The Use of Palladium in Advanced Catalysts

Brisley, R. J.; Chandler, G. R.; Jones, Hannah; Anderson, Paul; Shady, P. J.

doi:10.4271/950259

Cited by 32 publications

(2 citation statements)

References 5 publications

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“…Simply higher Pd loadings do not improve catalytic performances beyond a certain concentration of such precious metals [36][37][38] since strong CO and Pd interactions can occur making desorption of CO from Pd a rate-limiting step [39]. Rapid rates of oxidation are also observed on catalyst exhibiting a high density of Pd active sites, leading to an insufficient concentration of CO, HC and H 2 which are required for NO x reduction [40]. In addition, high Pd loading favors high-temperature sintering besides also increasing the manufacturing cost of such catalysts.…”

Section: General Assessmentmentioning

confidence: 99%

Evaluating Different Strategies to Minimize cold-start Emissions from Gasoline Engines in steady-state and Transient Regimes

Nandi¹,

Chaillou²,

Dujardin³

et al. 2022

Top Catal

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Exhaust car emissions increase significantly at particular gasoline engine driving cycle such as cold-start when the three-way catalyst has not reached its light-off temperature. More efficient technologies are needed to reduce these extra emissions. This study focuses on comparing two strategies to lower cold-start pollutants on a commercial monolithic catalyst: (i) a high content of PGMs (Pd and Rh) loading with a variable concentration distribution along the catalyst, called zone-coating, was investigated in order to take advantages of an in situ pre-heating due to exothermic oxidation processes. And (ii) the use of external device for heating the monolith with the aim to shorten the laps of time to reach the required temperature for their conversion. Both approaches were compared below 300 °C in terms of NO, CO and hydrocarbons conversions as well as N 2 O formation with respect to homogeneously wash-coated catalyst. For evaluation, complex exhaust gas compositions were considered at different steady-state air-to-fuel λ ratios and high frequency transient lean/rich regime to mimic real operation in gasoline engine exhaust.Results show that a pre-heating of the catalyst at 300 °C is necessary to avoid completely N 2 O formation from NO reduction with CO. Remarkably higher NO and CH 4 conversions were observed during transient regimes rather than steady-state lean, rich or stoichiometric conditions at 200 °C and 300 °C.

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Section: General Assessmentmentioning

confidence: 99%

Evaluating Different Strategies to Minimize cold-start Emissions from Gasoline Engines in steady-state and Transient Regimes

Nandi¹,

Chaillou²,

Dujardin³

et al. 2022

Top Catal

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“…By the correct use of promoters, particularly alkaline earths and lanthanide oxides, it was possible to modify the catalytic properties of palladium so it can function as a TWC, that is, catalyse reduction of NO x as well as oxidation of CO and HC (Summers et al 1989;Brisley et al 1995). This entails interplay between catalysis by the metal and its oxide, the presence of which can be controlled by close contact with cations that stabilize surface oxygen.…”

Section: (D) Three-way Catalystsmentioning

confidence: 99%

Controlling automotive exhaust emissions: successes and underlying science

Twigg

2005

Phil. Trans. R. Soc. A.

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Photochemical reactions of vehicle exhaust pollutants were responsible for photochemical smog in many cities during the 1960s and 1970s. Engine improvements helped, but additional measures were needed to achieve legislated emissions levels. First oxidation catalysts lowered hydrocarbon and carbon monoxide, and later nitrogen oxides were reduced to nitrogen in a two-stage process. By the 1980s, exhaust gas could be kept stoichiometric and hydrocarbons, carbon monoxide and nitrogen oxides were simultaneously converted over a single 'three-way catalyst'. Today, advanced three-way catalyst systems emissions are exceptionally low. NOx control from lean-burn engines demands an additional approach because NO cannot be dissociated under lean conditions. Current lean-burn gasoline engine NOx control involves forming a nitrate phase and periodically enriching the exhaust to reduce it to nitrogen, and this is being modified for use on diesel engines. Selective catalytic reduction with ammonia is an alternative that can be very efficient, but it requires ammonia or a compound from which it can be obtained. Diesel engines produce particulate matter, and, because of health concerns, filtration processes are being introduced to control these emissions. On heavy duty diesel engines the exhaust gas temperature is high enough for NO in the exhaust to be oxidised over a catalyst to NO2 that smoothly oxidises particulate material (PM) in the filter. Passenger cars operate at lower temperatures, and it is necessary to periodically burn the PM in air at high temperatures.

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