86,521 research outputs found
Catalyst systems for selective catalytic reduction + NO: X trapping: From fundamental understanding of the standard SCR reaction to practical applications for lean exhaust after-treatment
No full textWe have developed chemical trapping techniques as a novel tool to assess the nature of unstable reaction intermediates in the standard SCR reaction at low temperatures (120-200 °C). For this purpose, we have conducted transient response experiments over mechanical mixtures of an SCR catalyst (Fe-ZSM-5 or Cu-CHA) and a NOx storage material (BaO/Al2O3), which is able to trap and stabilize highly reactive NOx species. The results conclusively confirm that NO oxidative activation forms a gaseous intermediate, which acts like a nitrite precursor (e.g. HONO/N2O3) and is eventually stored on BaO/Al2O3. Such a species is also able to react with ammonia to produce N2, and is therefore proposed as a key intermediate of the standard SCR mechanism. We have further demonstrated that the capability of chemical trapping mechanical mixtures to capture NO in O2 at low temperature can also be exploited in practical applications for NOx emission control during cold start transients of diesel vehicles. In fact, such systems (SCR catalyst + NOx storage material) are characterized by an intrinsic dual functionality, being able both to store NOx when urea cannot be injected (e.g. below 170 °C) and to reduce the stored NOx with ammonia at higher temperatures in a single device. Accordingly, these mixtures have been renamed adsorption + selective catalytic reduction (AdSCR) systems. This review will summarize the main results achieved when implementing mechanical mixtures of NOx adsorbers and SCR catalysts both for fundamental understanding of the standard SCR mechanism and for abatement of cold start emissions
AdSCR Systems (Adsorption + Selective Catalytic Reduction): Analysis of the Influence of H2O and CO2 on Low Temperature NOx Emission Reduction Performances
No full textThe removal of NOx from low-temperature diesel engine emissions still represents a big challenge in view of the upcoming more stringent worldwide regulations. In our previous studies, we proved the ability of novel AdSCR (Adsorption + Selective Catalytic Reduction) systems, based on the combination of a chemical trapping compound and a conventional SCR catalyst, to trap cold start NOx emissions and to desorb and simultaneously reduce them with ammonia at higher temperature. In the present work, we extend the investigation of Cu-CHA + BaO/Al2O3 systems under more realistic conditions, focusing on the impact of H2O and CO2. The experimental results reveal a reduction of the AdSCR system performances with respect to dry and CO2-free conditions. Despite this, the system is still able to store and reduce NOx. The NOx storage capacity on barium oxide is more affected by the presence of CO2 than by H2O. However, H2O hinders the NO oxidative activation in the zeolite cages, which is a fundamental step in order to be able to trap NOx on the storage material at low temperature. We further demonstrate that the detrimental effect of H2O can be mitigated by small amounts of NO2 in the gaseous feed or by including a 13X zeolite guard bed prior to the AdSCR bed
Review of hydrocarbon poisoning and deactivation effects on Cu- Zeolite, fe-zeolite, and vanadium-based selective catalytic reduction catalysts for nox removal from lean exhausts
No full textLow-temperature operation of NH3-SCR (selective catalytic reduction) systems for NOx abatement in lean streams raises major challenges caused by the need to fix different problems related to poor catalyst activity and to urea injection handling. In this respect, an important issue is related to the presence of unburned hydrocarbons (HCs) in the exhausts that may damage irreversibly the activity of the DeNOx catalysts. The purpose of the present perspective is to summarize the most important effects of HCs on NH3-SCR performances of commercial SCR catalysts, as well as to present a comprehensive inventory of available kinetic models. In particular, the following main aspects will be discussed, according to recent literature indications: (i) competitive adsorption between HC and NH3; (ii) effect of the zeolite structure on HC deactivation; (iii) potential formation of surface intermediates and active site blocking; (iv) pore physical blocking due to large HC molecules or coke formation; (v) possible parasitic reactions between HCs and SCR reagents; vi) description of the available kinetic models able to account for these effects; and vii) design of improved catalysts with enhanced hydrocarbon poisoning resistance
Abgasnachbehandlungseinrichtung für ein Kraftfahrzeug mit einem Katalysator, welcher wenigstens ein SCR-Material und wenigstens ein NOx-Speicher-Material aufweist, und Verfahren zum Betreiben einer solchen Abgasnachbehandlungseinrichtung
No full textUnexpected Low-Temperature deNOx Activity of AdSCR Systems for Cold Start NOx Abatement
No full textLow-temperature operation of urea selective catalytic reduction (SCR) aftertreatment systems for the abatement of NOx from diesel engines presents new challenges related to poor catalytic activity and the urea injection temperature threshold. Physical mixtures of a NH3-SCR catalyst (e.g., Fe-/Cu-zeolite) and of a NOx storage material (e.g., BaO/Al2O3, CeO2/Al2O3) have shown promising performances in terms of overall NOx removal efficiency, as they can operate both as NOx adsorbers, trapping NOx during the cold start transient, and as SCR catalysts, reducing at higher temperatures the previously stored NOx with NH3. Herein, we extend the investigation of new Cu-CHA + BaO/Al2O3 AdSCR systems (AdSCR = adsorption + selective catalytic reduction) focusing on the reactivity between NOx and ammonia in the low-temperature window (from room temperature up to 170 °C). We find that the selective reduction of NO by NH3 over Cu-CHA is surprisingly enhanced by the presence of BaO/Al2O3 when ammonia is preadsorbed, leading to the onset of nitrogen formation already at 40 °C
Analysis of AdSCR Systems for NOx Removal During the Cold-Start Period of Diesel Engines
No full textHerein, we extend the study of the AdSCR system (AdSCR = adsorption + selective catalytic reduction), consisting in a physical mixture of a conventional NH3-SCR catalyst and of a NOx storage material. We have shown in previous work that an AdSCR system can capture and store NOx at room temperature from Diesel engine exhausts, and directly reduce them with ammonia at higher temperatures in the same unit. The present work aims at optimizing the system composition, in order to minimize the release of NOx in the low temperature window. Results from cold start mimicking experiments show that the full storage time, i.e. the zero-emission period where the fed NO is completely adsorbed by the catalyst, is affected only by the amount and the composition of the storage material, whereas the NOx storage efficiency is controlled by amount and nature of both components of the physical mixture
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
[Newspaper Clipping: Author Claims Evidence of Second JFK Assassin #1]
No full textNewspaper article titled "Author Claims Evidence of Second JFK Assassin." The article states that author Richard J. Whalen concluded "that there is circumstantial evidence to support the theory of a second assassin in the shooting of President John F. Kennedy.
Also By The Same Author: AKTiveAuthor, a Citation Graph Approach to Name Disambiguation
No full textThe desire for definitive data and the semantic web drive for inference over heterogeneous data sources requires co-reference resolution to be performed on those data. In particular, name disambiguation is required to allow accurate publication lists, citation counts and impact measures to be determined. This paper describes a graph-based approach to author disambiguation on large-scale citation networks. Using self-citation, co-authorship and document source analyses, AKTiveAuthor clusters papers, achieving precision of 0.997 and recall of 0.818 over a test group of eight surname clusters
John F. Kennedy telegram to Roosevelt
No full textJersey Homesteads (later the Borough of Roosevelt) was established in the 1930s as an agro-industrial cooperative community. It was established specifically for urban Jewish garment workers, many of whom had emigrated from Europe. President John F. Kennedy sent a telegram to the citizens of Roosevelt, New Jersey, apologizing for not being able to attend the memorial dedication in honor of former President Franklin Delano Roosevelt. (Jersey Homesteads became Roosevelt in 1945 in honor of the president.) President Kennedy expressed his gratitude to the people of Roosevelt for constructing the memorial, and commented that it will serve as a constant reminder of Roosevelt's good works
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