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Walter S, Schwanzer P, Hagen G, Rabl HP, Dietrich M, Moos R. Soot Monitoring of Gasoline Particulate Filters Using a Radio-Frequency-Based Sensor. SENSORS (BASEL, SWITZERLAND) 2023; 23:7861. [PMID: 37765917 PMCID: PMC10536291 DOI: 10.3390/s23187861] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Revised: 08/11/2023] [Accepted: 08/14/2023] [Indexed: 09/29/2023]
Abstract
Owing to increasingly stringent emission limits, particulate filters have become mandatory for gasoline-engine vehicles. Monitoring their soot loading is necessary for error-free operation. The state-of-the-art differential pressure sensors suffer from inaccuracies due to small amounts of stored soot combined with exhaust gas conditions that lead to partial regeneration. As an alternative approach, radio-frequency-based (RF) sensors can accurately measure the soot loading, even under these conditions, by detecting soot through its dielectric properties. However, they face a different challenge as their sensitivity may depend on the engine operation conditions during soot formation. In this article, this influence is evaluated in more detail. Various soot samples were generated on an engine test bench. Their dielectric properties were measured using the microwave cavity perturbation (MCP) method and compared with the corresponding sensitivity of the RF sensor determined on a lab test bench. Both showed similar behavior. The values for the soot samples themselves, however, differed significantly from each other. A way to correct for this cross-sensitivity was found in the influence of exhaust gas humidity on the RF sensor, which can be correlated with the engine load. By evaluating this influence during significant humidity changes, such as fuel cuts, it could be used to correct the influence of the engineon the RF sensor.
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Affiliation(s)
- Stefanie Walter
- Bayreuth Engine Research Center (BERC), Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany
| | - Peter Schwanzer
- Combustion Engines and Emissions Control Laboratory, Ostbayerische Technische Hochschule Regensburg, 93053 Regensburg, Germany
| | - Gunter Hagen
- Bayreuth Engine Research Center (BERC), Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany
| | - Hans-Peter Rabl
- Combustion Engines and Emissions Control Laboratory, Ostbayerische Technische Hochschule Regensburg, 93053 Regensburg, Germany
| | | | - Ralf Moos
- Bayreuth Engine Research Center (BERC), Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany
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2
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Abstract
Dynamic motion of NH3-solvated Cu sites in Cu-chabazite (Cu-CHA) zeolites, which are the most promising and state-of-the-art catalysts for ammonia-assisted selective reduction of NOx (NH3-SCR) in the aftertreatment of diesel exhausts, represents a unique phenomenon linking heterogeneous and homogeneous catalysis. This review first summarizes recent advances in the theoretical understanding of such low-temperature Cu dynamics. Specifically, evidence of both intra-cage and inter-cage Cu motions, given by ab initio molecular dynamics (AIMD) or metadynamics simulations, will be highlighted. Then, we will show how, among others, synchrotron-based X-ray spectroscopy, vibrational and optical spectroscopy (diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) and diffuse reflection ultraviolet-visible spectroscopy (DRUVS)), electron paramagnetic spectroscopy (EPR), and impedance spectroscopy (IS) can be combined and complement each other to follow the evolution of coordinative environment and the local structure of Cu centers during low-temperature NH3-SCR reactions. Furthermore, the essential role of Cu dynamics in the tuning of low-temperature Cu redox, in the preparation of highly dispersed Cu-CHA catalysts by solid-state ion exchange method, and in the direct monitoring of NH3 storage and conversion will be presented. Based on the achieved mechanistic insights, we will discuss briefly the new perspectives in manipulating Cu dynamics to improve low-temperature NH3-SCR efficiency as well as in the understanding of other important reactions, such as selective methane-to-methanol oxidation and ethene dimerization, catalyzed by metal ion-exchanged zeolites.
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Chen P, Rizzotto V, Khetan A, Xie K, Moos R, Pitsch H, Ye D, Simon U. Mechanistic Understanding of Cu-CHA Catalyst as Sensor for Direct NH 3-SCR Monitoring: The Role of Cu Mobility. ACS APPLIED MATERIALS & INTERFACES 2019; 11:8097-8105. [PMID: 30706712 DOI: 10.1021/acsami.8b22104] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The concept to utilize a catalyst directly as a sensor is fundamentally and technically attractive for a number of catalytic applications, in particular, for the catalytic abatement of automotive emission. Here, we explore the potential of microporous copper-exchanged chabazite (Cu-CHA, including Cu-SSZ-13 and Cu-SAPO-34) zeolite catalysts, which are used commercially in the selective catalytic reduction of automotive nitrogen oxide emission by NH3 (NH3-SCR), as impedance sensor elements to monitor directly the NH3-SCR process. The NH3-SCR sensing behavior of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts at typical reaction temperatures (i.e., 200 and 350 °C) was evaluated according to the change of ionic conductivity and was mechanistically investigated by complex impedance-based in situ modulus spectroscopy. Short-range (local) movement of Cu ions within the zeolite structure was found to determine largely the NH3-SCR sensing behavior of both catalysts. Formation of NH3-solvated, highly mobile CuI species showed a predominant influence on the ionic conductivity of both catalysts and, consequently, hindered NH3-SCR sensing at 200 °C. Density functional theory calculations over a model Cu-SAPO-34 system revealed that CuII reduction to CuI by coadsorbed NH3 and NO weakened significantly the coordination of the Cu site to the CHA framework, enabling high mobility of CuI species that influences substantially the NH3-SCR sensing. The in situ spectroscopic and theoretical investigations not only unveil the mechanisms of Cu-CHA catalyst as sensor elements for direct NH3-SCR monitoring but also allow us to get insights into the speciation of active Cu sites in NH3-SCR under different reaction conditions with varied temperatures and gas compositions.
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Affiliation(s)
- Peirong Chen
- Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy , South China University of Technology , Guangzhou 510006 , China
- Institute of Inorganic Chemistry , RWTH Aachen University , Landoltweg 1 , Aachen 52074 , Germany
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
| | - Valentina Rizzotto
- Institute of Inorganic Chemistry , RWTH Aachen University , Landoltweg 1 , Aachen 52074 , Germany
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
| | - Abhishek Khetan
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
- Institute for Combustion Technology , RWTH Aachen University , Templergraben 64 , Aachen 52056 , Germany
- Department of Mechanical Engineering , Carnegie Mellon University , 5000 Forbes Avenue , Pittsburgh , Pennsylvania 15213 , United States
| | - Kunpeng Xie
- Institute of Inorganic Chemistry , RWTH Aachen University , Landoltweg 1 , Aachen 52074 , Germany
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
| | - Ralf Moos
- Department of Functional Materials and Bayreuth Engine Research Center (BERC) , University of Bayreuth , Bayreuth 95440 , Germany
| | - Heinz Pitsch
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
- Institute for Combustion Technology , RWTH Aachen University , Templergraben 64 , Aachen 52056 , Germany
| | - Daiqi Ye
- Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy , South China University of Technology , Guangzhou 510006 , China
| | - Ulrich Simon
- Institute of Inorganic Chemistry , RWTH Aachen University , Landoltweg 1 , Aachen 52074 , Germany
- Center for Automotive Catalytic Systems Aachen , RWTH Aachen University , Aachen 52062 , Germany
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4
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Modelling Both the NH3 Storage on Automotive SCR Catalysts and the Radio-Frequency-Based Response. Top Catal 2019. [DOI: 10.1007/s11244-019-01140-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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5
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Chen P, Rizzotto V, Xie K, Simon U. Tracking mobile active sites and intermediates in NH3-SCR over zeolite catalysts by impedance-based in situ spectroscopy. REACT CHEM ENG 2019. [DOI: 10.1039/c8re00283e] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Impedance-based in situ spectroscopy allows direct tracking of the mobile active sites and reaction intermediates in NH3-SCR over zeolite catalysts.
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Affiliation(s)
- Peirong Chen
- Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control
- School of Environment and Energy
- South China University of Technology
- 510006 Guangzhou
- China
| | - Valentina Rizzotto
- Institute of Inorganic Chemistry
- RWTH Aachen University
- 52074 Aachen
- Germany
- Center for Automotive Catalytic Systems Aachen
| | - Kunpeng Xie
- Institute of Inorganic Chemistry
- RWTH Aachen University
- 52074 Aachen
- Germany
- Center for Automotive Catalytic Systems Aachen
| | - Ulrich Simon
- Institute of Inorganic Chemistry
- RWTH Aachen University
- 52074 Aachen
- Germany
- Center for Automotive Catalytic Systems Aachen
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6
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Storage and Oxidation of Oxygen-Free and Oxygenated Hydrocarbons on a Pt–Pd Series Production Oxidation Catalyst. Top Catal 2018. [DOI: 10.1007/s11244-018-1109-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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7
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Mobility of NH3-Solvated CuII Ions in Cu-SSZ-13 and Cu-ZSM-5 NH3-SCR Catalysts: A Comparative Impedance Spectroscopy Study. Catalysts 2018. [DOI: 10.3390/catal8040162] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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8
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Radio-Frequency-Controlled Urea Dosing for NH₃-SCR Catalysts: NH₃ Storage Influence to Catalyst Performance under Transient Conditions. SENSORS 2017; 17:s17122746. [PMID: 29182589 PMCID: PMC5751734 DOI: 10.3390/s17122746] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Accepted: 11/23/2017] [Indexed: 11/16/2022]
Abstract
Current developments in exhaust gas aftertreatment led to a huge mistrust in diesel driven passenger cars due to their NOx emissions being too high. The selective catalytic reduction (SCR) with ammonia (NH₃) as reducing agent is the only approach today with the capability to meet upcoming emission limits. Therefore, the radio-frequency-based (RF) catalyst state determination to monitor the NH₃ loading on SCR catalysts has a huge potential in emission reduction. Recent work on this topic proved the basic capability of this technique under realistic conditions on an engine test bench. In these studies, an RF system calibration for the serial type SCR catalyst Cu-SSZ-13 was developed and different approaches for a temperature dependent NH₃ storage were determined. This paper continues this work and uses a fully calibrated RF-SCR system under transient conditions to compare different directly measured and controlled NH₃ storage levels, and NH₃ target curves. It could be clearly demonstrated that the right NH₃ target curve, together with a direct control on the desired level by the RF system, is able to operate the SCR system with the maximum possible NOx conversion efficiency and without NH₃ slip.
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9
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Bogner A, Steiner C, Walter S, Kita J, Hagen G, Moos R. Planar Microstrip Ring Resonators for Microwave-Based Gas Sensing: Design Aspects and Initial Transducers for Humidity and Ammonia Sensing. SENSORS (BASEL, SWITZERLAND) 2017; 17:E2422. [PMID: 29064438 PMCID: PMC5677052 DOI: 10.3390/s17102422] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Revised: 10/16/2017] [Accepted: 10/17/2017] [Indexed: 12/02/2022]
Abstract
A planar microstrip ring resonator structure on alumina was developed using the commercial FEM software COMSOL. Design parameters were evaluated, eventually leading to an optimized design of a miniaturized microwave gas sensor. The sensor was covered with a zeolite film. The device was successfully operated at around 8.5 GHz at room temperature as a humidity sensor. In the next step, an additional planar heater will be included on the reverse side of the resonator structure to allow for testing of gas-sensitive materials under sensor conditions.
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Affiliation(s)
- Andreas Bogner
- Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany.
| | - Carsten Steiner
- Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany.
| | - Stefanie Walter
- Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany.
| | - Jaroslaw Kita
- Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany.
| | - Gunter Hagen
- Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany.
| | - Ralf Moos
- Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany.
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10
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Radio-Frequency-Based NH₃-Selective Catalytic Reduction Catalyst Control: Studies on Temperature Dependency and Humidity Influences. SENSORS 2017; 17:s17071615. [PMID: 28704929 PMCID: PMC5539605 DOI: 10.3390/s17071615] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/21/2017] [Revised: 06/23/2017] [Accepted: 06/28/2017] [Indexed: 11/24/2022]
Abstract
The upcoming more stringent automotive emission legislations and current developments have promoted new technologies for more precise and reliable catalyst control. For this purpose, radio-frequency-based (RF) catalyst state determination offers the only approach for directly measuring the NH3 loading on selective catalytic reduction (SCR) catalysts and the state of other catalysts and filter systems. Recently, the ability of this technique to directly control the urea dosing on a current NH3 storing zeolite catalyst has been demonstrated on an engine dynamometer for the first time and this paper continues that work. Therefore, a well-known serial-type and zeolite-based SCR catalyst (Cu-SSZ-13) was investigated under deliberately chosen high space velocities. At first, the full functionality of the RF system with Cu-SSZ-13 as sample was tested successfully. By direct RF-based NH3 storage control, the influence of the storage degree on the catalyst performance, i.e., on NOx conversion and NH3 slip, was investigated in a temperature range between 250 and 400 °C. For each operation point, an ideal and a critical NH3 storage degree was found and analyzed in the whole temperature range. Based on the data of all experimental runs, temperature dependent calibration functions were developed as a basis for upcoming tests under transient conditions. Additionally, the influence of exhaust humidity was observed with special focus on cold start water and its effects to the RF signals.
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12
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Chen P, Jabłońska M, Weide P, Caumanns T, Weirich T, Muhler M, Moos R, Palkovits R, Simon U. Formation and Effect of NH4+ Intermediates in NH3–SCR over Fe-ZSM-5 Zeolite Catalysts. ACS Catal 2016. [DOI: 10.1021/acscatal.6b02496] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Peirong Chen
- Institute
of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
| | - Magdalena Jabłońska
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
- Chair
of Heterogeneous Catalysis and Chemical Technology, RWTH Aachen University, Worringerweg 2, 52074 Aachen, Germany
| | - Philipp Weide
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Tobias Caumanns
- Central
Facility for Electron Microscopy, RWTH Aachen University, 52074 Aachen, Germany
| | - Thomas Weirich
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
- Central
Facility for Electron Microscopy, RWTH Aachen University, 52074 Aachen, Germany
| | - Martin Muhler
- Laboratory
of Industrial Chemistry, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Ralf Moos
- Department
of Functional Materials, Bayreuth Engine Research Center and Zentrum
für Energietechnik, University of Bayreuth, Universitätsstraße
30, 95440 Bayreuth, Germany
| | - Regina Palkovits
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
- Chair
of Heterogeneous Catalysis and Chemical Technology, RWTH Aachen University, Worringerweg 2, 52074 Aachen, Germany
| | - Ulrich Simon
- Institute
of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
- Center
for Automotive Catalytic Systems Aachen, RWTH Aachen University, Aachen, Germany
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13
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Chen P, Rauch D, Weide P, Schönebaum S, Simons T, Muhler M, Moos R, Simon U. The effect of Cu and Fe cations on NH3-supported proton transport in DeNOx-SCR zeolite catalysts. Catal Sci Technol 2016. [DOI: 10.1039/c6cy00452k] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Proton transport studies revealed the different influence of Fe and Cu cations on the NH3–zeolite interaction and the NO–zeolite interaction in the presence of adsorbed NH3.
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Affiliation(s)
- Peirong Chen
- Institute of Inorganic Chemistry (IAC)
- RWTH Aachen University
- 52074 Aachen
- Germany
- Center for Automotive Catalytic Systems Aachen (ACA)
| | - Dieter Rauch
- Department of Functional Materials
- Bayreuth Engine Research Center (BERC)
- University of Bayreuth
- 95440 Bayreuth
- Germany
| | - Philipp Weide
- Laboratory of Industrial Chemistry
- Ruhr-University Bochum
- 44801 Bochum
- Germany
| | - Simon Schönebaum
- Institute of Inorganic Chemistry (IAC)
- RWTH Aachen University
- 52074 Aachen
- Germany
- Center for Automotive Catalytic Systems Aachen (ACA)
| | - Thomas Simons
- Institute of Inorganic Chemistry (IAC)
- RWTH Aachen University
- 52074 Aachen
- Germany
- Center for Automotive Catalytic Systems Aachen (ACA)
| | - Martin Muhler
- Laboratory of Industrial Chemistry
- Ruhr-University Bochum
- 44801 Bochum
- Germany
| | - Ralf Moos
- Department of Functional Materials
- Bayreuth Engine Research Center (BERC)
- University of Bayreuth
- 95440 Bayreuth
- Germany
| | - Ulrich Simon
- Institute of Inorganic Chemistry (IAC)
- RWTH Aachen University
- 52074 Aachen
- Germany
- Center for Automotive Catalytic Systems Aachen (ACA)
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