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Journal ArticleDOI

Characterization of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts with hydrothermal treatment for NH3-SCR of NOx in diesel exhaust

01 Jun 2013-Chemical Engineering Journal (Elsevier)-Vol. 225, Iss: 225, pp 323-330
TL;DR: In this paper, the microstructure of the zeolite supports, identity of copper species, acidity and reactant adsorption ability were investigated in detail using various characterization methods.
About: This article is published in Chemical Engineering Journal.The article was published on 2013-06-01. It has received 279 citations till now. The article focuses on the topics: Catalyst support & Selective catalytic reduction.
Citations
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Journal ArticleDOI
22 May 2019-Nature
TL;DR: A protocol for the electrochemical reduction of nitrogen to ammonia enables isotope-sensitive quantification of the ammonia produced and the identification and removal of contaminants, and should help to prevent false positives from appearing in the literature.
Abstract: The electrochemical synthesis of ammonia from nitrogen under mild conditions using renewable electricity is an attractive alternative1–4 to the energy-intensive Haber–Bosch process, which dominates industrial ammonia production. However, there are considerable scientific and technical challenges5,6 facing the electrochemical alternative, and most experimental studies reported so far have achieved only low selectivities and conversions. The amount of ammonia produced is usually so small that it cannot be firmly attributed to electrochemical nitrogen fixation7–9 rather than contamination from ammonia that is either present in air, human breath or ion-conducting membranes9, or generated from labile nitrogen-containing compounds (for example, nitrates, amines, nitrites and nitrogen oxides) that are typically present in the nitrogen gas stream10, in the atmosphere or even in the catalyst itself. Although these sources of experimental artefacts are beginning to be recognized and managed11,12, concerted efforts to develop effective electrochemical nitrogen reduction processes would benefit from benchmarking protocols for the reaction and from a standardized set of control experiments designed to identify and then eliminate or quantify the sources of contamination. Here we propose a rigorous procedure using 15N2 that enables us to reliably detect and quantify the electrochemical reduction of nitrogen to ammonia. We demonstrate experimentally the importance of various sources of contamination, and show how to remove labile nitrogen-containing compounds from the nitrogen gas as well as how to perform quantitative isotope measurements with cycling of 15N2 gas to reduce both contamination and the cost of isotope measurements. Following this protocol, we find that no ammonia is produced when using the most promising pure-metal catalysts for this reaction in aqueous media, and we successfully confirm and quantify ammonia synthesis using lithium electrodeposition in tetrahydrofuran13. The use of this rigorous protocol should help to prevent false positives from appearing in the literature, thus enabling the field to focus on viable pathways towards the practical electrochemical reduction of nitrogen to ammonia. A protocol for the electrochemical reduction of nitrogen to ammonia enables isotope-sensitive quantification of the ammonia produced and the identification and removal of contaminants.

819 citations

Journal ArticleDOI
TL;DR: This review briefly discusses the structure and preparation of the CHA structure-based zeolite catalysts, and summarizes the key learnings of the rather extensive (but not complete) characterisation work, and provides some mechanistic details emerging from these investigations.
Abstract: The ever increasing demand to develop highly fuel efficient engines coincides with the need to minimize air pollution originating from the exhaust gases of internal combustion engines. Dramatically improved fuel efficiency can be achieved at air-to-fuel ratios much higher than stoichiometric. In the presence of oxygen in large excess, however, traditional three-way catalysts are unable to reduce NOx. Among the number of lean-NOx reduction technologies, selective catalytic reduction (SCR) of NOx by NH3 over Cu- and Fe-ion exchanged zeolite catalysts has been extensively studied over the past 30+ years. Despite the significant advances in developing a viable practical zeolite-based catalyst for lean NOx reduction, the insufficient hydrothermal stabilities of the zeolite structures considered cast doubts about their real-world applicability. During the past decade renewed interest in zeolite-based lean NOx reduction was spurred by the discovery of the very high activity of Cu–SSZ-13 (and the isostructural Cu–SAPO-34) in the NH3-SCR of NOx. These new, small-pore zeolite-based catalysts not only exhibited very high NOx conversion and N2 selectivity, but also exhibited exceptionally high hydrothermal stability at high temperatures. In this review we summarize the key discoveries of the past ∼5 years that led to the introduction of these catalysts into practical applications. This review first briefly discusses the structure and preparation of the CHA structure-based zeolite catalysts, and then summarizes the key learnings of the rather extensive (but not complete) characterisation work. Then we summarize the key findings of reaction kinetic studies, and provide some mechanistic details emerging from these investigations. At the end of the review we highlight some of the issues that still need to be addressed in automotive exhaust control catalysis.

668 citations

Journal ArticleDOI
TL;DR: UV-Vis-NIR spectra of O2 activated samples reveal an intense and finely structured d-d quadruplet, unique to Cu-SSZ-13, which is persistent under SCR conditions.
Abstract: Cu-SSZ-13 has been characterized by different spectroscopic techniques and compared with Cu-ZSM-5 and Cu-β with similar Si/Al and Cu/Al ratios and prepared by the same ion exchange procedure. On vacuum activated samples, low temperature FTIR spectroscopy allowed us to appreciate a high concentration of reduced copper centres, i.e. isolated Cu+ ions located in different environments, able to form Cu+(N2), Cu+(CO)n (n = 1, 2, 3), and Cu+(NO)n (n = 1, 2) upon interaction with N2, CO and NO probe molecules, respectively. Low temperature FTIR, DRUV-Vis and EPR analysis on O2 activated samples revealed the presence of different Cu2+ species. New data and discussion are devoted to (i) [Cu–OH]+ species likely balanced by one framework Al atom; (ii) mono(μ-oxo)dicopper [Cu2(μ-O)]2+ dimers observed in Cu-ZSM-5 and Cu-β, but not in Cu-SSZ-13. UV-Vis-NIR spectra of O2 activated samples reveal an intense and finely structured d–d quadruplet, unique to Cu-SSZ-13, which is persistent under SCR conditions. This differs from the 22 700 cm−1 band of the mono(μ-oxo)dicopper species of the O2 activated Cu-ZSM-5, which disappears under SCR conditions. The EPR signal intensity sets Cu-β apart from the others.

305 citations

Journal ArticleDOI
TL;DR: In situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS), temperature-programmed desorption (TPD), and temperatureprogrammed surface reactions (TPSR) were employed to investigate the adsorption and reactive properties of Cu-SSZ-13 and Cu-SAPO-34 zeolite catalysts; these fully formulated washcoat cordierite monoliths were hydrothermally treated at 750°C in the simulated feed gases.
Abstract: In situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS), temperature-programmed desorption (TPD), and temperature-programmed surface reactions (TPSR) were employed to investigate the adsorption and reactive properties of Cu-SSZ-13 and Cu-SAPO-34 zeolite catalysts; these fully formulated washcoat cordierite monoliths were hydrothermally treated at 750 °C in the simulated feed gases. The intrinsic mechanism and reasons for the differences in NH3-SCR activity were proposed based on the characterization results. The in situ DRIFTS and TPD results showed that ammonia could adsorb on both the Lewis and Bronsted acidic sites on these two catalysts; the ammonia on the Bronsted acidic sites might be active in the NH3-SCR reaction. For the different NOx adsorption processes, the total NOx desorption levels followed the following sequence: NO

276 citations

Journal ArticleDOI
TL;DR: In this article, the development of Cu-chabazite (CHA) catalysts represents a significant technology breakthrough for the removal of NOx by selective catalytic reduction (SCR) with ammonia.
Abstract: The development of Cu-chabazite (CHA) catalysts, i.e. Cu-SSZ-13 and Cu-SAPO-34, represents a significant technology breakthrough for the removal of NOx by selective catalytic reduction (SCR) with ammonia. Cu-CHA catalysts show an excellent hydrothermal stability towards high temperature aging and wide active temperature windows for the ammonia SCR reaction. This work summarizes the recent progress in the development of the Cu-CHA catalysts for the NH3-SCR reaction. The state of Cu in the reaction and the preparation methods on the catalytic performance are discussed. The advances in the understanding of the reaction mechanism are reviewed. The hydrothermal stability of the typical Cu-CHA catalysts are compared.

263 citations

References
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Journal ArticleDOI
TL;DR: In this article, a nouvelle classe de tamis moleculaires, who peuvent etre utilises comme catalyseurs, supports de catalyseur, adsorbants ou echangeurs d'ions, correspondent a formule generale 0-0,3R•(Si x Al y P z )O 2 avec R=reste d'ammonium quaternaire ou une amine organique
Abstract: Donnees sur une nouvelle classe de tamis moleculaires, qui peuvent etre utilises comme catalyseurs, supports de catalyseurs, adsorbants ou echangeurs d'ions et qui correspondent a une formule generale 0-0,3R•(Si x Al y P z )O 2 avec R=reste d'ammonium quaternaire ou une amine organique

909 citations

Journal ArticleDOI
TL;DR: In this paper, the performance of a Cu ion-exchanged SSZ-13 zeolite in the selective catalytic reduction (SCR) of NO x with NH 3 was observed, in comparison with Cu-beta and ZSM-5 zeolites.

668 citations

Journal ArticleDOI
TL;DR: Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies is presented.
Abstract: Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies Pascal Granger* and Vasile I. Parvulescu* Unit e de Catalyse et de Chimie du Solide, UMR CNRS 8181, University of Lille 1, 59655 Villeneuve d’Ascq, France Department of Organic Chemistry, Biochemistry and Catalysis, University of Bucharest, Romania, 412 Regina Elisabeta Boulevard, Bucharest 030016, Romania

628 citations

Journal ArticleDOI
TL;DR: The NH3-SCR activity of small-pore zeolites, such as Cu-SSZ-13 and Cu-SAPO-34, was investigated using a high-throughput reactor system in this article.
Abstract: The NH3-SCR activity of the small-pore zeolites, Cu-SSZ-13, Cu-SSZ-16, and Cu-SAPO-34, is investigated using a high-throughput reactor system. These copper exchanged small-pore zeolites have high SCR activity between 150 and 500 °C and are shown to be much more hydrothermally stable than the medium-pore zeolite, Cu-ZSM-5. The degree of copper exchange, the dimensionality of the framework, and heteroatom framework substitution all impact the SCR activity and hydrothermal stability of the materials. Of the small-pore zeolites tested, Cu-SSZ-13 and Cu-SAPO-34 display superior SCR performance, both before and after high-temperature hydrothermal treatment.

596 citations

Journal ArticleDOI
TL;DR: In this article, the effects of hydrothermal treatment on model Cu/zeolite catalysts were investigated to better understand the nature of Cu species for the selective catalytic reduction of NO{sub x} by NH{sub 3}.

428 citations