NO Reduction Activity Research Articles

Effect of Low Concentration of SO x on NO Reduction with Propene Over Ag/Al2O3

Catalytic activity for NO reduction with propene was investigated at 0–80 ppm SO2. NO was reduced more efficiently by propene on SO2-treated than untreated catalyst. Simultaneously, combustion of reductant was observed to lower NO reduction efficiency. Thus, the role of surface-adsorbed SOx species was regarded as depressing reductant combustion. NH3 adsorption revealed that SO2 treatment increased Bronsted acidity of the Ag/Al2O3 catalyst, which promoted propene activation. Reductant activation is a more important step, compared with NO activation to oxidative nitrate species. The NCO species, an index intermediate in NOx reduction, was produced on SO2-adsorbed Ag/Al2O3 at a lower temperature (473 K) than on the untreated catalyst. The reductive intermediates at low temperature are suggested to be alcohol, or aldehyde-adsorbed species, based on observed C=O band.

Pd-Supported Interaction-Defined Selective Redox Activities in Pd−Ce0.7Zr0.3O2−Al2O3 Model Three-Way Catalysts

Effects of Pd-supported interactions toward redox behaviors concerning three-way catalytic reactions and oxygen-buffering effects are investigated through stepwise changing Pd-loading locations over ceria−zirconia and alumina. Through light-off tests and kinetics, texture, and surface studies, discrepant but redistributable Pd−A2O3 and Pd−Ce0.7Zr0.3Ox interfaces are defined and analyzed. Pd species are inclined to promote the transformation of Ce4+ to Ce3+ and maintain themselves as fine particles on ceria−zirconia surfaces. Oxygen spillover promoted by Pdn+/Pd0−Ce4+/Ce3+ redox couples benefits the oxygen-buffering effect, but is limited by the increase of reaction temperatures and ceria−zirconia reducibility. This strong oxidative interaction overcomes the possibility of ceria-related anionic vacancies in facilitating NO dissociation and, thus, improves CO conversion only. Stochiometric light-off tests show higher activities for NO reduction and C3H8 oxidation on a Pd−Al2O3 interface, where the different morphologies and redox states of Pd-supported interfaces should be the main contributing factors for efficient molecular bond dissociation.

Effect of CaO on NH3 + NO + O2 reaction system in the absence and presence of high concentration CO2

AbstractThe effect of CaO on the NH3 + NO + O2 reaction system at 650–850 °C was investigated. High CO2 concentration was added to investigate the effect of CaCO3 on this reaction system also. Experimental results showed that CaO had a strong catalytic effect on NH3 decomposition, NH3 oxidation by O2 to NO, and NO reduction by NH3 in the absence of O2. The overall effect of CaO on the NO + NH3 + O2 reaction was to enhance NH3 oxidation by O2 to produce more NO. A small amount of NO2 and no N2O was detected in the outlet gas stream over CaO in the NH3 + NO + O2 reaction. NO2 formation decreased with temperature increase. NO2 formation in the NH3 + NO + O2 reaction over CaO was attributed to the oxidization of NH3 and NO by O2. The performance of CaCO3 was different from CaO. NH3 decomposition was promoted, but NH3 oxidation to NO was inhibited after CaO was converted to CaCO3. No catalytic activity for NO reduction was detected in NO + NH3 reaction over CaCO3, but strong activity for NH3 decomposition was observed. NO and NH3 outlet concentration over CaCO3 in the NH3 + NO + O2 reaction was lower and higher, respectively, than that of CaO, which was mainly due to the difference of CaO and CaCO3 for NH3 oxidation. NO2 formation was inhibited, but N2O was observed over CaCO3. N2O formation increased with temperature increase at 650–750 °C, and then decreased at 750–850 °C. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

High-Throughput Screening of Nanoparticle Catalysts Made by Flame Spray Pyrolysis as Hydrocarbon/NO Oxidation Catalysts

We describe here the use of liquid-feed flame spray pyrolysis (LF-FSP) to produce high surface area, nonporous, mixed-metal oxide nanopowders that were subsequently subjected to high-throughput screening to assess a set of materials for deNO(x) catalysis and hydrocarbon combustion. We were able to easily screen some 40 LF-FSP produced materials. LF-FSP produces nanopowders that very often consist of kinetic rather than thermodynamic phases. Such materials are difficult to access or are completely inaccessible via traditional catalyst preparation methods. Indeed, our studies identified a set of Ce(1-x)Zr(x)O(2) and Al(2)O(3)-Ce(1-x)Zr(x)O(2) nanopowders that offer surprisingly good activities for both NO(x) reduction and propane/propene oxidation both in high-throughput screening and in continuous flow catalytic studies. All of these catalysts offer activities comparable to traditional Pt/Al(2)O(3) catalysts but without Pt. Thus, although Pt-free, they are quite active for several extremely important emission control reactions, especially considering that these are only first generation materials. Indeed, efforts to dope the active catalysts with Pt actually led to lower catalytic activities. Thus the potential exists to completely change the materials used in emission control devices, especially for high-temperature reactions as these materials have already been exposed to 1500 degrees C; however, much research must be done before this potential is verified.

Effect of nanostructures formed by oblique co-deposition on transient catalytic reactions

We investigated the effects of nanostructures of obliquely co-sputter-deposited thin films in terms of catalytic properties using pulses of reactant molecules as probes. Pt–Al 2O 3 thin films were fabricated on a Si substrate by simultaneous oblique deposition. The films had columnar structures that grew perpendicular to the substrate. We observed the behavior of NO reduction by H 2 with a specially designed apparatus employing pulse valves for the injection of reactant molecules onto the thin film surface and a time-of-flight mass spectrometer to measure plural products. The obliquely co-deposited films, consisting of columnar nanostructures, showed higher NO reduction activity over a wide range of temperatures than the normally co-deposited films, consisting of uniform structures. The yield of N 2 exceeded that of NH 3 and N 2O for both structures in the high temperature range, whereas the yield of N 2O was more significant for the structures with columns than those without columns at low temperatures. Subtle change of the nanometer-scale structures with the deposition angle was clearly discriminated from the viewpoint of transient catalytic activity.

Effect of combination of noble metals and metal oxide supports on catalytic reduction of NO by H 2

We investigated the effects of combination of noble metals M (Rh, Pd, Ir, Pt) and metal oxide supports S (Al 2O 3, SiO 2, ZrO 2, CeO 2) on the NO + H 2 reaction using planar catalysts with M/S two layered thin films on Si substrate. In this study, NO reduction ability per metal atom were evaluated with a specially designed apparatus employing pulse valves for the injection of reactant molecules onto catalysts and a time-of-flight mass spectrometer to measure multiple transient products: NH 3, N 2 and N 2O simultaneously as well as with an atomic force microscopy to observe the surface area of metal particles. The catalytic performances of Rh and Ir catalysts were hardly affected by a choice of a metal oxide support, while Pd and Pt catalysts showed different catalytic activity and selectivity depending on the metal oxide supports. This assortment is consistent with ability to dissociate NO depending on metals without the effect of any support materials. There, the metals to the left of Rh and Ir on the periodic table favor dissociation of NO and those to the right of Pd and Pt tend to show molecular adsorption of NO. Therefore, the catalytic property of noble metals could be assorted into two groups, i.e. Rh and Ir group whose own property would mainly dominate the catalytic performance, and Pd and Pt group whose interaction with metal oxides supports would clearly contribute to the reaction of NO with H 2. NO reduction activity of Pd and Pt was found to be promoted above that of Rh and Ir, provided that Pd and Pt were supported by CeO 2 and ZrO 2.

Mercury oxidation by hydrochloric acid over TiO 2 supported metal oxide catalysts in coal combustion flue gas

Mercury oxidation by hydrochloric acid over the metal oxides supported by anatase type TiO 2 catalysts, 1 wt.% MO x/TiO 2 where M = V, Cr, Mn, Fe, Ni, Cu, and Mo, was investigated by the Hg 0 oxidation and the NO reduction measurements both in the presence and absence of NH 3. The catalysts were characterized by BET surface area measurement and Raman spectroscopy. The metal oxides added to the catalyst were observed to disperse well on the TiO 2 surface. For all catalysts studied, the Hg 0 oxidation by hydrochloric acid was confirmed to proceed. The activity of the catalysts was found to follow the trend MoO 3 ~ V 2O 5 > Cr 2O 3 > Mn 2O 3 > Fe 2O 3 > CuO > NiO. The Hg 0 oxidation activity of all catalysts was depressed considerably by adding NH 3 to the reactant stream. This suggests that the metal oxide catalysts undergo the inhibition effect by NH 3. The activity trend of the Hg 0 oxidation in the presence of NH 3 was different from that observed in its absence. A good correlation was found between the NO reduction and the Hg 0 oxidation activities in the NH 3 present condition. The catalyst having high NO reduction activity such as V 2O 5/TiO 2 showed high Hg 0 oxidation activity. The result obtained in this study suggests that the oxidation of Hg 0 proceeds through the reaction mechanism, in which HCl competes for the active catalyst sites against NH 3. NH 3 adsorption may predominate over the adsorption of HCl in the presence of NH 3.

Synthesis of Ga2O3–Al2O3 Catalysts by a Coprecipitation Method for CH4-SCR of NO

Synthesis of the γ-Ga2O3–Al2O3 solid solutions by the coprecipitation method was examined. Precipitates were obtained by adding at once an aqueous solution of aluminum and gallium nitrates to an excess base solution (reverse strike precipitation). The precipitates were calcined at 700 °C to give γ-Ga2O3–Al2O3 solid solutions. When an ammonium carbonate solution was used as the precipitant, ammonium aluminum carbonate hydroxide (ammonium dawsonite, AACH)–ammonium gallium carbonate hydroxide (AGCH) solid solutions were obtained. Calcination of the AACH–AGCH solid solutions at 700 °C gave the γ-Ga2O3–Al2O3 solid solutions which exhibited high activity for selective catalytic reduction of NO with methane.

Defect of HY as catalyst for selective catalytic reduction of NO in comparison with the pentasil zeolites

The specific behavior of HY in some steps that possibly occurred in the selective catalytic reduction of NO by hydrocarbon (HC-SCR) was investigated. Experimental results indicated that the activity of HY for NO oxidation to NO 2 was much lower than those of the pentasil zeolites (HZSM-5, HFER and HMOR). In addition, FTIR measurements showed that both nitrosonium ions (NO +) and nitrate species were remarkably produced at 300 °C over the pentasil zeolites and they were highly active towards hydrocarbons at the temperature. On the contrary, no NO + species could be detected over HY and the nitrate species produced over the zeolite were almost inactive towards reduction at the same reaction condition. It is proposed that the low amount of strong Brönsted acids of HY accounts for the above inferior founctions of the zeolite required by HC-SCR, leading to the low NO reduction activity.

Catalytic reduction of nitric oxide with carbon monoxide on copper-cobalt oxides supported on nano-titanium dioxide

A series of copper-cobalt oxides supported on nano-titanium dioxide were prepared for the reduction of nitric oxide with carbon monoxide and characterized using techniques such as XRD, BET and TPR. Catalyst CuCoOx/TiO2 with Cu/Co molar ratio of 1/2, Cu-Co total loading of 30% at the calcination temperature of 350 degrees C formed CuCo2O4 spinel and had the highest activity. NO conversion reached 98.9% at 200 degrees C. Mechanism of the reduction was also investigated, N2O was mainly yielded below 100 degrees C, while N2 was produced instead at higher temperature. O2 was supposed to accelerate the reaction between NOx and CO for its oxidation of NO to give more easily reduced NO2, but the oxidation of CO by O2 to CO2 decreased the speed of the reaction greatly. Either SO2 or H2O had no adverse impact on the activity of NO reduction; however, in the presence of both SO2 and H2O, the catalyst deactivated quickly.

Preparation of Cu/La 2O 3-ZrO 2-Al 2O 3 catalyst and its catalytic properties for selective reduction of NO

The La 2O 3-ZrO 2-Al 2O 3 composite support was prepared by co-precipitation method with the mixed aqueous solution of La(NO 3) 3, Al(NO 3) 3, and ZrOCl 2 dropping into the precipitant of (NH 4) 2CO 3 aqueous solution. The Cu/La 2O 3-ZrO 2-Al 2O 3 catalyst was prepared by the impregnation of La 2O 3-ZrO 2-Al 2O 3 with active component Cu 2+ aqueous solution. The effects of the catalyst on the selective catalytic reduction of NO with propylene in excess oxygen were investigated. The relationships among the preparation method, structure, and properties of the Cu/La 2O 3-ZrO 2-Al 2O 3 catalyst were also explored by means of Scanning electron microscope (SEM), X-ray diffraction (XRD), Surface area measurements (BET), Pyridine absorption infrared spectrum (Py-IR), thermal gravimetry (TG), and Temperature-programmed reduction (TPR). The results indicate that the support J-Al 2O 3 prepared by Al(NO 3) 3 dropping into (NH 4) 2CO 3 can remarkably enlarge the surface area; the addition of La 2O 3 contributes mainly to the enhancement of the thermal stability; and the introduction of ZrO 2 can increase the amount of Lewis and BrInsterd acid. Consequently, the catalyst Cu/La 2O 3-ZrO 2-Al 2O 3 has excellent activity for the selective reduction of NO with propylene in excess oxygen. The NO conversion is up to 88.9% at 300°C and 81.9% even at the presence of 10% volume fraction of water vapor.

Examining the surface of a synergistic Pt-Rh/γ-Al2O3 catalyst using NO as a probe molecule

The interaction of NO and NO+H2 with reduced γ-Al2O3, Pt/γ-Al2O3, Rh/γ-Al2O3, Pt(90%)-Rh/(10%)/γ-Al2O3 (90/10), and Pt(95%)-Rh(5%)/γ-Al2O3 (95/5) was monitored with FTIR spectroscopy to better understand the surface of a synergistic Pt-Rh catalyst (95/5). The surface of the alloy nanoparticles on the synergistic 95/5 catalyst contained both Pt and Rh due to the presence of FTIR peaks representing linear NO on Pt and NO on Rh. The presence of Pt and Rh on the surface of 90/10 was confirmed through the observation of the linear NO-on-Pt peak and the Rh nitrosyl peak, respectively. The presence of the Rh nitrosyl peak at 150°C and 200°C on 90/10 indicates the presence of partially oxidized Rh on the surface of the supported Pt-Rh alloy particles at these temperatures. The following relative order of NO reduction activity was observed for the prepared catalysts: 95/5>Pt/γ-Al2O3≈90/10≫Rh/γ-Al2O3. The maximum synergistic performance of 95/5 was a five-fold increase over the activity of Pt/γ-Al2O3, and this was only observed after conditioning the catalyst by equilibrating to reaction conditions for 10h at 250°C. A discussion of the reaction mechanism and the observed surface species reveals that the differing performance of 95/5 and 90/10 is related to the amount of Rh on the surface of the supported alloy nanoparticles.

Synthesis and characterization of Sm 3+-doped Y(OH) 3 and Y 2O 3 nanowires and their NO reduction activity

A highly crystallized hexagonal structure with large aspect-ratios, almost uniform diameter and length of several tens of microns of Y(OH) 3 nanowires, have been successfully synthesized by controlling the hydrothermal reaction time as well as an addition of 5 mol% Sm 3+ at 180 °C for 24 h under N 2 atmosphere. The hydrothermal products of yttrium nitrate precursor alone have showed merely nanosheets like structure under the same reaction conditions. The microstructures of the Y(OH) 3 nanowires were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution (HR)TEM and selected area electron diffraction (SAED). After heat treatment, the as-prepared Y(OH) 3 could be completely transformed into Y 2O 3 while maintaining the nanowires structure up to the temperature at 400 °C in air. The Y 2O 3:Sm 3+ have been tested for the reduction of NO under an oxidizing atmosphere with hydrocarbons. Moreover, the NO reduction activity under atmosphere containing water vapor was also investigated.

A functional nitric oxide reductase model

A functional heme/nonheme nitric oxide reductase (NOR) model is presented. The fully reduced diiron compound reacts with two equivalents of NO leading to the formation of one equivalent of N(2)O and the bis-ferric product. NO binds to both heme Fe and nonheme Fe complexes forming individual ferrous nitrosyl species. The mixed-valence species with an oxidized heme and a reduced nonheme Fe(B) does not show NO reduction activity. These results are consistent with a so-called "trans" mechanism for the reduction of NO by bacterial NOR.

Preparation of apatite-type-silicate-supported precious metal catalysts for selective catalytic reduction of NOx

Apatite-type silicate supported precious metal catalysts were prepared and investigated for their catalytic activity in selective catalytic NO reduction. Single-phase La9.33Si6O26 and La8.33ASi6O25.5 (A=Ca, Sr, Ba) were obtained by a sol-gel method. Pd/La9.33Si6O26 catalyst exhibited high activity for oxidation of C3H6, comparable to Pd/Al2O3 catalyst, although the specific surface area of La9.33Si6O26 was lower than that of Al2O3. In addition, Pt/La9.33Si6O26 catalyst exhibited higher activity for selective catalytic reduction of NO than Pt/Al2O3 catalyst. Substitution of Ba2+ for La3+ of La9.33Si6O26 led to increased catalytic activity at low temperature.

Low-temperature Catalytic Reduction of Nitrogen Monoxide with Carbon Monoxide on Copper Iron and Copper Cobalt Composite Oxides

Copper iron composite oxides (CuO/Fe2O3) and copper cobalt composite oxides (CuO/Co3O4) for the catalytic reduction of NO with CO at low temperature were prepared by co-precipitation. The catalytic activity and thermal stability of the catalysts were evaluated by a microreactor-GC system. The 100% conversion temperatures of NO are 80C for CuO/Fe2O3 and 90C for CuO/Co3O4. The catalysts possess high catalytic activity and favorable thermal stability for NO reduction with CO in a wide temperature range and long time range. A systematic study of the molar ratios of the reactants, the volume of NaOH, aging time, and calcination temperature/time was carried out to investigate the influence preparation conditions on the catalytic activity of the catalysts.

SO2 poisoning of LaFe0.8Cu0.2O3 perovskite prepared by reactive grinding during NO reduction by C3H6

Nanoscale LaFe0.8Cu0.2O3 was prepared by reactive grinding, characterized by XRD, SEM, H2-TPR, O2-, NO + O2-, and C3H6-TPD (with and without SO2), FTIR, tested for catalytic reduction of NO by C3H6 and aged in presence of SO2 to investigate the effect of sulfurous species on its catalytic behavior. Two distinct poisoning mechanisms depending on SO2 feed concentration were thus proposed. At low concentration SO2 (≤20 ppm) can cause a reversible poisoning due to the competitive adsorption of SO2 and reactants as well as the coverage of active sites by surface sulfite and sulfate species. By contrast, 80 ppm SO2 leads to a severe sulfatation with destruction of the perovskite structure and the generation of La2(SO4)3 and Fe2O3 phases resulting in an irreversible loss of activity in NO reduction by C3H6. Partial regeneration of this spent sample can be realized by releasing sulfur from the perovskite under a 5% H2/He atmosphere followed by reconstructing the perovskite structure under an oxygen containing atmosphere.

Electrochemical reduction of NO and O2 on La2−x Sr x CuO4-based electrodes

A series of La2 − x Sr x CuO4 (x = 0.0, 0.05, 0.15, 0.25 and 0.35) compounds was investigated for the use of direct electrochemical reduction of NO in an all-solid-state electrochemical cell. The materials were investigated using cyclic voltammetry in 1% NO in Ar and 10% O2 in Ar. The most selective electrode material was La2CuO4, which had an activity of NO reduction that was 6.8 times higher than that of O2 at 400 °C. With increasing temperature, activity increased while selectivity decreased. Additionally, conductivity measurements were carried out, and the materials show metallic conductivity behavior which follows an adiabatic small polaron hopping mechanism.

Spectroscopic and catalytic characterization of Co-exchanged mordenites subject to CO/O 2 redox treatments

Co-mordenites were prepared by ion exchange and wet impregnation over Na-mordenite and H-mordenite. The prepared solids were calcined and aliquots of these samples were subject to redox treatments first with CO for 2 h at 773 K and then kept 2 h at the same temperature in flowing O 2. A thorough characterization of the solids was carried out by TPR, XPS, CO volumetric adsorption, and FTIR with CO, NO and pyridine adsorption as probe molecules. After the redox treatment, Na based samples showed an important increase in the CO adsorption. TPR and XPS results indicated reduction of the oxides present in the calcined samples and the migration of exchanged cobalt from hidden to more exposed sites was demonstrated by FTIR. The acid catalysts did not change their CO capacity of adsorption; exchanged cobalt ions were mainly in β-type sites and remained in this position after treatment. After the redox treatments, the activity for the selective reduction of NO x with methane suffered a decrease on both types of mordenites, probably caused by the strong adsorption of NO and the reduction of β-type Co 2+ to metallic cobalt that would diminish the active sites concentration and also block the channels, thus preventing the access of the reactants.

Reaction of NO over Iridium Catalysts with Excess Oxygen

A series of iridium-supported catalysts with various Ir loadings were prepared by impregnation method. The support materials used were ZSM-5, γ-Al2O3, and SiO2. The Ir loadings examined were 0.02%, 0.1%, 1%, and 5% (w). The behavior of the catalysts for the NO reaction was analyzed by means of temperature programmed reaction (TPR) experiments. The reactions of NO over iridium include the oxidation of NO to NO2 and the reduction of NO to N2 or N2O. The iridium catalysts promote the reactions of NO and the catalytic activity increases with the increase of the Ir loadings. Further, support materials have a little effect on the catalytic activity. When the loading was less than 0.1%, the catalytic activity was found to be dependent on the property of support materials and the activity order was Ir/ZSM-5Ir/γ-Al2O3Ir/SiO2; when the loading was higher than 0.1%, the order of catalytic activity for NO oxidation was Ir/ZSM-5Ir/SiO2Ir/γ-Al2O3, which was correlated with Ir dispersion on the surface of support materials, and the order of catalytic activity for NO reduction was Ir/γ-Al2O3Ir/SiO2Ir/ZSM-5, which was attributed to the adsorbed-dissociation of NO2. Ir/γ-Al2O3 catalyst was more beneficial for the NO reduction than Pt/γ-Al2O3 catalyst.