph emissions probably decomposed during collection, because the percentage recoveries of surrogate were low, suggesting the presence of specific reactive substances in the SCR system exhaust.

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Rôles of catalytic oxidation in control of vehicle exhaust emissions

Cited by 92 publications

References 37 publications

Templated growth of platinum nanowheels using the inhomogeneous reaction environment of bicelles

Templated growth of platinum nanowheels using the inhomogeneous reaction environment of bicelles

Rhodium Dispersion during NO/CO Conversions

Emission Characteristics and Cancer Risks of Polycyclic Aromatic Hydrocarbon Emissions from Diesel-fueled Vehicles Complying with Recent Regulations

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