Advanced Urea SCR Catalysts for Automotive Applications

Gieshoff, J.; Pfeifer, Marcus; Schäfer-Sindlinger, A.; Spurk, Paul; Garr, G.; Leprince, Thierry; Crocker, Mark

doi:10.4271/2001-01-0514

Cited by 42 publications

(23 citation statements)

References 8 publications

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“…This can be extremely important when used in conjunction with self cleaning diesel particulate filters. Recently developed iron and copper exchanged zeolite urea SCRs have been developed with approximately equal performance to that of vanadium urea-SCRs if the fraction of the NO 2 is 20% to 50% of the total NOx (Gieshoff, et al, 2001).…”

Section: Selective Catalytic Reduction (Scr)mentioning

confidence: 99%

Combustion and emissions characteristics of compression-ignition engine using dual ammonia-diesel fuel

Reiter

Kong

2011

Fuel

568

132

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Section: Selective Catalytic Reduction (Scr)mentioning

confidence: 99%

Combustion and emissions characteristics of compression-ignition engine using dual ammonia-diesel fuel

Reiter

Kong

2011

Fuel

568

132

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“…CoO-Nb 2 O 5 -SiO 2 was prepared using a sol-gel method [14], employing Co(NO 3 ) 2 .6H 2 O, Nb(OEt) 5 and Si(OEt) 4 as precursors. Sol-gel CoO-SiO 2 was similarly prepared but with omission of the niobium compound.…”

Section: Catalyst Preparationmentioning

confidence: 99%

“…Additionally, the use of an oxidation catalyst extends the useful range of operation of monolithic vanadia-based SCR catalysts to temperatures as low as ca. 220 °C (for low sulfur applications) [5]. At temperatures above 350 °C the positive effect of NO 2 on the SCR reaction rate largely disappears [2].…”

Section: Introductionmentioning

confidence: 99%

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Development of Nitric Oxide Oxidation Catalysts for the Fast SCR Reaction

Crocker

2005

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This study was undertaken in order to assess the potential for oxidizing NO to NO 2 in flue gas environments, with the aim of promoting the so-called fast SCR reaction. In principle this can result in improved SCR kinetics and reduced SCR catalyst volumes. Prior to commencing experimental work, a literature study was undertaken to identify candidate catalysts for screening. Selection criteria comprised (i) proven (or likely) activity for NO oxidation, (ii) low activity for SO 2 oxidation (where data were available), and (iii) inexpensive component materials. Catalysts identified included supported base metal oxides, supported and unsupported mixed metal oxides, and metal ion exchanged ZSM-5 (Fe, Co, Cu). For comparison purposes, several low loaded Pt catalysts (0.5 wt% Pt) were also included in the study.Screening experiments were conducted using a synthetic feed gas representative of flue gas from coal-fired utility boilers:.5%, balance = N 2 ; T = 275-375 °C. Studies conducted in the absence of SO 2 revealed a number of supported and unsupported metal oxides to be extremely active for NO oxidation to NO 2 . These included known catalysts (Co 3 O 4 /SiO 2 , FeMnO 3 , Cr 2 O 3 /TiO 2 ), as well as a new one identified in this work, CrFeO x /SiO 2 . However, in the presence of SO 2 , all the catalysts tested were found to be severely deactivated with respect to NO oxidation. Of these, Co 3 O 4 /SiO 2 , Pt/ZSM-5 and Pt/CeO 2 showed the highest activity for NO oxidation in the presence of SO 2 (based on peak NO conversions to NO 2 ), although in no cases did the NO conversion exceed 7%.Reactor studies indicate there are two components to SO 2 -induced deactivation of Co 3 O 4 /SiO 2 , corresponding to an irreversible deactivation due to sulfation of the surface of the Co 3 O 4 phase, together with a reversible inhibition due to competitive adsorption of SO 2 with NO on the catalyst. In an effort to minimize the deactivating effect of SO 2 on Co 3 O 4 /SiO 2 , two synthetic approaches were briefly examined. These consisted of (i) the incorporation of highly dispersed Co(II) ions in silica, as a non-sulfating matrix, via the sol-gel preparation of CoO-SiO 2 ; and (ii) the sol-gel preparation of a mixed metal oxide, CoO-Nb 2 O 5 -SiO 2 , with the aim of exploiting the acidity of the niobium oxide to minimize SO 2 adsorption. While both catalysts showed almost no activity for NO oxidation in the absence of SO 2 , when SO 2 was present low activity was observed, indicating that SO 2 acts as a promoter for NO oxidation over these materials.The kinetics of NO oxidation over Co 3 O 4 /SiO 2 , Pt/SiO 2 and Pt/CeO 2 were also examined. Co 3 O 4 /SiO 2 was found to exhibit a higher apparent activation energy for NO oxidation than the Pt catalysts, while the combined reaction order in NO and O 2 for the three catalysts was very close to one. CO 2 was found to have no effect on the kinetics of NO oxidation over these catalysts. The presence of H 2 O caused a decrease in NO conversion for both Co 3 O 4 /SiO 2 and Pt/CeO ...

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“…Catalytic technology of after-treatment systems consists mainly of NO x direct decomposition (NDD) (Tadao et al, 2003), lean NO x traps (LNTs) (Tabata et al, 1995;Gregory et al, 1999), and selective catalytic reduction (SCR) (Gieshoff et al, 2001). Compared with NDD and SCR, LNTs attract more interest because of their higher NO x conversion efficiency.…”

Section: Introductionmentioning

confidence: 99%

Effect of rich air/fuel ratio and temperature on NO x desorption of lean NO x trap

Liu

Zhang

et al. 2013

J. Zhejiang Univ. Sci. A

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An experimental and model-based study of the effect of rich air/fuel ratios (AFRs) and temperature on the NO x slip of a lean NO x trap (LNT) was conducted in a lean-burn gasoline engine with an LNT after-treatment system. The emissions of the engine test bench and the inlet temperature of the LNT were used as the major inlet boundary conditions of the LNT. The engine periodically operated between a constant lean AFR of 23 with alterable rich AFRs of 10, 11, 12, 13, and 14. A decrease in the rich AFR of the engine strengthened the desorption atmosphere in the LNT, an effect closely related to the number of reductants, and further heightened the NO x desorption of the LNT, but with a penalty in fuel consumption. To eliminate that penalty, the inlet boundary conditions of the LNT were varied by adjusting the inlet temperature within a range between 200 °C and 400 °C. An increase in inlet temperature heightened the NO x desorption of the LNT, and a NO x breakthrough occurred after the inlet temperature exceeded 390 °C. To control NO x breakthrough, the inlet temperature can be adjusted to offset the strong desorption atmosphere in the LNT commonly created by a rich AFR.

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Advanced Urea SCR Catalysts for Automotive Applications

Cited by 42 publications

References 8 publications

Combustion and emissions characteristics of compression-ignition engine using dual ammonia-diesel fuel

Combustion and emissions characteristics of compression-ignition engine using dual ammonia-diesel fuel

Development of Nitric Oxide Oxidation Catalysts for the Fast SCR Reaction

Effect of rich air/fuel ratio and temperature on NO x desorption of lean NO x trap

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