NO Reduction Activity Research Articles

Performance of Ba-doped Ir/WO<sub>3</sub>-SiO<sub>2</sub> Catalyst for Selective Catalytic Reduction of NO<sub><i>x</i></sub> with CO in Diesel Exhaust

Ba-doped Ir/WO3-SiO2 catalyst has high activity and good durability for the selective catalytic reduction of NO with CO in the presence of O2 (CO-SCR). The performance of this catalyst was investigated for real diesel exhaust. In addition, the possibility of a combined catalytic system using CO-SCR and NH3-SCR was evaluated. Ba/Ir/WO3-SiO2 catalyst provided more than 45% conversion with 3000 ppm CO at 280°C under SV (space velocity) <6000 h−1, even with high oxygen concentrations. The activity of a combined catalyst system using Cu-BEA for NH3-SCR and Ba/Ir/WO3-SiO2 for CO-SCR was evaluated. The combined catalyst provided about 60% NOx conversion when only NH3 was added. NOx conversion was further increased with the addition of 3000 ppm CO. Thus, the efficiency of the combined system was confirmed. Improvement of activity under high space velocity and prevention of catalyst deactivation by smoke are the key targets for the development of practical systems.

Catalytic reduction of NO by CO over NiO/CeO2 catalyst in stoichiometric NO/CO and NO/CO/O2 reaction

A new catalyst composed of nickel oxide and cerium oxide was studied with respect to its activity for NO reduction by CO under stoichiometric conditions in the absence as well as the presence of oxygen. Activity measurements of the NO/CO reaction were also conducted over NiO/γ-Al2O3, NiO/TiO2, and NiO/CeO2 catalysts for comparison purposes. The results showed that the conversion of NO and CO are dependent on the nature of supports, and the catalysts decreased in activity in the order of NiO/CeO2>NiO/γ-Al2O3>NiO/TiO2. Three kinds of CeO2 were prepared and used as support for NiO. They are the CeO2 prepared by (i) homogeneous precipitation (HP), (ii) precipitation (PC), and (iii) direct decomposition (DP) method. We found that the NiO/CeO2(HP) catalyst was the most active, and complete conversion of NO and CO occurred at 210°C at a space velocity of 120,000h−1. Based on the results of surface analysis, a reaction model for NO/CO interaction over NiO/CeO2 has been proposed: (i) CO reduces surface oxygen to create vacant sites; (ii) on the vacant sites, NO dissociates to produce N2; and (iii) the oxygen originated from NO dissociation is removed by CO.

Effects of sodium modification, different reductants and SO 2 on NO reduction by Rh/Al 2O 3 catalysts at excess O 2 conditions

Although many catalysts of NO reduction have been developed, the presence of excess O 2 and SO 2 significantly inhibits their performance when they are used to treat the incineration flue gas. To solve such problem, this study prepared new Rh/Al 2O 3 catalysts and investigated the effects of Na modification, SO 2 and different reductants. Experimental results indicated that the average removal efficiency of NO at such high O 2 concentrations exceeded 80% when the Rh/Al 2O 3 catalysts were used. CO was a better reductant than C 3H 6 and the best concentration ratio of reductant/NO was equal to 1. Adding Na to modify Rh/Al 2O 3 catalysts significantly enhanced the removal efficiency of NO from 80 to 99% at 250–300 °C, especially at relative high SO 2 concentrations. Unfortunately, Rh–Na/Al 2O 3 catalysts do not have long-time activities for NO reduction, possibly because of the formation of NaNO 3. Both Rh/Al 2O 3 and Rh–Na/Al 2O 3 catalysts have good performance for NO reduction, they can feasibly be used to reduce NO in the flue gas from waste incineration.

Catalityc removal of nitrogen oxide from combustion gases

Catalityc removal of nitrogen oxide from combustion gases Nitrogen oxide conversion to nitrogen over Pt/Al2 O3, Pd/Al2O3, Rh/Al2O3 catalysts was investigated. The results of the catalytic activity investigations, with the iso-x method, showed that NO reduction by methane occurs at a reasonable rate at the temperature range 200-500°C. Alumina-supported Pd, Pt and Rh catalysts have been compared for the selective reduction of NO to N2. All the catalysts showed good activity in NO reduction by methane, giving around 80 - 90% N2 production. At moderate temperatures Pt is the most active catalyst for the removal of NO.

Kinetics and mechanism of NO reduction with CO on Ir surfaces

The adsorption and thermal reactivity of NO and CO and the kinetics of the NO reduction with CO on Ir surfaces were studied using X-ray photoelectron spectroscopy, polarization modulation infrared reflection–absorption spectroscopy, and temperature programmed desorption. The NO adsorption and dissociation activity was strongly dependent on the Ir surface structure. The NO dissociation activity of the Ir planes decreased in the order (100) > (211) ≫ (111). In contrast, the type of the CO adsorption site was independent of the Ir surface structure. The activity of Ir(111) for N 2 and CO 2 production from the NO + CO reaction was low compared with the activities of Ir(100) and Ir(211). The kinetic data for an Ir/SiO 2 powder catalyst were similar to data obtained for Ir(211). The order of the turnover frequencies for N 2 and CO 2 formation for the Ir planes was in good agreement with the order for NO dissociation activity, and this agreement indicates that the catalytic activity for NO reduction was dependent on NO dissociation. A kinetic study of the elementary steps indicated that the rate-limiting step for NO reduction with CO was the NO dissociation step.

Zr/HZSM-5 catalyst for NO reduction by C2H2 in lean-burn conditions

Abstract Zr-based zeolite catalysts were investigated for the first time in selective catalytic reduction of NO by hydrocarbon (HC-SCR). Highly dispersed zirconium species, especially the amorphous ultrafine zirconium oxide in the catalyst, considerably enhanced the activity for selective catalytic reduction of NO by acetylene (C 2 H 2 -SCR), both by accelerating the NO oxidation to NO 2 and enlarging the NO 2 adsorption capacity of the catalyst under the reaction conditions. Thus a durable and active Zr/HZSM-5 catalyst giving 89% of NO conversion to N 2 at 350 °C in 1600 ppm NO, 800 ppm C 2 H 2 , and 9.95% O 2 in helium was obtained. For the C 2 H 2 -SCR of NO, it was suggested that acidic sites with strong acidity on the Zr-based HZSM-5 catalysts are indispensable to initiate the aimed reaction via the route of NO oxidation to NO 2 , which explains the higher activity for the reaction obtained over the Zr/HZSM-5 catalyst sample with lower SiO 2 /Al 2 O 3 ratio. The zirconium species could only functioned in the presence of protons in the C 2 H 2 -SCR of NO, so a synergistic effect between the zirconium species and protons of the Zr/HZSM-5 catalyst was proposed.

Gold supported on surface acidity modified ZSM-5 for SCR of NO with propene

Au/ZSM-5 prepared by a deposition-precipitation (DP) method has shown good activity for selective catalytic reduction of NO by propene under oxygen-rich atmosphere, and water vapor in the feed stream could greatly enhance NO conversion at low reaction temperatures.

Interface science for optimizing the size of oxidic nanoparticles in supported catalysts

In the present work we attempt to optimize the size of the supported “molybdenum oxide”/titania and “cobalt oxide”/γ-alumina nanoparticles formed after calcination by “selecting”, respectively, the proper mode of deposition and the local structure of the deposited species achieved upon the impregnation step of catalyst preparation. Concerning the first system, it was found that the disubstituted Mo inner sphere surface complexes, which are bound on the support surface stronger than the monosubstituded ones, resist more effectively to the sintering taking place during calcination where the above complexes are transformed progressively into MoO 3 supported nanoparticles. This leads to a catalyst with very small MoO 3 nanoparticles and thus with very high activity for the selective reduction of NO by NH 3. Concerning the “cobalt oxide”/γ-alumina catalysts, it was found that a relatively large (small) size of the supported nanocrystallites is imposed by the bulk deposition (formation of inner sphere surface complexes). A quite small size of the supported “cobalt oxide” nanocrystallites, not strongly interacted with the support surface, is imposed by the interface precipitation. This is the optimum supported phase for the complete oxidation of benzene.

An investigation of NO/CO reaction over perovskite-type oxide La 0.8Ce 0.2B 0.4Mn 0.6O 3 (B = Cu or Ag) catalysts synthesized by reverse microemulsion

The perovskite-type oxides La 0.8Ce 0.2Cu 0.4Mn 0.6O 3 and La 0.8Ce 0.2Ag 0.4Mn 0.6O 3 prepared by reverse microemulsion and sol–gel methods (denoted as R and S, respectively), have been investigated on their catalytic performance for the (NO + CO) reaction, and characterized by means of temperature-programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). XRD measurements proved the presence of the perovskite phase with a considerable amount of CeO 2 phase and the formation of CeO 2 phase was restrained with the reverse microemulsion method. TEM investigations revealed that the La 0.8Ce 0.2Cu 0.4Mn 0.6O 3-R nanoparticles were uniform spheres in shape with diameters ranging from 40 to 50 nm, whereas an aggregation of particles was found for the La 0.8Ce 0.2Cu 0.4Mn 0.6O 3-S catalyst. The activity of NO reduction with CO decreased in the order of La 0.8Ce 0.2Cu 0.4Mn 0.6O 3-R > La 0.8Ce 0.2Cu 0.4Mn 0.6O 3-S > La 0.8Ce 0.2Ag 0.4Mn 0.6O 3-R > La 0.8Ce 0.2Ag 0.4Mn 0.6O 3-S. In NO-TPD experiments, the principal desorbed species detected in the effluent was NO with a trace amount of O 2 and N 2O, suggesting that the non-dissociated adsorption of NO on the surface of the perovskite-type oxides was dominant. The XPS results revealed that Ce 4+ and Cu + was the predominant oxidation state for Ce and Cu components in La 0.8Ce 0.2Cu 0.4Mn 0.6O 3 and La 0.8Ce 0.2Ag 0.4Mn 0.6O 3 catalysts. The existence of Cu + ions and its redox reaction (Cu + ↔ Cu 2+) would benefit the NO adsorption and reduction by CO.

Hydrogen assisted urea-SCR and NH3-SCR with silver–alumina as highly active and SO2-tolerant de-NOx catalysis

Addition of 0.5% H2 in the selective catalytic reduction of NO by urea (urea-SCR) caused a drastic improvement of NO reduction activity of Ag/Al2O3. Among various silver-based catalysts Ag/Al2O3 showed highest activity for H2 assisted urea-SCR, and high NO conversion (above 84%) and no formation of N2O were achieved over wide temperature range (200–500°C) at GHSV of 75,000h−1. After H2 assisted urea-SCR at 250°C with 10% H2O and 50ppm SO2 under GHSV of 380,000h−1 for 24h, NO conversion over Ag/Al2O3 decreased from 48 to 30%, though original activity was recovered when the deactivated catalyst was heated at 500°C in the urea-SCR condition for 1h. The catalyst also showed high SO2-tolerance in H2 assisted NH3-SCR at 200°C.

ITO electrode modified with chitosan nanofibers loading polyoxometalate by one step self-assembly method and its electrocatalysis

Chitosan is a cationic biopolymer that has many electrochemical applications because of its ability to interact with anionic surface-active molecules. In present experiment, chitosan nanofibers were successfully deposited on indium tin oxide (ITO) substrates by electrospinning chitosan solution. After neutralization with saturated Na 2CO 3 aqueous solution to maintain its fibrous structure, α-[P 2W 18O 62] 6− (abbr. P 2W 18) was immobilized on the chitosan nanofibers by one step self-assembly technique. The scanning electron microscope (SEM) images showed that P 2W 18 was mainly deposited on chitosan nanofibers. The cyclic voltammetric responses showed three well redox couples of P 2W 18. Electrochemical behavior of the electrode prepared under different condition of pH value was investigated. In addition, the modified electrode exhibited high electrocatalytic activity for reduction of NO 2 - .

Creation of Redox Adsorption Sites by Pd2+Ion Substitution in nanoTiO2for High Photocatalytic Activity of CO Oxidation, NO Reduction, and NO Decomposition

The present study aims at developing a new photocatalyst for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in titania. For this purpose, Pd ion-substituted TiO2, Ti1-xPdxO2-δ, was synthesized for the first time by solution combustion method. The photocatalytic activity was investigated with increasing Pd substitution and the optimum concentration was found to be 1 atom % Pd ion in TiO2. The reduction of NO was carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd2+ sites, the reduction of NO was 2 orders of magnitude higher than unsubstituted TiO2. High rates of photooxidation of CO with O2 over Ti1-xPdxO2-δ are observed at room temperature. It was shown that enhanced CO oxidation at Pd2+ ion site and O2 or NO photo dissociation at oxide ion vacancy is responsible for the enhanced catalytic activity.

NO reduction by CO in the presence of water over gold supported catalysts on CeO2-Al2O3 mixed support, prepared by mechanochemical activation

The reduction of NO by CO was studied on gold catalysts supported on ceria-alumina, prepared by mechanochemical activation. The samples were characterized by means of XRD, TPR, XPS and Raman spectroscopy. The influence of water in the feed on the catalytic activity was evaluated as well. It was established that the addition of hydrogen and water improves NO reduction activity by CO. The role of water was connected to the hydrogen production by WGS. The role of oxygen vacancies created in ceria structure in the presence of alumina was also discussed. The 100% selectivity to N2 at about 200°C was kept in all cases of catalytic measurements, making the studied gold catalysts promising for practical application.

Effects of catalyst aging on the activity and selectivity of commercial three-way catalysts

A Pd catalyst is particularly effective for the oxidation of CO and C3H6 at low temperatures, while the Pt/Rh/Ce catalyst is active for NO reduction. The TWC activity of both catalysts generally decreased as the catalyst mileage increased. However, the NO reduction activity was less affected by catalyst aging compared to the oxidation reactions. The selectivity of the catalysts in favor of the CO–O2 reaction (vs. C3H6–O2 reaction) in the O2 partitioning experiments became less pronounced as the catalyst aged. The NO partitioning experiments reveal the superior capability of H2 in NO reduction to the other reductants (CO and C3H6) examined in the present study. The reactivities of NO with both H2 and CO were found to decrease upon catalyst aging, resulting in decreased overall NO removal activity.

Nitrogen doping of activated carbon loading Fe2O3 and activity in carbon-nitric oxide reaction

Nitrogen doping of activated carbon loading Fe2O3 was performed by annealing in ammonia, and the activity of the modified carbon for NO reduction was studied in the presence of oxygen. Results show that Fe2O3 enhances the amount of surface oxygen complexes and facilitates nitrogen incorporation in the carbon, especially in the form of pyridinic nitrogen. The modified carbon shows excellent activity for NO reduction in the low temperature regime (<500 °C) because of the cooperative effect of Fe2O3 and the surface nitrogen species.

Templated synthesis and catalytic properties of an Rh/ceria-zirconia catalyst

Ceria-zirconia nanophase with structural defects and high thermal stability was synthesized by a surfactant-templated method. The 0.5 wt.% Rh/ceria-zirconia catalyst shows high activity for NO reduction by CO under an oxygen-rich condition, and the selectivity to 100% N2 below 200°C was achieved.

Synthesis and characterization of mesoporous Mn/Al-SBA-15 and its catalytic activity for NO reduction with ammonia

Al-SBA-15 was prepared by one-step hydrothermal synthesis method, and was characterized by X-ray diffraction, N 2 -adsorption, transmission electron microscope and Fourier infrared spectra of chemisorbed pyridine (Py-IR). The results showed that Al-SBA-15 had well-ordered hexagonal mesopores. As compared with Si-SBA-15, Al-SBA-15 had thicker pore wall, higher surface area, and stronger Lewis acidity. Due to the stronger Lewis acidity, Mn/Al-SBA-15 catalyst prepared by impregnation showed better activity than Mn/Si-SBA-15 in the selective catalytic reduction of NO by NH 3 .

Effects of precursors on the surface Mn species and the activities for NO reduction over MnO /TiO2 catalysts

Abstract TiO2-supported manganese oxide catalysts were prepared from two different precursors, manganese nitrate (MN) and manganese acetate (MA), and these samples were characterized by BET, XRD, TG/DTA, XPS and FT–IR. The characterization results showed that the MN precursor resulted primarily in MnO2, accompanied with some Mn-nitrate, while the MA precursor caused mainly Mn2O3 species. These two different precursors also led to different surface Mn atom concentrations indicated by XPS and NH3 adsorption. Consequently, the higher low-temperature activity of MnOx/TiO2 from MA precursor was attributed to higher surface Mn concentration and the surface Mn2O3 species.

Influence of Al2O3 support on the activity of Ag/Al2O3 catalysts for SCR of NO with decane

The role of the Al2O3 support on the activity of supported Ag catalyst towards the selective catalytic reduction (SCR) of NO with decane is elucidated. A series of Ag/Al2O3 catalysts were prepared by impregnation method and characterized by N2 pore size distribution, XRD, UV–Vis, in-situ FT-IR and acidity measurement by NH3 and pyridine adsorption. The catalytic activity differences of Ag/Al2O3 are correlated with different properties of Al2O3 supports and the active Ag species formed. 4wt% Ag supported on sol-gel prepared Al2O3 (Ag/Al2O3 (SG), showed higher NOx conversion (65% at 400 °C), compared with the respective catalysts made from commercial Al2O3 (Ag/Al2O3 (GB), Ag/Al2O3 (ALO), (∼26 and 7% at 400 °C). The higher surface area, acidity and pore size distribution in sol–gel prepared Al2O3 (SG) results in higher NO and hydrocarbon conversion. Based on the UV–vis characterization, the activity of NO reduction is correlated to the presence of Agnδ+ clusters and acidity of Al2O3 support was found to be one of the important parameter in promoting the formation and stabilization of Agnδ+ clusters. Furthermore from pyridine adsorption results, presence of more number of Bronsted acid sites in Ag/Al2O3 (SG) is confirmed, which could also contribute to low temperature hydrocarbon activation and improve NO conversion. In situ FT-IR measurements revealed the higher rate of –CN and –NCO intermediate species formation over 4wt% Ag/Al2O3 (SG). We conclude that the physico–chemical properties of Al2O3 play a crucial role in NOx conversion over Ag/Al2O3 catalysts. Thus, the activity of the Ag/Al2O3 catalyst can be tailored by using a proper type of Al2O3 support.

Direct electrochemical behavior of cytochrome c on DNA modified glassy carbon electrode and its application to nitric oxide biosensor

Cytochrome c/DNA modified electrode was achieved by coating calf thymus DNA onto the surface of glassy carbon electrode firstly, then immobilizing cytochrome c on it by multi-cyclic voltammetric method and characterized by the electrochemical impedance. The electrochemical behavior of cytochrome c on DNA modified electrode was explored and showed a quasi-reversible electrochemical redox behavior with a formal potential of 0.045 ± 0.010 V ( versus Ag/AgCl) in 0.10 M, pH 5.0, acetate buffer solution. The peak currents were linearly with the scan rate in the range of 20–200 mV/s. Cytochrome c/DNA modified electrode exhibited elegant catalytic activity for the electrochemical reduction of NO. The catalytic current is linear to the nitric oxide concentration in the range of 6.0 × 10 −7 to 8.0 × 10 −6 M and the detection limit was 1.0 × 10 −7 M (three times the ratio of signal to noise, S/N = 3).