Identification of copper species present in Cu-ZSM-5 catalysts for NOx reduction

The structure of Cu-ZSM-5 catalysts that show activity for direct NO decomposition and selective catalytic reduction of NOx by hydrocarbons has been investigated by a multitude of modern surface analysis and spectroscopy techniques including X-ray photoelectron spectroscopy, thermogravimetric analysis, and in situ Fourier transform infrared spectroscopy. A series of four catalysts were prepared by exchange of Na-ZSM-5 with dilute copper acetate, and the copper loading was controlled by variation of the solution pH. Underexchanged catalysts contained isolated Cu2+OH-(H2O) species and as the copper loading was increased Cu2+ ions incorporated into the zeolite lattice appeared. The sites at which the latter two copper species were located were fundamentally different. The Cu2+OH-(H2O) moieties were bound to two lattice oxygen ions and associated with one aluminum framework species. In contrast, the Cu2+ ions were probably bound to four lattice oxygen ions and associated with two framework aluminum ions. Once the Cu-ZSM-5 samples attained high levels of exchange, the development of [Cu(μ-OH)2Cu]n2+OH-(H2O) species along with a small concentration of Cu(OH)2 was observed. On activation in helium to 500°C the Cu2+OH-(H2O) species transformed into Cu2+O- and Cu+ moieties, whereas the Cu2+ ions were apparently unaffected by this treatment (apart from the loss of ligated water molecules). Calcination of the precursors resulted in the formation of Cu2+O2- and a one-dimensional CuO species. Temperature-programmed desorption studies revealed that oxygen was removed from the latter two species at 407 and 575°C, respectively. © 1999 Academic Press.

The role of non-thermal plasma technique in {NOx} treatment: A review

Non-thermal plasma (NTP) has been introduced over the past several years as a promising method for nitrogen oxide (NOx) removal. The intent, when using NTP, is to selectively transfer input electrical energy to the electrons, and to not expend this in heating the entire gas stream, which generates free radicals through collisions, and promotes the desired chemical changes in the exhaust gases. The generated active species react with the pollutant molecules and decompose them. This paper reviews and summarizes relevant literature regarding various aspects of the application of {NTP} technology on {NOx} removal from exhaust gases. A comprehensive description of available scientific literature on {NOx} removal using {NTP} technology is presented, including various types of NTP, e.g. dielectric barrier discharge, corona discharge and electron beam. Furthermore, the combination of {NTP} with catalyst and adsorbent for better {NOx} removal efficiency is presented in detail. The removal of {NOx} from both simulated gases and real diesel engines is also considered in this review paper. As {NTP} is a new technique and is not yet commercialized, there is a need for more studies to be performed in this field.

Load-Commutated SCR Current-Source-Inverter-Fed Induction Motor Drive With Sinusoidal Motor Voltage and Current

Current source inverter (CSI) is an attractive solution in high-power drives. The conventional gate turn-off thyristor (GTO) based CSI-fed induction motor drives suffer from drawbacks such as low-frequency torque pulsation, harmonic heating, and unstable operation at low-speed ranges. These drawbacks can be overcome by connecting a current-controlled voltage source inverter (VSI) across the motor terminal replacing the bulky ac capacitors. The VSI provides the harmonic currents, which results in sinusoidal motor voltage and current even with the CSI switching at fundamental frequency. This paper proposes a CSI-fed induction motor drive scheme where GTOs are replaced by thyristors in the CSI without any external circuit to assist the turning off of the thyristors. Here, the current-controlled VSI, connected in shunt, is designed to supply the volt ampere reactive requirement of the induction motor, and the CSI is made to operate in leading power factor mode such that the thyristors in the CSI are autosequentially turned off. The resulting drive will be able to feed medium-voltage, high-power induction motors directly. A sensorless vector-controlled CSI drive based on the proposed configuration is developed. The experimental results from a 5 hp prototype are presented. Experimental results show that the proposed drive has stable operation throughout the operating range of speeds.

NOx Reduction and Desorption Studies Under Electric Discharge Plasma Using a Simulated Gas Mixture: A Case Study on the Effect of Corona Electrodes

In this study, reduction and desorption of oxides of nitrogen (NOx) were conducted using an electrical discharge plasma technique. The study was carried out using a simulated gas mixture to explore the possibility of re-generation of used adsorbents by a nonthermal plasma desorption technique. Three different types of corona electrodes, namely, pipe, helical wire, and straight wire, were used for analyzing their effectiveness in NOx reduction/desorption. The pipe-type corona electrode exhibited a nitric oxide (NO) conversion of 50%, which is 1.5 times that of the straight-wire-type electrode at an energy density of 175J/L. The helical-wire-type corona electrode exhibited a NOx desorption efficiency almost 4 times that of the pipe-type electrode,indicating the possibility that corona-generated species play a crucial role in desorption.

Catalysis for NOx abatement

Research in the field of NOx abatement has grown significantly in the past two decades. The general trend has been to develop new catalysts with complex materials in order to meet the stringent environmental regulations. This review discusses briefly about the different sources of NOx and its adverse effect on the ecosystem. The main portion of the review discusses the progress and development of various catalysts for NOx removal from exhaust by NO decomposition, NO reduction by CO or H-2 or NH3 or hydrocarbons. The importance of understanding the mechanism of NO decomposition and reduction in presence of metal ion substituted catalysts is emphasized. Some conclusions are made on the various catalytic approaches to NOx abatement.

Observations of production and transport of NOx formed by energetic particle precipitation in the polar night atmosphere

This work is focused on the effects of energetic particle precipitation of solar or magnetospheric origin on the polar middle atmosphere. The energetic charged particles have access to the atmosphere in the polar areas, where they are guided by the Earth's magnetic field. The particles penetrate down to 20-100 km altitudes (stratosphere and mesosphere) ionising the ambient air. This ionisation leads to production of odd nitrogen (NOx) and odd hydrogen species, which take part in catalytic ozone destruction. NOx has a very long chemical lifetime during polar night conditions. Therefore NOx produced at high altitudes during polar night can be transported to lower stratospheric altitudes. Particular emphasis in this work is in the use of both space and ground based observations: ozone and NO2 measurements from the GOMOS instrument on board the European Space Agency's Envisat-satellite are used together with subionospheric VLF radio wave observations from ground stations. Combining the two observation techniques enabled detection of NOx enhancements throughout the middle atmosphere, including tracking the descent of NOx enhancements of high altitude origin down to the stratosphere. GOMOS observations of the large Solar Proton Events of October-November 2003 showed the progression of the SPE initiated NOx enhancements through the polar winter. In the upper stratosphere, nighttime NO2 increased by an order of magnitude, and the effect was observed to last for several weeks after the SPEs. Ozone decreases up to 60 % from the pre-SPE values were observed in the upper stratosphere nearly a month after the events. Over several weeks the GOMOS observations showed the gradual descent of the NOx enhancements to lower altitudes. Measurements from years 2002-2006 were used to study polar winter NOx increases and their connection to energetic particle precipitation. NOx enhancements were found to occur in a good correlation with both increased high-energy particle precipitation and increased geomagnetic activity. The average wintertime polar NOx was found to have a nearly linear relationship with the average wintertime geomagnetic activity. The results from this thesis work show how important energetic particle precipitation from outside the atmosphere is as a source of NOx in the middle atmosphere, and thus its importance to the chemical balance of the atmosphere.

Cascaded Cross Flow DBD-Adsorbent Technique for NOX Abatement in Diesel Engine Exhaust

In this paper, a different type of cross flow dielectric barrier discharge (DBD) reactor was designed and tested. Here the gas flow is perpendicular to the barrier discharge electrode. Discharge plasma was utilized to oxidize NO contained in the exhaust gas to NO2 and subsequent NO2 removal can be improved using an adsorbent system. A detailed study of DeNO(X) in a stationary diesel engine exhaust was carried out using pulsed electrical discharges/adsorbent processes. Activated alumina (Al2O3) and MS-13x were used as adsorbents at room temperature. The main emphasis is laid on the removal of NOX from the filtered diesel engine exhaust. In filtered exhaust environment, the cross flow reactor along with adsorbent exhibits a superior performance with regard to NOX removal when compared to that with axial flow of gas. In this paper we bring out a relative comparison of discharge plasma and plasma-adsorbent process at various gas flow rates, ranging from 2 l/min to 25 l/min. The discharge plasma-adsorbent assisted barrier discharge reactor has shown promising results in NOX removal at high flow rates.

Study of Pulsed Plasma in a Crossed Flow Dielectric Barrier Discharge Reactor for Improvement of NOx Removal in Raw Diesel Engine Exhaust

Improved performance of plasma in raw engine exhaust treatment is reported. A new type of reactor referred to as of cross-flow dielectric barrier discharge (DBD) was used, in which the gas flow is perpendicular to the corona electrode. In raw exhaust environment, the cross-flow (radial-flow) reactor exhibits a superior performance with regard to NOX removal when compared to that with axial flow of gas. Experiments were conducted at different flow rates ranging from 2 L/min to 25 L/min. The plasma assisted barrier discharge reactor has shown encouraging results in NOx removal at high flow rates.

Studies on Compact Discharge Plasma Source for NOX Treatment in Engine Exhaust

This paper proposes a compact electric discharge plasma source for controlling NOX emission in diesel engine exhaust. An automobile ignition coil was used to generate the high voltage pulse using flyback topology. This design is aimed at retrofitting the existing catalytic converters with pulse assisted cleaning technique. In this paper we bring out a relative comparison of discharge plasma and plasma-adsorbent process at different gas flow rates. Activated alumina was used as adsorbent. The main emphasis is laid on the development of a compact pulse source from a DC supply for the removal of NOX from the filtered diesel engine exhaust.

Portable HVAC and Pulsed Plasma Sources for Control of NOX in Diesel Engine Exhaust

In this paper studies were carried out on two compact electric discharge plasma sources for controlling nitrogen oxides (NOX) emission in diesel engine exhaust. The plasma sources consist of an old television flyback transformer to generate high frequency high voltage ac (HVAC) and an automobile ignition coil to generate the high voltage pulses (HV Pulse). The compact plasma sources are aimed at retrofitting the existing catalytic converters with electric discharge assisted cleaning technique. To enhance NOX removal efficiency cascaded plasma-adsorbent technique has been used. Studies were reported at different flow rates and load conditions of the diesel engine.

DeNOx Study in Diesel Engine Exhaust Using Barrier Discharge Corona Assisted by V2O5/TiO2 Catalyst

A plasma-assisted catalytic reactor was used to remove nitrogen oxides (NOx) from diesel engine exhaust operated under different load conditions. Initial studies were focused on plasma reactor (a dielectric barrier discharge reactor) treatment of diesel exhaust at various temperatures. The nitric oxide (NO) removal efficiency was lowered when high temperature exhaust was treated using plasma reactor. Also, NO removal efficiency decreased when 45% load exhaust was treated. Studies were then made with plasma reactor combined with a catalytic reactor consisting of a selective catalytic reduction (SCR) catalyst, V2O5/TiO2. Ammonia was used as a reducing agent for SCR process in a ratio of 1:1 to NOx. The studies were focused on temperatures of the SCR catalytic reactor below 200°C. The plasma-assisted catalytic reactor was operated well to remove NOx under no-load and load conditions. For an energy input of 96 J/l, the NOx removal efficiencies obtained under no-load and load conditions were 90% and 72% respectively at an exhaust temperature of 100°C.

Nonthermal-Plasma-Promoted Catalysis for the Removal of NOx From a Stationary Diesel-Engine Exhaust

A detailed study on the removal of oxides of nitrogen (NOx) from the exhaust of a stationary diesel engine was carried out using nonthermal-plasma (pulsed electrical-discharge plasma)-promoted catalytic process. In this paper, the filtered exhaust from the diesel engine is made to pass through a combination of nonthermal plasma reactor and a catalytic reactor connected in series. This combination is referred to as cascade. Two types of cascaded systems were studied. In one type, the plasma treating filtered exhaust was cascaded with a reduction catalyst V2O5/TiO2 using ammonia as reducing agent, and in the other type, the plasma treating filtered exhaust was cascaded with activated-alumina catalyst without any additive. Improved NOx-removal performance of both the cascaded processes and the role of nonthermal plasma in promoting catalysis are explained. Along with the NOx, total hydrocarbon and aldehydes were also removed. Furthermore, experiments were conducted at different temperatures and engine-loading conditions.

Treatment of NOx from Diesel Engine Exhaust by Dielectric Barrier Discharge Method

This paper reports improved performance of discharge plasma in filtered engine exhaust treatment. Our paper deals about the removal of NOX emissions from the diesel exhaust by electric discharge plasma. For the treatment of diesel exhaust a new type of reactor referred to as crossflow dielectric barrier discharge reactor has been used, where the gas flow is perpendicular to the corona electrode. Experiments were conducted at different flow rates ranging from 2 l/min to 10 l/min. The discharge plasma assisted barrier discharge reactor has shown promising results in NOX removal at high flow rates.

Application of Solar Powered High Voltage Discharge Plasma for NOX Removal in Diesel Engine Exhaust

This paper proposes a compact electric discharge plasma source for controlling NOX emission in diesel engine exhaust. Boost converter is used to boost to solar powered battery voltage to 24V, further an automobile ignition coil was used to generate the high voltage pulse using fly-back topology. This design is aimed at retrofitting the existing catalytic converters with pulse assisted cleaning technique. In this paper we bring out a relative comparison of discharge plasma and plasma-adsorbent process at different gas flow rates. Activated alumina was used as adsorbent. The main emphasis is laid on the development of a compact pulse source from 12V battery, which is powered by the solar, for the removal of NOX from the filtered diesel engine exhaust.