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Author: Publisher: ISBN: Category : Languages : en Pages : 4
Book Description
Currently CARB estimates on road diesel vehicles contribute 50% of the NOX and 78% of the particulates being discharged from mobile sources. Diesel emissions obviously must be reduced if future air quality targets are to be met. A critical technological barrier exists because there are no commercial technologies available, which can reduce NOX from diesel (lean), exhaust containing 5-15% O2 concentration. One promising approach to reducing NOX and particulates from diesel exhaust is to use a combination of plasma with catalyst. Plasma can be generated thermally or non-thermally. Thermal plasma is formed by heating the system to an exceedingly high temperature (>2000 C). High temperature requirements for plasma makes thermal plasma inefficient and requires skillful thermal management and hence is considered impractical for mobile applications. Non-thermal plasma directs electrical energy into the creation of free electrons, which in turn react with gaseous species thus creating plasma. A combination of non-thermal plasma with catalysts can be referred to Plasma Assisted Catalysts or PAC. PAC technology has been demonstrated in stationary sources where non-thermal plasma catalysis is carried out in presence of NH3 as a reductant. In stationary applications NO is oxidized to HNO3 and then into ammonium nitrate where it is condensed and removed. This approach is impractical for mobile application because of the ammonia requirement and the ultimate mechanism by which NOX is removed. However, if a suitable catalyst can be found which can use onboard fuel as reductant then the technology holds a considerable promise. NOX REDUCTION FOR LEAN EXHAUST USING PLASMA ASSISTED CATALYSIS Ralph Slone, B. Bhatt and Victor Puchkarev NOXTECH INC. In addition to the development of an effective catalyst, a non-thermal plasma reactor needs be scaled and demonstrated along with a reliable and cost effective plasma power source and onboard HC source needs to be proven. Under the work sponsored by DOE and SCAQMD Noxtech is developing a cost effective and reliable PAC system for mobile applications. The goal of the program is to develop a suitable catalyst with the ability to remove high levels of NOx at reasonable space velocities. This new catalyst will then be used to scale the technology to treat exhaust from 80Hp engine and eventually to demonstrate the technology on 200 and 400 Hp engine applications. Using the 2004 EPA proposed regulation as a standard, it is clear in order for PAC system to be commercially viable it needs to remove NOX by 70% or better. It is further assumed from past experience that 30,000 HR-1 space velocities are necessary to ensure a good compact design.
Author: Publisher: ISBN: Category : Languages : en Pages : 4
Book Description
Currently CARB estimates on road diesel vehicles contribute 50% of the NOX and 78% of the particulates being discharged from mobile sources. Diesel emissions obviously must be reduced if future air quality targets are to be met. A critical technological barrier exists because there are no commercial technologies available, which can reduce NOX from diesel (lean), exhaust containing 5-15% O2 concentration. One promising approach to reducing NOX and particulates from diesel exhaust is to use a combination of plasma with catalyst. Plasma can be generated thermally or non-thermally. Thermal plasma is formed by heating the system to an exceedingly high temperature (>2000 C). High temperature requirements for plasma makes thermal plasma inefficient and requires skillful thermal management and hence is considered impractical for mobile applications. Non-thermal plasma directs electrical energy into the creation of free electrons, which in turn react with gaseous species thus creating plasma. A combination of non-thermal plasma with catalysts can be referred to Plasma Assisted Catalysts or PAC. PAC technology has been demonstrated in stationary sources where non-thermal plasma catalysis is carried out in presence of NH3 as a reductant. In stationary applications NO is oxidized to HNO3 and then into ammonium nitrate where it is condensed and removed. This approach is impractical for mobile application because of the ammonia requirement and the ultimate mechanism by which NOX is removed. However, if a suitable catalyst can be found which can use onboard fuel as reductant then the technology holds a considerable promise. NOX REDUCTION FOR LEAN EXHAUST USING PLASMA ASSISTED CATALYSIS Ralph Slone, B. Bhatt and Victor Puchkarev NOXTECH INC. In addition to the development of an effective catalyst, a non-thermal plasma reactor needs be scaled and demonstrated along with a reliable and cost effective plasma power source and onboard HC source needs to be proven. Under the work sponsored by DOE and SCAQMD Noxtech is developing a cost effective and reliable PAC system for mobile applications. The goal of the program is to develop a suitable catalyst with the ability to remove high levels of NOx at reasonable space velocities. This new catalyst will then be used to scale the technology to treat exhaust from 80Hp engine and eventually to demonstrate the technology on 200 and 400 Hp engine applications. Using the 2004 EPA proposed regulation as a standard, it is clear in order for PAC system to be commercially viable it needs to remove NOX by 70% or better. It is further assumed from past experience that 30,000 HR-1 space velocities are necessary to ensure a good compact design.
Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Recent developments in catalytic control of NOx are revealing the significance of NO2 as an intermediary for achieving higher NOx removal efficiencies. This paper discusses the combination of the plasma with a catalyst to improve the selective reduction of NOx under lean-burn conditions. It is shown that the main effect of the plasma is to enhance the gas-phase oxidation of NO to NO2. The reduction of NOx to N2 is then accomplished by the heterogeneous reaction of NO2 with activated hydrocarbons on the catalyst surface. By using a plasma, one can take advantage of a new class of catalysts that are potentially more durable, more active, more selective and more sulfur-tolerant compared to conventional lean-NOx catalysts. The plasma-assisted catalytic reduction process can be implemented with any type of plasma reactor and does not require a specific type of electrical power supply. It can also easily accommodate any type of catalyst support structure.
Author: B. Penetrante Publisher: ISBN: Category : Languages : en Pages : 5
Book Description
Recent Studies suggest that the conversion of NO to NO2 is an important intermediate step in the selective catalytic reduction (SCR) of NOx to N2. These studies have prompted the development of schemes that use an oxidation catalyst to convert NO to NO2, followed by a reduction catalyst to convert NO2 to N2. Multi-stage SCR offers high NOx reduction efficiency from catalysts that, separately, are not very active for reduction of NO, and alleviates the problem of selectivity between NO reduction and hydrocarbon oxidation. A plasma can also be used to oxidize NO to NO2. This paper compares the multi-stage catalytic scheme with the plasma-assisted catalytic scheme for reduction of NOx in lean-burn engine exhausts. The advantages of plasma oxidation over catalytic oxidation are presented.
Author: Publisher: ISBN: Category : Languages : en Pages : 6
Book Description
The control of NOx (NO and NO2) emissions from so-called ''lean-burn'' vehicle engines remains a challenge. In recent years, there have been a number of reports that show that a plasma device combined with a catalyst can reduce as high as 90% or more of NOx in simulated diesel and other ''lean-burn'' exhaust. In the case of propylene containing simulated diesel exhaust, the beneficial role of a plasma treatment is now thought to be due to oxidation of NO to NO2, and the formation of partially oxidized hydrocarbons that are more active for the catalytic reduction of NO2 than propylene. Thus, the overall system can be most usefully described as hydrocarbon selective catalytic reduction (SCR) enhanced by 'reforming' the exhaust with a non-thermal plasma (NTP) device. For plasma-enhanced catalysis, both zeolite- and alumina-based materials have shown high activity, albeit in somewhat different temperature ranges, when preceded by an NTP reactor. This paper will briefly describe our research efforts aimed at optimizing the catalyst materials for NTP-catalysis devices based, in part, on our continuing studies of the NTP- and catalytic-reaction mechanisms. Various alkali- and alkaline earth-cation-exchanged Y zeolites have been prepared, their material properties characterized, and they have been tested as catalytic materials for NOx reduction in laboratory NTP-catalysis reactors. Interestingly, NO2 formed in the plasma and not subsequently removed over these catalysts, will back-convert to NO, albeit to varying extents depending upon the nature of the cation. Besides this comparative reactivity, we will also discuss selected synthesis strategies for enhancing the performance of these zeolite-based catalyst materials. A particularly important result from our mechanistic studies is the observation that aldehydes, formed during the plasma treatment of simulated diesel exhaust, are the important species for the reduction of NOx to N2. Indeed, acetaldehyde has been found to be especially effective in the thermal reduction of both NO and NO2 over Ba- and Na-Y zeolite catalysts.
Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Many studies suggest that lean-NOx SCR proceeds via oxidation of NO to NO2 by oxygen, followed by the reaction of the NO2 with hydrocarbons. On catalysts that are not very effective in catalyzing the equilibration of NO+O2 and NO2, the rate of N2 formation is substantially higher when the input NOx is NO2 instead of NO. The apparent bifunctional mechanism in the SCR of NOx has prompted the use of mechanically mixed catalyst components, in which one component is used to accelerate the oxidation of NO to NO2, and another component catalyzes the reaction between NO2 and the hydrocarbon. Catalysts that previously were regarded as inactive for NOx reduction could therefore become efficient when mixed with an oxidation catalyst. Preconverting NO to NO2 opens the opportunity for a wider range of SCR catalysts and perhaps improves the durability of these catalysts. This paper describes the use of a non-thermal plasma as an efficient means for selective partial oxidation of NO to NO2. When combined with some types of SCR catalyst, the plasma can greatly enhance the NOx reduction and eliminate some of the deficiencies encountered in an entirely catalyst-based approach.
Author: Publisher: ISBN: Category : Languages : en Pages : 8
Book Description
Lean burn gasoline and diesel engines provide improved fuel economy when compared to engines operating under stoichiometric fuel/air conditions. At the same time, lean burn and diesel engines present a problem for emission control. Because they operate under oxidizing conditions, the conventional three-way catalyst is not effective in NOx reduction [1,2]. In addition, the wide temperature range of automobile exhaust gases present a challenge for catalyst design. The temperature of exhaust gases from a light duty diesel engine can vary from 150 to 500 C, depending on the operating conditions. To date, a catalyst that operates with high NOx conversion efficiency over the entire operating range has not been found. Non-thermal plasma assisted catalysis has been shown to be a promising technology for NOx reduction in lean burn and diesel exhaust gases [3,4]. The approach exploited in this paper is to use a plasma in combination with several catalysts, each of which are active over unique temperature ranges. It was reported in the literature, that the one of the essential roles of plasma treatment is to oxidize NO to easier reducible NO2 [7]. In this contribution, the other important function of plasma treatment, namely partial oxidation of propylene, will be demonstrated.
Author: Xin Tu Publisher: Springer Nature ISBN: 3030051897 Category : Science Languages : en Pages : 354
Book Description
This book provides a comprehensive overview of the field of plasma catalysis, regarded as a promising alternative to thermal processes for energy and environmental applications. It bridges the gap between the plasma and catalysis research communities, covering both the fundamentals of plasma catalysis and its application in environmental and energy research. The first section of the book offers a broad introduction to plasma catalysis, covering plasma-catalyst systems, interactions, and modeling. The core of the book then focuses on different applications, describing a wide range of plasma-catalytic processes in catalyst synthesis, environmental clean-up, greenhouse gas conversion and synthesis of materials for energy applications. Chapters cover topics ranging from removal of NOx and VOCs to conversion of methane, carbon dioxide and the reforming of ethanol and methanol. Written by a group of world-leading researchers active in the field, the book forms a valuable resource for scientists, engineers and students with different research backgrounds including plasma physics, plasma chemistry, catalysis, energy, environmental engineering, electrical engineering and material engineering.
Author: Publisher: ISBN: Category : Languages : en Pages : 6
Book Description
The widespread use of light duty diesel engines in the United States would naturally lead to a large reduction of fuel consumption, due to their generally higher efficiency. By extension, savings in fuel consumption would decrease the total CO2 emitted from mobile sources. Although this is a desirable goal, at present a major stumbling block to increased diesel engine use is the difficulty in reducing noxious exhaust components, mainly NOx and particulates, to acceptable levels. We are studying the possibility of reducing NOx emissions through the combination of non-thermal plasma with appropriate catalysts. The broad outline of how this technique works has been worked out both experimentally and theoretically. 1-3 The presently accepted model is that a non-thermal plasma in the presence of water, oxygen and hydrocarbon will efficiently convert NO to NO2, while only partially oxidizing the hydrocarbon present. Some catalysts will reduce NO2 (but not necessarily NO) i n the presence of excess oxygen if the proper hydrocarbon is present. In this paper we report results using non-thermal plasma in conjunction with a commonly available zeolite catalyst, NaY, to treat synthetic diesel exhaust. We focus on details of the heterogeneous chemistry on NaY by comparing the thermal and plasma driven chemistry. EXPERIMENT Details of our experiment have been published elsewhere, so only a brief summary is included here. 4 Synthetic exhaust gas was created by blending gases from cylinders of known composition using mass flow controllers. Besides NO, the exhaust mixture included CO, CO2, propylene, water, oxygen and nitrogen. A typical mixture contained 6% oxygen, 2% water, and, unless otherwise noted, a 3:1 ratio of propylene to NOx. This corresponds to a 9:1 ratio on a C1 basis. CO and CO2 were sometimes included, but we found that their presence did not materially affect our results. For nitrogen balance experiments we omitted CO and CO2 and replaced the nitrogen bath gas with helium.
Author: Publisher: ISBN: Category : Languages : en Pages : 2
Book Description
Progress has been made in the control of combustion processes to limit the formation of environmentally harmful species, but lean burn vehicles, such as those powered by diesel engines used for the majority of commercial trucking and off-road applications, remain a major source of nitrogen oxides (NOx) and particulate matter (PM) emissions. Tighter control of the combustion process coupled with exhaust gas recirculation has brought emissions in line with 2004 targets worldwide. Additional modifications to the engine control system, somewhat limited NOx control, and PM filters will likely allow the 2007 limits to be met for the on-highway regulations for heavy-duty engines in the United States. Concern arises when the NOx emission limit of 0.2 g/bhphr set for the year 2010 is considered.
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