Combined catalytic systems for enhanced low-temperature NOx abatementCatalysis Today

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Authors
A.Yu. Stakheev, A.I. Mytareva, D.A. Bokarev, G.N. Baeva, D.S. Krivoruchenko, A.L. Kustov, M. Grill, J.R. Thøgersen
Year
2015
DOI
10.1016/j.cattod.2015.05.023
Subject
Chemistry (all) / Catalysis

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Text

Please cit

Catal. Tod

ARTICLE IN PRESSG ModelCATTOD-9635; No. of Pages 7

Catalysis Today xxx (2015) xxx–xxx

Contents lists available at ScienceDirect

Catalysis Today j our na l ho me page: www.elsev ier .com/ locate /ca t tod

Combin -te abatem

A.Yu. Sta a, D

A.L. Kust a Zelinsky Instit b Haldor Topsø a r t i c l

Article history:

Received 24 Ja

Received in re

Accepted 21 M

Available onlin

Keywords:

Selective catalytic reduction

Low-temperature SCR

Fast SCR

Fe-Beta

Ceria–zirconia bine –Ce/C

DeNO was r and selectivities far above performances of the individual components. Significant improvement was observed within 150–250 ◦C temperature range. Detailed study of a possible origin of the synergistic effect suggested that the improvement of NH3-DeNOx activity can be attributed to the bifunctional mechanism comprising two main stages: 2NO + O2 ↔ 2NO2 over RedOx component (1) 1. Introdu

Selective (NH3-SCR) of NOx emi (power plan using cataly

Beta or Cu-B

NOx conver slip problem upswings. M of metal ox lic catalysts catalysts w high activit ∗ Correspon

E-mail add http://dx.doi.o 0920-5861/© e this article in press as: A.Yu. Stakheev, et al., Combined catalytic systems for enhanced low-temperature NOx abatement, ay (2015), http://dx.doi.org/10.1016/j.cattod.2015.05.023

NO + NO2 + 2NH3 → 2N2 + 3H2O over zeolite component (2)

Remarkably, the synergistic effect was attained by mixing RedOx component with H-Beta possessing negligible activity in Standard SCR but active in Fast SCR. Nevertheless, further research is required for revealing overall reaction network and understanding reaction mechanism responsible for the observed synergy. © 2015 Elsevier B.V. All rights reserved. ction catalytic reduction of nitrogen oxides by ammonia is of theoretical and practical interest for abatement ssion from automotive (diesel engines) and stationary ts) sources [1,2]. Recently, NH3-SCR can be achieved by tic systems based on Fe-Beta or Cu-Beta. However, Feeta zeolites have two main drawbacks: (1) insufficient sion at “cold-start” condition (150–250 ◦C) and (2) NH3due to incomplete conversion or exhaust temperature any studies have been devoted to the development ide (Mn, Ce, Cu and Fe), supported metals, or bimetalfor low-temperature SCR applications [3–5]. Dual-bed ere also considered as promising systems due to their y within wide temperature range [6]. ding author. Tel.: +7 499 137 2944; fax: +7 499 135 5328. ress: st@ioc.ac.ru (A.Yu. Stakheev).

Another promising solution can be provided by combined catalysts (CombiCats) comprising SCR and RedOx functions. This approach was firstly applied by Misono et al. [7,8]. It was shown that physical mixing of Mn2O3 with M-zeolites results in the activity improvement. They proposed a bifunctional mechanism of C3H6SCR over the physical mixture of Mn2O3 or CeO2 and M-zeolite (M – various metals). The observed activity improvement was explained as follows: Mn2O3 oxidizes NO to NO2 and M-zeolite is responsible for the reaction between NO2 and propylene and the decomposition of intermediates to N2. Our recent study [9] indicated that such bifunctional mechanism also can be successfully applied in

NH3-SCR process. The basic idea was based on the fact discovered by Kasaoka et al. [10] that the NH3-SCR of NO/NO2 mixtures (Eq. (1)) is much faster than the NH3-SCR of NO alone (Eq. (2)):

NO + NO2 + 2NH3 → 2N2 + 3H2O–FastSCR (1) 4NH3 + 4NO + O2 → 4N2 + 6H2O–StandardSCR (2)

Our study demonstrated [9] that high NOx SCR performance at Treact. < 250 ◦C can be provided by the combined catalysts rg/10.1016/j.cattod.2015.05.023 2015 Elsevier B.V. All rights reserved.ed catalytic systems for enhanced low ent kheeva,∗, A.I. Mytarevaa, D.A. Bokareva, G.N. Baeva ovb, M. Grill b, J.R. Thøgersenb ute of Organic Chemistry, Leninsky Pr. 47, Moscow 119991, Russia e A/S, Nymøllevej 55, 2800 Lyngby, Denmark e i n f o nuary 2015 vised form 2 May 2015 ay 2015 e xxx a b s t r a c t

NH3-DeNOx performances of the com

RedOx component (CeO2–ZrO2 or Mn were studied in details. By comparing nents a pronounced synergistic effect mperature NOx .S. Krivoruchenkoa, d catalysts (CombiCats) prepared by mechanical mixing of eO2–ZrO2) and zeolite component (Fe-Beta, H-Beta, USY, etc.) x performances of the CombiCats and their individual compoevealed, as evidenced by the improvement of DeNOx activities

Please cit c sys

Catal. Tod

ARTICLE IN PRESSG ModelCATTOD-9635; No. of Pages 7 2 A.Yu. Stakheev et al. / Catalysis Today xxx (2015) xxx–xxx comprising a RedOx component (possessing high activity in NO oxidation) and zeolite component (highly effective in the Fast SCR).

For [CeO2–ZrO2 + Fe-Beta] and [Mn/CeO2–ZrO2 + Fe-Beta] compositions a pronounced synergistic effect was observed and the catalytic activity of t vidual com

CombiCats prising (1) N

SCR reactio 2NO + O2 ↔

NO + NO2 +

Salazar moting. Inte of Fe-ZSM-5 oxides were with NH3. E that the bifu mation follo proof is diffi

In this s bifunctiona was to disc the zeolite a series of ple was us based on th both in Sta recent stud is sufficient

Standard SC good agreem reducing th mize Standa

Fast SCR ac overall syne and amorph

Fast SCR, al

SCR reactio

CeO2–Zr to NO2 oxid 2. Experim 2.1. Catalys

Parent (Si/Al ≈ 40) converted i 4 h. SiO2–A

Beta (Si/Al sis describe

SiO2–Al2O3

Chemica inductively

OES) on an

Fe-Beta, H-B < 0.002 wt%

Commer used as the 8 wt% Mn a an aqueous

Aldrich, ≥9 99.999%) fo at 550 ◦C for 4 h in an airflow. Parent and modified samples will be labeled Ce–Zr and Mn–Ce/Ce–Zr, respectively.

Two series of the composite catalysts was prepared by mixing Ce–Zr or Mn–Ce/Ce–Zr with Fe-Beta, H-Beta, “Fe-free” Beta, nd S imat d in riate mpo

Z re e/Ce talys mor gate n a H ed in . pera out reac ced t ment cool ◦C in upo tecto eth ldric talyt act mpo reac m N 2. To com ts in ) was 00 h