Quantum Chemical Simulation of NO Reduction by Ammonia (SCR Reaction) on V2O5 Catalyst Surface PDF Download

Author: Alper Uzun
Publisher:
ISBN:
Category : Density functionals
Languages : en
Pages : 142

View

Book Description

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
The reaction mechanism for the selective catalytic reduction (SCR) of nitric oxide by ammonia on (010) V2O5 surface represented by a V2O9H8 cluster was simulated by density functional theory (DFT) calculations. The computations indicated that SCR reaction consisted of three main parts. In the first part ammonia activation on Brønsted acidic V-OH site as NH4+ species by a nonactivated process takes place. The second part includes the interaction of NO with pre-adsorbed NH4 + species to eventually form nitrosamide (NH2NO). The rate limiting step for this part as well as for the total SCR reaction is identified as NH3NHO formation reaction. The last part consists of the decomposition of NH2NO on the cluster which takes advantage of a hydrogen transfer mechanism between the active V=O and V-OH groups. Water and ammonia adsorption and dissociation are investigated on (101) and (001) anatase surfaces both represented by totally fixed and partially relaxed Ti2O9H10 clusters. Adsorption of H2O and NH3 by H-bonding on previously H2O and NH3 dissociated systems are also considered. By use of a (001) relaxed Ti2O9H10 cluster, the role of anatase support on SCR reaction is investigated. Since NH2NO formation on Ti2O9H10 cluster requires lower activation barriers than on V2O5 surface, it is proposed that the role of titanium dioxide on SCR reaction could be forming NH2NO. The role of vanadium oxide is crucial in terms of dissociating this product into H2O and N2. Finally, NH3 adsorption is studied on a V2TiO14H14 cluster which represents a model for vanadia/titania surface.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 10

View

Book Description
We compared the molecular structures, surface acidity and catalytic activity for NO/NH3/O2 SCR of V2O5-WO3/TiO2 catalysts for two different synthesis methods: co-precipitation of aqueous vanadium and tungsten oxide precursors with TiO(OH)2 and by incipient wetness impregnation of the aqueous precursors on a reference crystalline TiO2 support (P25; primarily anatase phase). Bulk analysis by XRD showed that co-precipitation results in small and/or poorly ordered TiO2(anatase) particles and that VOx and WOx do not form solid solutions with the bulk titania lattice. Surface analysis of the co-precipitated catalyst by High Sensitivity-Low Energy Ion Scattering (HS-LEIS) confirms that the VOx and WOx are surface segregated for the co-precipitated catalysts. In situ Raman and IR spectroscopy revealed that the vanadium and tungsten oxide components are present as surface mono-oxo O = VO3 and O = WO4 sites on the TiO2 supports. Co-precipitation was shown for the first time to also form new mono-oxo surface VO4 and WO4 sites that appear to be anchored at surface defects of the TiO2 support. IR analysis of chemisorbed ammonia showed the presence of both surface NH3* on Lewis acid sites and surface NH4+* on Brønsted acid sites. TPSR spectroscopy demonstrated that the specific SCR kinetics was controlled by the redox surface VO4 species and that the surface kinetics was independent of TiO2 synthesis method or presence of surface WO5 sites. SCR reaction studies revealed that the surface WO5 sites possess minimal activity below ~325 °C and their primary function is to increase the adsorption capacity of ammonia. A relationship between the SCR activity and surface acidity was not found. The SCR reaction is controlled by the surface VO4 sites that initiate the reaction at ~200 °C. The co-precipitated catalysts were always more active than the corresponding impregnated catalysts. Finally, we ascribe the higher activity of the co-precipitated catalysts to the presence of the new surface WOx sites associated surface defects on the TiO2 support that increase the ammonia adsorption capacity.

Author: Ewa Broclawik
Publisher: Springer
ISBN: 3030117146
Category : Science
Languages : en
Pages : 532

View

Book Description
This book focuses on the electronic properties of transition metals in coordination environments. These properties are responsible for the unique and intricate activity of transition metal sites in bio- and inorganic catalysis, but also pose challenges for both theoretical and experimental studies. Written by an international group of recognized experts, the book reviews recent advances in computational modeling and discusses their interplay using experiments. It covers a broad range of topics, including advanced computational methods for transition metal systems; spectroscopic, electrochemical and catalytic properties of transition metals in coordination environments; metalloenzymes and biomimetic compounds; and spin-related phenomena. As such, the book offers an invaluable resource for all researchers and postgraduate students interested in both fundamental and application-oriented research in the field of transition metal systems.

Author: Isabella Nova
Publisher: Springer Science & Business Media
ISBN: 1489980717
Category : Science
Languages : en
Pages : 715

View

Book Description
Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts presents a complete overview of the selective catalytic reduction of NOx by ammonia/urea. The book starts with an illustration of the technology in the framework of the current context (legislation, market, system configurations), covers the fundamental aspects of the SCR process (catalysts, chemistry, mechanism, kinetics) and analyzes its application to useful topics such as modeling of full scale monolith catalysts, control aspects, ammonia injections systems and integration with other devices for combined removal of pollutants.

Author: Mònica Calatayud
Publisher:
ISBN:
Category :
Languages : en
Pages : 68

View

Book Description

Author: Giriraj Sharma
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
In this work, the steady-state performance of zeolite-based Cu-ZSM-5, vanadium based honeycomb monolith catalysts (V), vanadium-titanium based pillared inter layered clay catalyst (V-Ti PLIC) and vanadium-titanium-tungsten-based honeycomb monolith catalysts (V-Ti-W) was investigated in the selective catalytic reduction process (SCR) for NO removal using NH3 in presence of oxygen. The objective is to obtain the expression that would predict the conversion performance of the catalysts for different values of the SCR process parameters, namely temperature, inlet oxygen concentration and inlet ammonia concentration. The NO[subscript]x emission, its formation and control methods are discussed briefly and then the fundamentals of the SCR process are described. Heat transfer based and chemical kinetics based SCR process models are discussed and widely used rate order based model are reviewed. Based on the experimental data, regression analysis was performed that gives an expression for predicting the SCR rate for the complete temperature range and the rate order with respect to inlet oxygen and ammonia concentration. The average activation energy for the SCR process was calculated and optimum operating conditions were determined for each of the catalyst. The applicable operating range for the catalyst depends on the NO conversion as well as on the ammonia slip and the N2O and NO2 emission. The regression analysis was repeated for the applicable range and an expression was obtained that can be used to estimate the catalyst performance. For the Cu-ZSM-5, the best performance was observed for 400°C, 660 ppm inlet ammonia concentration and 0.1% inlet oxygen concentration. For the V based honeycomb monolith catalyst, the best performance was observed for 300°C, 264 ppm inlet ammonia concentration and 3% inlet oxygen concentration. For the V-Ti based PLIC catalyst, the best performance was observed for 350°C, 330 ppm inlet ammonia concentration and 3% inlet oxygen concentration. For the V-Ti-W based honeycomb monolith catalyst, the best performance was observed for 300°C, 330 ppm inlet ammonia concentration and 3% inlet oxygen concentration. The conversion performance of all of these catalysts is satisfactory for the industrial application. At the operating conditions listed above, the N2O emission is less than 20 ppm and the NO2 emission is less than 10 ppm. The results were validated by comparing the findings with the similar work by other research groups. The mechanism of SCR process is discussed for each of the catalyst. The probable reactions are listed and adsorption and desorption process are studied. The various mechanisms proposed by the researchers are discussed briefly. It is concluded that V-Ti-W and Cu-ZSM-5 catalyst are very promising for SCR of NO[subscript]x. The expressions can be used to estimate the conversion performance and can be utilized for optimal design and operation. The expressions relate the SCR rate to the input parameters such as temperature and inlet oxygen and ammonia concentration hence by controlling these parameters desired NO[subscript]x reduction can be achieved with minimal cost and emission.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
As lean-burn engines are being introduced in the United States, both advantages and disadvantages arise. Lean-burn engines can operate at a high efficiency, and are developed for a wide range of power supplies. Unfortunately, due to the low temperature at which these engines operate, NO[subscript x] formation becomes an issue. Forthcoming legislation pertaining to heavy-duty lean-burn engines aimed at reducing both particulate matter emissions and emissions of nitric oxides has brought about a need for a better method for reducing NO[subscript x] from lean exhaust gases at moderate temperatures. It is generally accepted that current fuel treatment processes alone will be unable to accommodate emission standards proposed for upcoming years. While the current 3-way catalyst is ineffective in reducing NO[subscript x] under lean conditions, many new strategies are being developed. The Lean NO[subscript x] Catalyst (LNC), Lean NO[subscript x] Trap (LNT), and Selective Catalytic Reduction (SCR) catalyst are all viable methods with research underway. Currently, the selective catalytic reduction (SCR) of nitrogen oxides by N-containing reducing agents is one of the most powerful methods for accomplishing the removal of NO[subscript x] from an exhaust stream. This technology has been in place in steady state power plants, but has yet to be fully implemented in mobile engines. This is due in part to the problems encountered in the automated control of ammonia addition to the exhaust gas. In steady state operation, a relatively constant amount of NO[subscript x] is produced over a given amount of time. Thus, to provide a stoichiometric amount of ammonia only the steady state concentration of NO[subscript x] must be known. In an automotive application the NO[subscript x] produced is not constant and the addition of ammonia must vary accordingly. The purpose of this thesis is to explore the SCR process of the reaction between NO and NH3 through an experimental matrix and also through a kinetic study extracted from the results. These results are used in a simple theoretical model of the SCR reaction. The use of NO as the only form of NO[subscript x] allows for the kinetics of the NO reaction to be studied separately from the NO2 kinetics. This will be a first step in understanding the overall SCR process involving both NO and NO2. The SCR process for the reaction between NO and NH3, while understood on a global scale, is still under debate at the elementary level. It is currently thought that the reaction occurs according to an Eley-Rideal mechanism, where strongly absorbed ammonia reacts with weakly absorbed or gas phase NO to produce nitrogen and water. It is generally accepted that this reaction proceeds in first order with respect to nitric oxide and zero order with respect to ammonia and oxygen.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 77

View

Book Description
The most advanced and proven technology for NO(subscript x) control for stationary sources is Selective Catalytic Reduction (SCR). In SCR, NO(subscript x) is reduced by NH3 to N2 and H2O. The commercial catalysts are based on V2O5/TiO2, and the vanadium-based catalysts are patented by the Japanese (Mitsubishi). However, there are three main advantages for the vanadium-based SCR catalyst: (a) a tendency to be poisoned in the flue gas; (b) oxidation of SO2 to SO3 by V2O5, this is a particularly severe problem due to the higher sulfur content of American coals compared with coals used in Japan (from Australia) and in Europe; (c) environmental problems involved in the disposal of the spent catalyst (due to the toxicity of vanadium). In order to overcome these problems, in addition to the undesirable dominance by the Japanese patent position, the authors have studied in this project a new type of catalyst for the SCR reaction; namely, pillared clays, which have adjustable, unique structures and acidity. Three types of catalysts were developed and tested for this reaction, i.e. Fe2O3-pillared clays, delaminated Fe2O3-pillared clays, and ion-exchanged pillared clays. The project was divided into sixteen tasks, and will be reported as such.

Author: Oliver Kröcher
Publisher:
ISBN: 9783038973652
Category :
Languages : en
Pages :

View

Book Description
The most efficient process to reduce NOx emissions from lean exhaust gases, selective catalytic reduction (SCR) with ammonia, has undergone tremendous development over the past decades. Originally only applied in stationary power plants and industrial installations, SCR systems are now installed in millions of mobile diesel engines, ranging from off-road machineries, to heavy-duty and light-duty trucks and passenger cars, to locomotives and ships. All of these applications involve specific challenges due to tighter emission limits, new internal combustion engine technologies, or alternative fuels. Three review articles and 14 research articles in this book describe recent results and research trends of various aspects of the SCR process. Reaction engineering aspects, such as the proper dosage of ammonia or urea, respectively, are as important as further developments of the different SCR catalysts, by deepening the understanding of their functionality or by systematic improvements of their properties, such as low-temperature activity, selectivity, or poisoning-resistance. Another covered aspect is cost reduction through the use of cheaper base materials for the production is active and stable SCR catalysts. Finally, research efforts are reported to develop SCR processes with different reducing agents, which would open doors to new applications in the future. The range of topics addressed in this book will stimulate the reader's interest as well as provide a valuable source of information for researchers in academia and industry.