Performance For NO Reduction Research Articles

Enhanced Low Temperature NO Reduction Performance via MnOx-Fe2O3/Vermiculite Monolithic Honeycomb Catalysts

Selective catalytic reduction of NOx by ammonia (NH3-SCR) was the most efficient and economic technology for De-NOx applications. Therefore, a series of MnOx/vermiculite (VMT) and MnOx-Fe2O3/VMT catalysts were prepared by an impregnation method for the selective catalytic reduction (SCR) of nitrogen oxides (NOx). The MnOx-Fe2O3/VMT catalysts provided an excellent NO conversion of 96.5% at 200 °C with a gas hourly space velocity (GHSV) of 30,000 h−1 and an NO concentration of 500 ppm. X-ray photoelectron spectroscopy results indicated that the Mn and Fe oxides of the MnOx-Fe2O3/VMT catalyst were mainly composed of MnO2 and Fe2O3. However, the MnO2 and Fe2O3 components were well dispersed because no discernible MnO2 and Fe2O3 phases were observed in X-ray powder diffraction spectra. Corresponding MnOx-Fe2O3/VMT monolithic honeycomb catalysts (MHCs) were prepared by an extrusion method, and the MHCs achieved excellent SCR activity at low temperature, with an NO conversion greater than 98.6% at 150 °C and a GHSV of 4000 h−1. In particular, the MnOx-Fe2O3/VMT MHCs provided a good SCR activity at room temperature (20 °C), with an NO conversion of 62.2% (GHSV = 1000 h−1). In addition, the NO reduction performance of the MnOx-Fe2O3/VMT MHCs also demonstrated an excellent SO2 resistance.

Performance of NO Reduction by Reburning Assisted by Iron Wire

NO could be reduced by CH4, CO and H2 in the reburning process. In this paper, the reduction of NO by CH4, CO and H2 was investigated when assisted by iron wire and its oxides. In a temperature range of 600-800℃, it was observed that iron had little catalytic effect for the reduction of NOx by CH4 and H2, but CO presented better reduction performance by the catalytic assistance of iron. In the absence of O2, iron shows a weak catalytic effect for the reduction of NOx by CO at 600-700℃ and a strong catalytic effect at 800℃. O2 gave a great inhibition for NOx reduction by CO over iron. The following catalytic activity order of iron and its oxides was observed: FexOy<Fe<Fe (after oxidation/reduction pretreatment).

Effect of Mg/Al molar ratios on NO reduction activity of CO using Ce-La/MgAl2O4-x catalysts

A series of Ce-La/MgAl2O4-x catalysts were prepared by the incipient wetness impregnation method and characterized by BET, XRD, H2-TPR, CO-TPR and in situ FT-IR. The results demonstrate that the catalyst with a Mg/Al molar ratio of 0.5 yields the most uniform dispersion of CeO2 and greatly enhances formation of Ce-O-La solid solution, resulting in the increase of oxygen vacancy and surface Ce3+ content. Thereby, the synergistic effect between surface Ce3+ and oxygen vacancy gives rise to the best catalytic performance of NO reduction. Moreover, introduction of Mg species suppresses tranformation of CeO2 to Ce(SO4)2/Ce2(SO4)3 and then improves the SO2 resistance performance of Ce-La/MgAl2O4−0.5.

Selective catalytic reduction of NOx with NH3 over iron-cerium-tungsten mixed oxide catalyst prepared by different methods

A series of magnetic Fe0.85Ce0.10W0.05Oz catalysts were synthesized by three different methods(Co-precipitation(Fe0.85Ce0.10W0.05Oz-CP), Hydrothermal treatment assistant critic acid sol-gel method(Fe0.85Ce0.10W0.05Oz-HT) and Microwave irradiation assistant critic acid sol-gel method(Fe0.85Ce0.10W0.05Oz-MW)), and the catalytic activity was evaluated for selective catalytic reduction of NO with NH3. The catalyst was characterized by XRD, N2 adsorption-desorption, XPS, H2-TPR and NH3-TPD. Among the tested catalysts, Fe0.85Ce0.10W0.05Oz-MW shows the highest NOx conversion over per gram in unit time with NOx conversion of 60.8% at 350°C under a high gas hourly space velocity of 1,200,000ml/(gh). Different from Fe0.85Ce0.10W0.05Oz-CP catalyst, there exists a large of iron oxide crystallite(γ-Fe2O3 and α-Fe2O3) scattered in Fe0.85Ce0.10W0.05Oz catalysts prepared through hydrothermal treatment or microwave irradiation assistant critic acid sol-gel method, and higher iron atomic concentration on their surface. And Fe0.85Ce0.10W0.05Oz-MW shows higher surface absorbed oxygen concentration and better dispersion compared with Fe0.85Ce0.10W0.05Oz-HT catalyst. These features were favorable for the high catalytic performance of NO reduction with NH3 over Fe0.85Ce0.10W0.05Oz-MW catalyst.

Understanding the effect of CuO dispersion state on the activity of CuO modified Ce0.7Zr0.3O2 for NO removal

In this work, CuO modified Ce0.7Zr0.3O2 (CZ) solid solution including CuO-deposited CZ (i.e., Cu/CZ) and −doped CZ (i.e., Cu-CZ) are prepared. The correlation of CuO neighboring structure with the catalytic performance for NO reduction have been proposed by various spectroscopic technologies. Results suggested that the strong synergetic effect between surface deposited copper species and CZ support can easily promote the reducibility of Cu/CZ, which enhances its catalytic performance. In addition, the decomposition of NO occurs through different pathways over Cu/CZ and Cu-CZ, respectively, as suggested by in-situ FTIR results. The distinct chemical state and environment of copper species between Cu/CZ and Cu-CZ can account for these differences. A surface model and the reaction mechanism are proposed to discuss the differences showing in the catalysts.

Catalytic Performance of NO Reduction by CO over Activated Semicoke Supported Fe/Co Catalysts

Performance of NO reduction by CO is studied over activated semicoke supported Fe/Co catalysts (FeCo/ASC). The influence of oxygen and CO concentration is investigated systematically. It is found that excess CO, with a CO:NO ratio greater than 2:1, could significantly enhance NO reduction, but oxygen, even with a concentration less than 1%, could strongly inhibit NO conversion efficiency due to the oxidation of active surface metal sites. To explore the role of CO in NO reduction, reactions without CO addition are also conducted. By comparing NO reduction behavior in the presence and absence of CO, it is found that carbon support is the main reducing agent if oxygen is in great excess, even when CO is provided. At the same time, NO reduction efficiency increases at higher oxygen concentration due to the increase of surface oxygen complex. However, excess oxygen is strongly undesired because serious gasification of carbon support is inevitable. But if oxygen concentration is not very high, CO could be fed ...

The formation of CuO/OMS-2 nanocomposite leads to a significant improvement in catalytic performance for NO reduction by CO

CuO/OMS-2 nanocomposites with different Cu/Mn molar ratios of 0.148, 0.332, 0.569, and 0.886 were prepared by loading cupric oxide on OMS-2 nanorods. The formation of the CuO/OMS-2 nanocomposites significantly increases NO conversion and N2 yield for the reduction of NO by CO. The CuO/OMS-2 nanocomposite with the optimum Cu/Mn molar ratio of 0.569 (CuO/OMS-2-C) exhibited excellent catalytic activity at lower temperature below 300°C, which is much better than a commercial precious metal catalyst (0.84wt% Pd/MgO-Al2O3-SiO2). Compared to the commercial precious metal catalyst, T50 and T90 (the reaction temperature corresponding to 50% and 90% of NO conversion) of CuO/OMS-2-C are significantly reduced by ΔT50=126°C, ΔT90=100°C, respectively. Even at the low temperature of 240°C, the N2 yield of CuO/OMS-2-C is as high as 93.8%. In striking contrast, the N2 yield of the pure OMS-2 nanorod sample and the commercial precious metal catalyst is as low as 3.6%, 8.0% at 240°C, respectively. CuO/OMS-2-C exhibited excellent durability for the reduction of NO by CO. Even after operated at 300°C for 140h, the catalytic activity almost remained unchanged. The evolution of the catalytic active phases or sites for CuO/OMS-2-C with the elevation of the reaction temperature was investigated by CO temperature-programmed reduction, TEM, XRD, and XPS. When the temperature increases above 240°C, the catalytic active phases of the CuO/OMS-2 nanocomposites are reconstructed to metallic Cu and Mn3O4. These characterizations reveal that the formation of the CuO/OMS-2-C nanocomposite considerably promotes the reduction of OMS-2 to catalytic active phase of Mn3O4 as well as the reduction of CuO to catalytic active phase of metallic Cu. The more active catalytic sites of Mn3+ ions and metallic Cu in the CuO/OMS-2-C nanocomposite produced at lower temperature together with the synergetic effect between Mn3O4 and metallic Cu significantly improve the NO conversion and N2 yield as compared to pure OMS-2 and nano CuO.

Synthesis of Copper-Based Nanostructured Catalysts on SiO2-Al2O3, SiO2-TiO2, and SiO2-ZrO2 Supports for NO Reduction.

The selective catalytic reduction of NO over a series of Cu-based catalysts supported on modified silica including SiO2-Al2O3, SiO2-TiO2, and SiO2-ZrO2 prepared via a sol-gel process and a flame spray pyrolysis (FSP) was studied. The prepared catalysts were characterized by means of TEM, XRD, XRF, TPR, and nitrogen physisorption measurement techniques, to determine particle diameter, morphology, crystallinity, phase composition, copper reducibility, surface area, and pore size of catalysts. The particles obtained from sol-gel method were almost spherical while the particles obtained from the FSP were clearly spherical and non-porous nanosized particles. The effects of Si:Al, Si:Ti, and Si:Zr molar ratio of precursor were identified as the domain for different crystalline phase of materials. It was clearly seen that a high SiO2 content inhibited the crystallization of materials. The BET surface area of catalysts obtained from sol-gel method was higher than that from the FSP and it shows that surface area increased with increasing SiO2 molar ratio due to high surface area from SiO2. The catalyst performances were tested for the selective catalytic reduction of NO with H2. It was found that the catalyst prepared over 7 wt% Cu on Si02-Al2O3 support was the most active compared with the others which converted NO as more than 70%. Moreover, the excess copper decreased the performance of NO reduction, due to the formation of CuO agglomeration covered on the porous silica as well as the alumina surface, preventing the direct contact of CO2 and AL2O3.

The effects of Na/K additives and flyash on NO reduction in a SNCR process

An experimental study of Na/K additives and flyash on NO reduction during the selective non-catalytic reduction (SNCR) process were carried out in an entrained flow reactor (EFR). The effects of reaction temperature (Tr), water vapor, Na/K additives (NaCl, KCl, Na2CO3) and flyash characteristics on NO reduction were analyzed. The results indicated that NO removal efficiency shows a pattern of increasing first and decreasing later with the increase of the temperature at Tr=850–1150°C. Water vapor can improve the performance of NO reduction, and the NO reduction of 70.5% was obtained while the flue gas containing 4% water vapor at 950°C. Na/K additives have a significant promoting effect on NO reduction and widen the SNCR temperature window, the promoting effect of the test additives is ordered as Na2CO3>KCl>NaCl. NO removal efficiency with 125ppm Na2CO3 and 4% water vapor can reach up to 84.9% at the optimal reaction temperature. The additive concentration has no significant effects on NO reduction while its concentration is above 50ppm. Addition of circulating fluidized combustion (CFB) flyash deteriorates NO reduction significantly. However, CFB flyash and Na/K additives will get a coupling effect on NO reduction during the SNCR process, and the best NO reduction can reach 72.3% while feeding Na2CO3-impregnated CFB flyash at 125ppm Na2CO3 and Tr=950°C.

Correlation between the physicochemical properties and catalytic performances of CexSn1–xO2 mixed oxides for NO reduction by CO

A series of CexSn1–xO2 mixed oxides and single oxides (CeO2 and SnO2) were prepared by inverse co-precipitation method and calcined at 450 and 750°C to investigate the correlation between the physicochemical properties and catalytic performances of these catalysts for NO reduction by CO. The obtained samples were characterized in detail by means of XRD, UV-Raman, N2-physisorption, H2-TPR, XPS, and in situ DRIFTS technologies. Moreover, the catalytic performances of these samples were evaluated through NO reduction by CO model reaction. These results indicate that the incorporation of Sn4+ into the lattice of CeO2 can result in the decrease of crystallite size, the increase of lattice strain and the improvement of reduction behavior, which are beneficial to the enhancement of catalytic performance. Furthermore, the catalyst with the optimal mole ratio (Ce:Sn=2:1) exhibits the best catalytic performance for NO reduction by CO model reaction, because that more catalytic domains (CD, -Ce3+-□-Sn2+- species) can be generated in the reaction process due to the enhancement of reduction behavior and the formation of uniform solid solution without crystalline SnO2 blocking the active sites. Finally, in order to explore the significant role of catalytic domain (CD, -Ce3+-□-Sn2+- species) in NO reduction by CO model reaction, a possible reaction mechanism is tentatively proposed.

Preparation of high-aspect-ratio TiO2 nanotube arrays for the photocatalytic reduction of NO in air streams

The aim of this study is to fabricate TiO2 nanotubes arrays (TNTs) with smooth homogenous morphology by the anodization of titanium foil in fluorine-contained electrolytes. A series of materials analysis techniques, such as field-emission scanning electron microscopy, potentiostat/galvanostat and X-ray diffractometer, are used to characterize the surface morphology, phase formation, lattice parameters and the induced photocurrent intensity of TNTs. As the experimental results, the tube dimension of TNTs is found to be determined by the migration and diffusion of ions in the electrolyte corresponding to the concentration profiles of oxygen-containing anionic species and hydrogen ions within the TiO2 nanotubes. High-aspect-ratio TNTs with a superior degree of regularity and homogeneity are favored to be formed in the fluoride-contained ethylene glycol solutions due to the suppression of pH bursts and local ions concentration fluctuations during anodization in the highly viscous electrolytes. To compare the NO reduction by photo-SCR using spherical TiO2 (P25) and tubular TiO2, the performance of NO reduction by photo-SCR is significantly affected by the available surface area (active sites) of TiO2 rather than the crystal composition of TiO2.

The effect of CO on NO reduction over Pt/Pd-based NSR catalysts at low temperature

The present work investigates the effect of CO on NO reduction during the rich period over Pt/Pd-based NSR catalysts at low temperature. Three types of reducing agents (CO and/or H2) are used in this research. BET and XRD are used to determine physical properties, and in situ DRIFTS explore the competitive adsorption of NO–CO and the strength of CO adsorption on the noble metal component. It is found that NO is completely reduced over Pt/Pd-based catalysts at 150 °C when H2 is the reducing agent, while there is NO emission phenomenon when CO is the reducing agent. When H2 and CO are reductants together, catalysts with/without Pd exhibit different NO reduction activity. In situ DRIFTS results show that there is a competitive adsorption of NO and CO on Pt/Al2O3 and Pd/Al2O3, and Pt/Al2O3 presents stronger CO adsorption in comparison with Pd/Al2O3. It is probable that the NO reduction is related to CO adsorption on the noble metal component. The adsorption strength of CO on Pt/Pd-based catalysts affects the NO reduction performance during the rich period.

Development of gas diffusion electrodes for cogeneration of chemicals and electricity

This study reports the development and evaluation of gas diffusion electrodes (GDEs) for application in a fuel cell reactor aimed at the production of hydroxylamine. Electrode materials manufactured by two different methods are reported. The composition of the active layer of these electrodes has been tailored for application as gas diffusion cathodes for a NO-H2 fuel cell. The results on physico-chemical characterization of the catalyst layers (density, water porosity, total porosity and BET surface area) are discussed in relation with the differences in their composition (carbonaceous powder and binder used, ratios carbon to binder). The gas porous electrodes were first tested in an electrochemical half cell configuration (3-electrode configuration) for their ability to reduce diluted nitric oxide (6% in nitrogen). Later, the performance in a NO-H2 fuel cell was evaluated for the promising electrodes in a single cell set-up (2-electrode configuration). It was observed that non-platinized electrodes offer an acceptable performance for NO reduction. In the single cell set-up, current densities of −12mAcm−2 for a non-platinized electrode and −10mAcm−2 for a non-catalyzed activated charcoal electrode were obtained at 50mV cell voltage, vs. 17mAcm−2 for a platinized charcoal electrode.

Development of Iridium Catalysts for Selective Reduction of NO with CO

The development of Ir/SiO2-based catalysts for the selective reduction of NO with CO in the presence of O2 is described in this review paper. The catalytic activity of Ir/SiO2 was promoted considerably by addition of Nb2O5 and WO3. These promoted catalysts showed NO reduction activity even in the absence of SO2, in contrast to Ir/SiO2 catalyst. The addition of Nb2O5 was found to stabilize Ir metal as the active species for NO reduction. Also in the case of WO3, it was concluded that Ir metal interacting strongly with WO3 (denoted as Ir–WO3) is the catalytic active species. High temperature calcination created preferentially the Ir–WO3 species. The catalytic activity and durability of Ir/WO3/SiO2 was further promoted by addition of Ba. The developed Ba/Ir/WO3/SiO2 catalyst in monolithic form showed good performance for NO reduction for actual diesel exhaust.

Study on NO Reduction and Its Heterogeneous Mechanism through Biomass Reburning in an Entrained Flow Reactor

The effects of biomass types (including cotton stalk, wheat straw, rice husk, and rice straw), the stoichiometric ratio in the reburning-zone (SR2), the reaction temperature in the reburning-zone (t2), the particle sizes of biomass reburning fuels (dp), and the reburning fuel fraction (Rff) on NO reduction efficiency during biomass reburning were investigated systematically in an entrained flow reactor. The NO heterogeneous reduction mechanism resulting from the reburning of wheat straw and its char was analyzed. The results indicated that cotton stalk has the best performance of NO reduction, wheat straw is in second place, and rice husk and rice straw are less effective. In the range of t2 = 900–1100 °C NO reduction efficiency increases when the reburning-zone reaction temperature is increased at the same SR2. NO reduction efficiency increases insignificantly with a decrease in the particle size of the biomass with dp < 425 μm. NO reduction efficiency follows a pattern of first increasing and then decre...

Photocatalytic NO reduction with C 3H 8 using a monolith photoreactor

Photocatalytic reduction of nitric oxide was studied on a PtO x PdO y /TiO 2-coated monolith photoreactor using propane as the reducing agent. The performance of NO reduction was compared under three reaction conditions including NO/propane, NO/propane/O 2 and NO/propane/H 2O at three reaction temperatures, 25, 70 and 120 °C. The NO/propane system showed the best performance of near 90% conversion at 25 °C. The NO conversion decreased slightly as temperature increased in NO/propane system, however, NO/propane/O 2 and NO/propane/H 2O systems showed an opposite trend. Oxygen and water significantly inhibited the reduction of NO because oxygen competed with NO as oxidant, and water interfered the adsorption of both NO and propane. TiO 2 became super-hydrophilic under UV-light irradiation thus the catalyst surface was easily covered by water in moisture condition. By increasing the reaction temperature, water tended to desorb from the catalyst surface thus released more active sites for NO photoreduction. An in situ FTIR was also performed to study the intermediate species of the NO/propane and NO/propane/O 2 systems under UV-light irradiation. The results indicated that NO went through both oxidation and reduction with C 3H 8 on PtO x PdO y /TiO 2. The reaction path of NO might change with increasing temperature.

Promotional Effect of Gadolinia on CuO Catalyst for Reduction of NO by Activated Carbon

The Gd2O3 (gadolinia) modified CuO/AC catalysts for NO reduction by activated carbon were prepared and characterized by XRD, TPD-MS, EPR, XPS techniques. The results show that adding a small amount of Gd2O3 in the CuO catalyst can improve effectively its catalytic performance for NO reduction by activated carbon, and the appropriate molar ratio of Gd2O3/CuO is 0.03:1. The promotional effect of Gd2O3 stems from the cooperative effects between CuO and Gd2O3. The presence of Gd2O3 in the catalyst can alter the chemical state and environment of the CuO active sites and improve the catalytic activation of carbon by CuO to form more carbon reactive sites, resulting in the quicker transfer and release of oxygen decomposed from NO. The carboxylic groups on the surface of activated carbon play an important role in the catalytic reduction of NO by carbon at temperature below 300 °C.

Fitting of kinetic parameters of NO reduction by CO in fibrous media using a genetic algorithm

An empirical model is fitted to the performance of NO reduction by CO gas on an alumina fibrous catalyst support media. The model is highly non-linear and contains 13 fitted parameters. To fit the reaction kinetic parameters in the model to the experimental results, a genetic algorithm was applied to search for the best fit parameter values. The fitted model and experimental results for Pd, Pt and Rh catalysts are in good agreement. The effects of NO decomposition by varying fiber diameter, media depth, and catalyst particle size on rhodium catalyst can be calculated from the model. The model results show the temperature of complete NO decomposition decreases with greater media depth, higher fractional area of coverage by the catalyst particles, and with smaller catalyst particle size.

Hydrothermal synthesis of Sr–Ce–Sn–Mn–O mixed oxidic/stannate pyrochlore and its catalytic performance for NO reduction

Mixed oxides and pyrochlore-type materials based on the Sr, Ce, Sn, and Mn elements have been prepared by hydrothermal method using a mixture of nitrate salts at 200 °C for 40 h under N 2 atmosphere. Two groups of solids were synthesized: (i) (Sr x Ce 1− x ) 2Sn 2O 7± δ (0.345 ≤ x ≤ 0.365) and (ii) (Sr x Ce 1− x ) 2(Sn y Mn 1− y ) 2O 7± δ (0.345 ≤ x ≤ 0.365, 0.385 ≤ y ≤ 0.395). The structure of the solids were studied by X-ray diffraction and the main crystal phases determined were SnO 2, (SrCe) 2Sn 2O 7 and a trace amount of CeO 2 in group (i) and only SnO 2 and CeO 2 were detected in group (ii). The mixed oxides/stannate pyrochlore have been tested as catalyst for NO reduction with hydrocarbons (CH 4, C 2H 4, and C 3H 6) in the presence of O 2. The CeO 2 containing stannate Sr 2 x Ce 2−2 x Sn 2O 7± δ pyrochlore coexist with SnO 2 (group (i)) was found to be the best for NO + C 3H 6 reaction giving very high N 2 production at 350 °C in the presence of O 2 and water vapor. SnO 2 as well as CeO 2 alone were also synthesized by the hydrothermal method and their NO reduction properties have been compared with those of the groups (i) and (ii).

NO reduction performance of Rh paste catalyst on YSZ under steady state and forced oscillation electropromotion conditions

The technique of cyclic voltammetry was applied in conjunction with on-line catalytic product analysis to investigate the electrochemical promotion of NO reduction by C3H6 in presence of O2 on Rh catalyst-electrode films on YSZ at temperatures 350–490 °C. Cyclic linear potential sweep amperometry under catalytic reaction conditions leads to cyclic non-Faradaic electrochemical modifications in the CO2 formation and NO reduction rates which are compared to those obtained under steady state potentiostatic operation.