Author
Manfred Koebel
Bio: Manfred Koebel is an academic researcher from Paul Scherrer Institute. The author has contributed to research in topics: Selective catalytic reduction & Catalysis. The author has an hindex of 19, co-authored 25 publications receiving 3341 citations.
Topics: Selective catalytic reduction, Catalysis, NOx, Isocyanic acid, Ammonia
Papers
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TL;DR: In this article, the authors discuss the fundamental problems and challenges if urea-SCR is extended to mobile applications, including the control strategy for urea dosing, the high freezing point of urea, and the long term stability of the catalyst.
1,026 citations
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TL;DR: The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases containing both NO and NO2 was investigated in this article, where the two main reactions are 4NH3 + 2NO + 2 NO2 → 4N2 + 6H2O and 2NH3+ 2NO2 → NH4NO3 + N2 + H2O.
Abstract: The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases containing both NO and NO2 was investigated. The two main reactions are 4NH3 + 2NO + 2NO2 → 4N2 + 6H2O and 2NH3 + 2NO2 → NH4NO3 + N2 + H2O. The “fast SCR reaction” exhibits a reaction rate at least 10 times higher than that of the well-known standard SCR reaction with pure NO and dominates at temperatures above 200 °C. At lower temperatures, the “ammonium nitrate route” becomes increasingly important. Under extreme conditions, e.g., a powder catalyst at T ≈ 140 °C, the ammonium nitrate route may be responsible for the whole NOx conversion observed. This reaction leads to the formation of ammonium nitrate within the pores of the catalyst and a temporary deactivation. For a typical monolithic sample, the lower threshold temperature at which no degradation of catalyst activity with time is observed is around 180 °C. The ammonium nitrate route is interesting from a standpoint of general DeNOx mechanisms: This reac...
393 citations
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TL;DR: In this paper, the authors investigated the effect of ammonium nitrate on the SCR reaction in the presence of NO and showed that ammonium Nitrate can lead to the formation of NO 2.
369 citations
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TL;DR: In this article, the catalytic oxidation of NO was studied on a catalyst consisting of platinum supported on SiO2 and the kinetic behavior over Pt/SiO2 with a platinum loading of 2.5% was investigated in a feed containing 5% water and various concentrations of oxygen, nitrogen monoxide and nitrogen dioxide.
Abstract: The catalytic oxidation of NO was studied on a catalyst consisting of platinum supported on SiO2. The kinetic behavior over Pt/SiO2 with a platinum loading of 2.5 wt.% was investigated in a feed containing 5% water and various concentrations of oxygen, nitrogen monoxide and nitrogen dioxide. The conversion of NO to NO2 increases when the oxygen concentration is increased from 0.1 to 10%, but levels off at higher concentrations. Increasing feed concentrations of NO lead to a decrease in the conversion to NO2. The formation of NO2 is also depressed by the addition of NO2 to the feed. Both observations suggest that the oxidation of NO on Pt/SiO2 is autoinhibited by the reaction product NO2. Further experiments have shown that the inhibition caused by NO2 is mostly persistent, i.e. a deactivation of the catalyst occurs. A pretreatment at 250 °C in a feed containing 500 ppm NO2 causes a very strong decrease in activity. However, the initial activity can be restored either by a thermal regeneration at 650 °C in air or by a regeneration under reducing conditions at 250 °C, e.g. in a feed containing NH3. This suggests that the deactivation by NO2 is due to the formation of a thin layer of platinum oxide covering the platinum surface at least partially.
214 citations
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TL;DR: In this paper, an energy analysis of the thermal decomposition of solid urea and urea solutions is presented, and the results are discussed in view of urea selective catalytic reduction (SCR) for automotive DeNOx systems.
Abstract: An energetic analysis of the thermal decomposition of solid urea and urea solutions is presented, and the results are discussed in view of urea selective catalytic reduction (SCR) for automotive DeNOx systems. Various types of decomposition reactors are possible which differ in their effectiveness to produce ammonia from urea. For reasons of simplicity, the decomposition is usually performed by atomizing urea solutions directly into the hot exhaust. However, this technique suffers from short residence times, leading to incomplete decomposition into ammonia and isocyanic acid and causing a significant performance loss of the SCR catalyst. The thermal decomposition out of the main exhaust stream allows much increased residence times for the process of urea decomposition. A reactor utilizing a partial stream of the exhaust seems particularly promising, especially if such a reactor includes a hydrolyzing catalyst, leading to ammonia practically free from isocyanic acid.
193 citations
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TL;DR: In this paper, photo-induced superhydrophilicity was used on the surface of a wide-band gap semiconductor like titanium dioxide (TiO 2 ) for photocatalytic activity towards environmentally hazardous compounds.
4,241 citations
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National Institute of Advanced Industrial Science and Technology1, University of Bari2, Air Products & Chemicals3, University of Delaware4, University of Pittsburgh5, University of California, Berkeley6, California Institute of Technology7, Brookhaven National Laboratory8, Karlsruhe Institute of Technology9, Environmental Molecular Sciences Laboratory10, Tokyo Institute of Technology11, National Renewable Energy Laboratory12, Los Alamos National Laboratory13, University of Louisville14, Texas A&M University15, Sandia National Laboratories16, Northwestern University17, DuPont18, Emory University19, University of Oklahoma20, University of Southern California21, University of Minnesota22, Pennsylvania State University23, Idaho National Laboratory24
TL;DR: The goal of the "Opportunities for Catalysis Research in Carbon Management" workshop was to review within the context of greenhouse gas/carbon issues the current state of knowledge, barriers to further scientific and technological progress, and basic scientific research needs in the areas of H2 generation and utilization.
Abstract: There is increased recognition by the world’s scientific, industrial, and political communities that the concentrations of greenhouse gases in the earth’s
atmosphere, particularly CO_2, are increasing. For
example, recent studies of Antarctic ice cores to
depths of over 3600 m, spanning over 420 000 years,
indicate an 80 ppm increase in atmospheric CO_2 in
the past 200 years (with most of this increase
occurring in the past 50 years) compared to the
previous 80 ppm increase that required 10 000 years.2
The 160 nation Framework Convention for Climate
Change (FCCC) in Kyoto focused world attention on
possible links between CO2 and future climate change
and active discussion of these issues continues.3 In
the United States, the PCAST report4 “Federal
Energy Research and Development for the Challenges
of the Twenty First Century” focused attention
on the growing worldwide demand for energy and the
need to move away from current fossil fuel utilization.
According to the U.S. DOE Energy Information
Administration,5 carbon emission from the transportation
(air, ground, sea), industrial (heavy manufacturing,
agriculture, construction, mining, chemicals,
petroleum), buildings (internal heating, cooling, lighting),
and electrical (power generation) sectors of the
World economy amounted to ca. 1823 million metric
tons (MMT) in 1990, with an estimated increase to
2466 MMT in 2008-2012 (Table 1).
1,220 citations
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TL;DR: In this article, the authors discuss the fundamental problems and challenges if urea-SCR is extended to mobile applications, including the control strategy for urea dosing, the high freezing point of urea, and the long term stability of the catalyst.
1,026 citations
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TL;DR: In this paper, a series of manganese-cerium oxide catalysts were prepared by co-precipitation method and used for low temperature selective catalytic reduction of NO x with ammonia in the presence of excess O 2.
Abstract: A series of manganese-cerium oxide catalysts were prepared by co-precipitation method and used for low temperature selective catalytic reduction (SCR) of NO x with ammonia in the presence of excess O 2 . These catalysts were characterized by X-ray diffraction (XRD), surface area measurement and FTIR. The experimental results showed that the best Mn-Ce mixed-oxide catalyst yielded 95% NO conversion at 150 °C at a space velocity of 42,000 h −1 . As the manganese content was increased from 0 to 40% (i.e. the molar ratio of Mn/(Mn+Ce)), NO conversion increased significantly, but decreased at higher manganese contents. The most active catalyst was obtained with a molar Mn/(Mn+Ce) ratio of 0.4. Only N 2 rather than N 2 O was found in the product when the temperature was below 150 °C. At higher temperatures, trace amounts of N 2 O were detected. A mechanistic pathway for this reaction was proposed based on earlier findings and FTIR results obtained in this work. The initial step was the adsorption of NH 3 on Lewis acid sites of catalyst, followed by reaction with nitrite species to produce N 2 and H 2 O. Possible intermediates are proposed and all the intermediates could transform into NH 2 NO, which could further react to produce N 2 and H 2 O.
960 citations
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TL;DR: In this article, the authors describe the work carried out in characterizing, developing, and understanding this catalyst technology for application in mobile exhaust gas aftertreatment, which includes five general steps involved in NOx reduction to N2 on NSR catalysts; NO oxidation, NO2 and NO sorption leading to nitrite and nitrate species.
Abstract: Over the last several years, nitrogen oxide(s) (NOx) storage/reduction (NSR) catalysts, also referred to as NOx adsorbers or lean NOx traps, have been developed as an aftertreatment technology to reduce NOx emissions from lean‐burn power sources. NSR operation is cyclic: during the lean part of the cycle, NOx are trapped on the catalyst; intermittent rich excursions are used to reduce the NOx to N2 and restore the original catalyst surface; and lean operation then resumes. This review will describe the work carried out in characterizing, developing, and understanding this catalyst technology for application in mobile exhaust‐gas aftertreatment. The discussion will first encompass the reaction process fundamentals, which include five general steps involved in NOx reduction to N2 on NSR catalysts; NO oxidation, NO2 and NO sorption leading to nitrite and nitrate species, reductant evolution, NOx release, and finally NOx reduction to N2. Major unresolved issues and questions are listed at the end of ...
846 citations