Improved SCR Systems for Heavy Duty Applications

Gieshoff, J.; Schäfer-Sindlinger, A.; Spurk, Paul; Tillaart, J.A.A. van den; Garr, G.

doi:10.4271/2000-01-0189

Cited by 85 publications

(67 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…50% of the NO to NO 2 ; this, in turn, enables the SCR catalyst volume to be reduced. Studies with diesel engine exhaust have shown that by promoting the fast SCR reaction in this manner, SCR catalyst volumes can effectively be halved, while maintaining a given NO x conversion level (at typical diesel engine operating temperatures) [4]. 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.…”

Section: Introductionmentioning

confidence: 99%

“…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%

“…For example, in mobile applications the oxidation catalyst volume is typically set at ∼0.3 that of the SCR catalyst, which is itself set at ∼0.5 that of the volume required when no oxidation catalyst is used [4]. Assuming that the oxidation catalyst is not more than 50% more expensive to manufacture than the SCR catalyst, the combined oxidation/SCR catalyst system shows a cost saving relative to the SCR-only system of at least 27.5%.…”

Section: Introductionmentioning

confidence: 99%

“…For mobile applications, high activity platinum-based diesel oxidation catalysts are employed for NO oxidation [4,5]. However, such catalysts are unsuitable for applications in which high SO 2 concentrations are present due to their considerable activity for SO 2 oxidation.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Development of Nitric Oxide Oxidation Catalysts for the Fast SCR Reaction

Crocker

2005

View full text Add to dashboard Cite

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 ...

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Catalyst Preparationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Development of Nitric Oxide Oxidation Catalysts for the Fast SCR Reaction

Crocker

2005

View full text Add to dashboard Cite

show abstract

“…The heterogeneous chemical reactions taking place on the catalytic surface are also taken into account based on the Langmuir-Hinshelwood (LH) mechanism, while the NH 3 storage phenomena are adopted through the Dubinin-Radushkevich adsorption isotherm (Tsinoglou and Koltsakis, 2007). To evaluate the DeNO x performance, Gieshoff et al (2000) carried out studies and changed parameters such as the NH 3 /NO x and the NO 2 /NO x ratios over a V 2 O 5 catalyst. Also, in an effort to improve the NO x conversion efficiency, several investigations have been performed using parameters such as space velocity, the temperature of the SCR catalyst, and the volume of oxidation catalyst, at different raw NO x concentrations (Nam, 2007).…”

Section: Brazilian Journal Of Chemical Engineeringmentioning

confidence: 99%

SELECTIVE CATALYTIC REDUCTION (SCR) OF NO BY AMMONIA OVER V2O5/TiO2 CATALYST IN A CATALYTIC FILTER MEDIUM AND HONEYCOMB REACTOR: A KINETIC MODELING STUDY

Nahavandi

2015

Braz. J. Chem. Eng.

View full text Add to dashboard Cite

-The present study addresses a numerical modeling and simulation based on the available knowledge of SCR kinetics for prediction of NO conversion over a V 2 O 5 /TiO 2 catalyst through a catalytic filter medium and honeycomb reactor. After introducing the NH 3 -SCR system with specific operational criteria, a reactor model was developed to evaluate the effect of various operating parameters such as flue gas temperature, velocity, NH 3 /NO molar ratio, etc., on the SCR process. Computational investigations were performed based on the proposed model and optimum operational conditions were identified. Simulation results indicate that SCR performance is substantially under the effects of reactant concentration and operating temperature, so that the concentration of unreacted ammonia emitted from reactor discharge (ammonia slip) increases significantly at NH 3 /NO ratios of more than 1.14 and operating temperatures less than 360 ºC and 300 ºC, respectively, in the catalytic filter medium and honeycomb reactor. The results also show that there are three sections in NO conversion variation versus changing temperature and the required conversion with a maximum of almost 87% and low level of ammonia slip can be achieved at the NH 3 /NO ratio of 1 and temperature range of 240-360 ºC in both reactors.

show abstract