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- Auvray, Xavier, 1986, et al.
(författare)
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Local ammonia storage and ammonia inhibition in a monolithic copper-beta zeolite SCR catalyst
- 2012
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 126, s. 144-152
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Tidskriftsartikel (refereegranskat)abstract
- Selective catalytic reduction of NO with NH3 was studied on a Cu-beta zeolite catalyst, with specific focus on the distributed NH3 capacity utilization and inhibition. In addition, several other relevant catalyst parameter distributions were quantified including the SCR zone, or catalyst region where SCR occurs, and NO and NH3 oxidation. We show that the full NH3 capacity (100% coverage) is used within the SCR zone for a range of temperatures. By corollary, unused NH3 capacity exists downstream of the SCR zone. Consequently, the unused capacity relative to the total capacity is indicative of the portion of the catalyst unused for SCR. Dynamic NH3 inhibition distributions, which create local transient conversion inflections, are measured. Dynamic inhibition is observed where the gas phase NH3 and NO concentrations are high, driving rapid NH3 coverage buildup and SCR. Accordingly, we observe dynamic inhibition at low temperatures and in hydrothermally aged states, but predict its existence very near the catalyst front in higher conversion conditions where we did not specifically monitor its impact. While this paper addresses some general distributed SCR performance parameters including Oxidation and SCR zone, our major new contributions are associated with the NH3 capacity saturation within the SCR zone and dynamic inhibition distributions and the associated observations. These new insights are relevant to developing accurate models, designs and control strategies for automotive SCR catalyst applications.
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- O Reese, Matthew, et al.
(författare)
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Consensus stability testing protocols for organic photovoltaic materials and devices
- 2011
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Ingår i: SOLAR ENERGY MATERIALS AND SOLAR CELLS. - : Elsevier Science B.V., Amsterdam.. - 0927-0248. ; 95:5, s. 1253-1267
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Tidskriftsartikel (refereegranskat)abstract
- Procedures for testing organic solar cell devices and modules with respect to stability and operational lifetime are described. The descriptions represent a consensus of the discussion and conclusions reached during the first 3 years of the international summit on OPV stability (ISOS). The procedures include directions for shelf life testing, outdoor testing, laboratory weathering testing and thermal cycling testing, as well as guidelines for reporting data. These procedures are not meant to be qualification tests, but rather generally agreed test conditions and practices to allow ready comparison between laboratories and to help improving the reliability of reported values. Failure mechanisms and detailed degradation mechanisms are not covered in this report.
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- Currier, Russell W, et al.
(författare)
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The evolution of infectious agents in relation to sex in animals and humans: brief discussions of some individual organisms.
- 2011
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Ingår i: Annals of the New York Academy of Sciences. - : Wiley. - 1749-6632 .- 0077-8923. ; 1230, s. 74-107, s. 74-107
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Forskningsöversikt (refereegranskat)abstract
- The following series of concise summaries addresses the evolution of infectious agents in relation to sex in animals and humans from the perspective of three specific questions: (1) what have we learned about the likely origin and phylogeny, up to the establishment of the infectious agent in the genital econiche, including the relative frequency of its sexual transmission; (2) what further research is needed to provide additional knowledge on some of these evolutionary aspects; and (3) what evolutionary considerations might aid in providing novel approaches to the more practical clinical and public health issues facing us currently and in the future?
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- Li, J. H., et al.
(författare)
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Characterization of Active Species in Cu-Beta Zeolite by Temperature-Programmed Reduction Mass Spectrometry (TPR-MS)
- 2013
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 201-204
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Tidskriftsartikel (refereegranskat)abstract
- The number and type of copper species present in an under-exchanged Cu-Beta zeolite catalyst were characterized using temperature-programmed reduction mass spectrometry (TPR-MS). Both H-2 consumption and H2O evolution were tracked, yielding additional insights into the nature of Cu species. Prior to the TPR-MS tests, catalyst samples were subjected to various high- temperature aging treatments in the presence of O-2 in He, in order to assist with interrogating and resolving different types of sites. Absence of reducible species in the precursor material was confirmed by subjecting the H-form of the same zeolite to the TPR. Upon aging at temperatures below 700 A degrees C, the TPR pattern showed several distinct peaks of different intensities. Aging at 800 A degrees C led to shifting and broadening of these H-2 consumption peaks, as well as to some reduction of the integral amount of the reducible sites. The 900 A degrees C exposure resulted in a drastic change of the TPR pattern, with several new well-resolved H-2 consumption peaks, indicative of drastic changes in the catalyst structure. The integral amount of H-2 consumed quantitatively matched the amount of Cu species present in the catalyst, assuming the stoichiometry. The combination of experimental findings in this work lends support to a hypothesis that different TPR peaks are indicative of different types of sites rather than of step-wise reduction of copper species.
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- Mihai, Oana, 1975, et al.
(författare)
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The effect of Cu-loading on different reactions involved in NH3-SCR over Cu-BEA catalysts
- 2014
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 311, s. 170-181
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the effect of varying copper loading in Cu-BEA on different reactions involved in the SCR mechanism. The catalysts were characterized by BET, ICP-AES, and UV-Vis. Enlarged ammonia storage was observed when increasing the copper loading mainly owing to loosely bonded NH3, but for over-exchanged samples, a new high-temperature shoulder was also observed. The N2O production significantly grew with increasing copper loading. In addition, the reaction rates of NO oxidation and NH3 oxidation per Cu site were higher on the high-loaded copper samples compared to those with lower loading. However, the opposite results were found for NH3 SCR, but differences were small for this reaction. Ammonium nitrate formation and decomposition were examined during a variety of temperature-programmed desorption (TPD) experiments, and three regions related to the presence of acid sites and low- versus high-loaded copper sites were observed. When dosing NO2 before NH3, ammonium nitrate species were formed but in lower amounts than if NH3 and NO2 were dosed simultaneously.
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- Wilken, Norman, 1983, et al.
(författare)
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Heat of adsorption for NH3, NO2 and NO on Cu-Beta zeolite using microcalorimeter for NH3 SCR applications
- 2010
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 151:3-4, s. 237-243
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Tidskriftsartikel (refereegranskat)abstract
- Microcalorimetry is a powerful technique with which to measure the heat of adsorption (Delta H), producing values that are very important when developing kinetic models. The method provides a way of determining these parameters independently. For kinetic models describing NH3 SCR it is critical to be able to accurately describe the storage of ammonia and NO in order to simulate rapid transients occurring in the experiments. The objective of our study is to measure the heat of adsorption of NH3, NO2 and NO on Cu-Beta. An ammonia TPD experiment was conducted at 150 degrees C using the microcalorimeter, resulting in the observation of an exotherm when introducing ammonia due to adsorption. This resulted in an average heat of adsorption of -100 kJ/mol. A good reproducibility was found when using a second sample, resulting in -97 kJ/mol. In order to investigate the coverage dependence of the heat of adsorption, an ammonia stepwise experiment was conducted. First, the catalyst was exposed to NH3 at 500 degrees C, resulting in the adsorption of strongly bound ammonia and obtaining a heat of adsorption of -110 kJ/mol. Thereafter, the catalyst was cooled in Ar and at 400 degrees C, NH3 was again introduced. Due to that the temperature is lower the ammonia that adsorbed was weaker. The procedure was repeated at 300, 200 and 100 degrees C, resulting in a coverage dependent activation energy for ammonia desorption (if assuming zero activation for adsorption) according to the following formula: E-desorption,NH3 = 120.0 (1 - 0.38 theta(NH3)) where theta(NH3) is the coverage of ammonia on the surface. The NO and NO2 adsorption and desorption were investigated using NO and NO2 TPD experiments, respectively. For the NO2 TPD experiment, approximately three NO2 were stored for each NO produced, corresponding to the disproportionation mechanism. This resulted in Delta H of -65 kJ/mol per NO2 consumed. The NO TPD experiment resulted in that only small amounts of NO was adsorbed. (C) 2010 Elsevier B.V. All rights reserved.
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