Acidic Zirconia Materials for Durable NH3-SCR deNOx Catalysts

Verdier, Stéphane; Rohart, E.; Bradshaw, Heather; Harris, Deborah; Bichon, Philippe; Delahay, Gérard

doi:10.4271/2008-01-1022

Cited by 19 publications

(15 citation statements)

References 11 publications

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“…Indeed, the regeneration of the DPF leads to severe exotherms and the usual vanadium based SCR catalysts are not suitable due to possible sublimation of the oxide. As a consequence, new catalyst formulations have been developed, including Fe or Cu exchanged zeolites [31] and acidic oxide-based materials [32]. These formulations need to be firstly evaluated as powdered prototypes, i.e., only a few grams are commonly available.…”

Section: Introductionmentioning

confidence: 99%

Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

et al. 2015

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Abstract:The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literature, mainly because of its high potential to remediate the pollution of diesel exhaust gases. The implementation of the NH3-SCR process into passenger cars requires the use of an ammonia precursor, provided by a urea aqueous solution in the conventional process. Although the thermal decomposition and hydrolysis mechanisms of urea are well documented in the literature, the influence of the direct use of urea on the NOx reduction over SCR catalysts may be problematic. With the aim to evaluate prototype powdered catalysts, a specific synthetic gas bench adjusted to powdered material was developed, allowing the use of NH3 or urea as reductant for direct comparison. The design of the experimental setup allows vaporization of liquid urea at 200 °C under 10 bar using an HPLC pump and a micro injector of 50 μm diameter. This work presents the experimental setup of the catalytic test and some remarkable catalytic results towards further development of new catalytic formulations specifically dedicated to urea-SCR. Indeed, a possible divergence in terms of DeNOx efficiency is evidenced depending on the nature of the reductant, NH3 or urea solution. Particularly, the evaluated catalyst may not allow an optimal NOx conversion because of a lack in ammonia availability when the urea residence time is shortened. This is attributed to insufficient activity of isocyanic acid (HNCO) hydrolysis, OPEN ACCESSCatalysts 2015, 5 1536 which can be improved by addition upstream of an active solid for the hydrolysis reaction such as ZrO2. Thus, this µ-scale synthetic gas bench adjusted to powdered materials enables the specific behaviour of urea use for NOx reduction to be demonstrated.

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Section: Introductionmentioning

confidence: 99%

Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

et al. 2015

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“…They are currently investigating this. New zeolite formulations are being developed for low temperature deNOx without copper (19), and new catalyst families based on acidic zirconia are also emerging (25).…”

Section: Selective Catalytic Reductionmentioning

confidence: 99%

Diesel Emission Control in Review

Johnson

2008

SAE Int. J. Fuels Lubr.

206

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This summary covers representative developments from 2008 in diesel regulations, engine technology, and NOx, particulate matter (PM), and hydrocarbon (HC) control. Europe is finalizing the Euro VI heavy-duty (HD) regulations for 2013 with the intent of technologically harmonizing with the US. A new particle number standard will be adopted. California is considering tightening the light-duty fleet average to US Tier 2 Bin 2 levels, and CO 2 mandates are emerging in Europe for LD, and in the US for all vehicles. LD engine technology is focused on downsizing to deliver lower CO 2 emissions, enabled by advances in boost and EGR (exhaust gas recirculation). Emerging concepts are shown for attaining Bin 2 emission levels. HD engines will make deNOx systems optional for even the tightest NOx standards, but deNOx systems enable much lower fuel consumption levels and will likely be used. NOx control is centered on SCR (selective catalytic reduction) for diverse applications. Focus is on cold operation, system optimization, and catalyst durability. LNT (lean NOx trap) performance is advancing and precious metal cost content is decreasing. Desulfation is enhanced, and new compositions are emerging based on alumina and ceria. LNCs (lean NOx catalysts or HC-SCR) developments are updated. Diesel particulate filter (DPF) technology is in a state of optimization and cost reduction. New DPF regeneration strategies are described as well as the new learnings on the fundamentals of soot/catalyst interaction and the impact of DPF pore structure. Finally an update on diesel oxidation catalysts (DOCs) is provided showing potential solutions for advanced combustion strategies.

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“…In recent years, the de-NOx performance and durability of Cuzeolite catalysts having superior low temperature activity have been improved in many studies [16][17][18][19][20][21]. Moreover, the effects of additives on the surface acidity and structural strength have been researched [22][23][24].…”

Section: Introductionmentioning

confidence: 99%