Presence Of Excess Oxygen Research Articles

Fluorite-like phases in the La2MoO6 – Sm2MoO6 – MoO3 system: Homogeneity region, crystal structure, and conductive properties

Samples in the La2MoO6 – Sm2MoO6 – MoO3 system were obtained using the solid-state synthesis method. The phase formation in the given compositional section was firstly studied, and the homogeneity region of the fluorite-like lanthanum-samarium molybdate was determined, as confirmed by XRD analysis including Rietveld refinement and SEM with energy-dispersive microanalysis. The fluorite-like phase contains less molybdenum than the isostructural neodymium molybdate Nd5Mo3O16+δ. The homogeneity region of fluorite-like solid solutions has been determined, which corresponds to the La5-xSmxMo2.75O15.75 section in the composition range 2.5 ≤ x ≤ 3.5. The crystal structure is characterized by the splitting of cation positions and the presence of excess oxygen in the octahedral voids of the structure. Oxygen atoms in the octahedral positions are displaced from the center of the voids and enter into the molybdenum coordination sphere. The density of single-phase ceramic samples increases with the increase in samarium content. The conductive properties of single-phase ceramics were investigated in an air atmosphere using impedance spectroscopy. The total conductivity was ∼10−2 S cm−1 for La2.5Sm2.5Mo2.75O15.75 at 800 °C. The grain bulk conductivity exhibits a break at a temperature of approximately 600 °C, which may be explained by the depletion of charge carriers in the structure.

Computational study of palladium percentage and oxygen ratio effects on air-methane catalytic combustion in a helical microchannel: A molecular dynamics approach

Combustion is an exothermic chemical process between an explosive substance and an oxidizing agent that is accompanied by heat generation and chemical change of raw materials. Catalysts are used in a combustion process for various reasons, including the speed at which the material reaches equilibrium. Catalysts are chemicals that increase the rate of reaction in chemical processes. The present research investigates the influence of palladium percentage and oxygen ratio on air-methane catalytic combustion in a helical microchannel. For this purpose, the atomic behavior and combustion performance of the simulated sample in the presence of excess oxygen and oxygen deficiency is reported by the molecular dynamics (MD) method. The potential functions used in this paper were Lennard-Jones, the embedded atom model (EAM), and Coulomb. It is concluded that increasing palladium percentage in limited ratios improves the atomic and combustion performance of the simulated structure, and this enhancement is greater in the presence of excess oxygen. In the presence of excess oxygen, the numerical value of maximum density, velocity and temperature converged from 0.138 atom/Å3, 0.33 Å/ps and 523 K to 0.144 atom/Å3, 0.36 Å/ps and 539 K, respectively with increasing palladium percentage from 1 % to 4 %. And by increasing the palladium ratio to 10 %, these numerical values decrease to 0.137 atom/Å3, 0.31 Å/ps and 530 K. Moreover, in the presence of oxygen deficiency, heat flux, thermal conductivity, and combustion efficiency of atomic samples reached 2049 W/m2, 1.23 W/m.K and 90 % after rising palladium to 4 %, and it decreased to 2035 W/m2, 1.19 W/m.K and 86 % by adding 10 % palladium. Therefore, the results indicate that the oxygen and the catalyst (palladium) ratios can benefit the combustion process. These results can optimize the atomic performance and combustion performance of structures essential for use in various industries.

Transition metal modified Mn-based catalysts for CO-SCR in the presence of excess oxygen

The CO-SCR technology based on transition metal is of great significance for NOx removal in large-scale industrial production. However, excess oxygen usually hinders the deNOx reaction in the actual industrial process. In this paper, a series of Mn-based catalysts modified by transition metals (Fe, Ni, Cu) were prepared using the co-precipitation method, which aimed to obtain good CO-SCR performance under O2-rich condition. The results showed that the Cu-Mn2 sample exhibited excellent deNOx performance. Regardless of the presence or absence of oxygen, the NO conversion of Cu-Mn2 catalyst was remain about 60% and 95% at 350 and 400 ℃, respectively. Differently, the NO conversion of Fe-Mn2 catalyst significantly increased from approximately 10% to 61% at 400 ℃ after introducing oxygen, which proved that excess oxygen could promote the CO-SCR process over Fe-Mn2 sample. The varied physical and chemical properties of the prepared materials were thoroughly evaluated through BET, SEM, XRD, XPS and in situ DRIFTS technologies. The results demonstrated that perovskite α-Mn2O3, decahedral Mn5O8, Fe2O3 and Fe3O4 crystals were the dominant structures promoting deNOx reaction on the Fe-Mn2 catalyst. The oxidation of low valence nitrogen oxides by decahedral Mn5O8 on Fe-Mn2 catalyst was an important factor for oxygen resistance. And the various spinel structures over Ni-Mn2, and Cu-Mn2 indicated strong synergistic effects. For the Cu-Mn2 catalyst, the strong synergistic effect of Cu-□-Mn species could promote the dissociation of intermediate -NONO. O2 tended to occupy the surface synergetic oxygen vacancies in Cu-□-Mn species at high temperatures, which could inhibit the dissociation of -NONO and enhance the CO oxidation reaction. The possible reaction mechanisms for CO-SCR over Mn-based catalysts were discussed specifically.

Effect of alkali addition on a Cu/SmCeO2 @TiO2 catalyst for NO reduction with CO under oxidizing conditions

The accumulation of alkali metals generated during biomass combustion onto the catalysts employed for off-gas treatment can have a detrimental effect on their performance. This work investigates the effect of potassium as a model alkali on an efficient copper-based catalyst supported on SmCeO2 @TiO2. The addition of potassium modifies the redox properties of the Cu species or, more specifically, the metal-ceria interface, providing better catalytic activity for NO reduction in oxidizing conditions. SmCeO2 @TiO2 stabilizes highly dispersed copper species, and the presence of potassium introduces surface distortions that modify the lability of oxygen atoms. The results demonstrate the key role of surface defects and labile oxygen species associated with the CeO2 support. It was found that both Cu/SmCeO2 @TiO2 and K/Cu/SmCeO2 @TiO2 catalysts fully oxidized CO below 350 °C and actively reduced NO with CO in the presence of excess oxygen, reaching a maximum NO conversion of 65% at 316 °C and 83% at 330 °C, respectively, while undesired NO2 release was minimized in the alkaline-loaded sample.

Structural and electronic properties with respect to Si doping in oxygen rich ZnSnO amorphous oxide semiconductor

The effect of Si doping in the presence of excess oxygen on the zinc-tin-oxide (ZTO) thin-film transistor is investigated. The threshold voltage increases from 3.86 to 10.8 V, and the ON current reduces from 4 × 10 -4 to 1.1 × 10 -4 A for the undoped and 1 wt% Si-doped ZTO transistor, respectively. The changes in the threshold voltage and the ON current are attributed to the suppression of free charge carriers due to excess oxygen in the film. The annihilation of oxygen vacancy-related defects states is substantiated by the density of states extracted from the photonic capacitance-voltage characteristic of the undoped and Si-doped ZTO thin-film transistors. Moreover, due to the high binding energy of Si and oxygen, excess oxygen is introduced into the film. The excessive oxygen forms the O-O ex dimer that acts as the electron trap and degrades the device's stability. From the bias stress measurement and the density of states extraction, it is concluded that 0.5 wt% doping of Si in ZTO is optimal for moderate device performance, less defects density, and high stability.

Chemical cyanide treatment of polycrystalline p-Cu2O/n-ZnO solar cell

Cuprous oxide (Cu2O) and zinc oxide (ZnO) hold a very crucial position in the field of materials research because of their immense potential in many acoustic, electronic and optical applications. Cu2O is a direct-gap semiconducting material with forbidden energy gap around 2.0 eV. It has been considered as one of the most promising materials for photovoltaic applications, especially for use at the top in a cascade cell structure. The enchantment of Cu2O and ZnO as photovoltaic materials is due to fact that their constituent materials are nontoxic, abundantly available and of relatively low cost. In this work, Cu2O thin films in polycrystalline form were prepared in radio-frequency (rf) reactive magnetron sputtering route on glass substrates at different substrate temperatures. After the samples were prepared, these were taken through a crown-ether cyanide (CN) treatment. Presence of oxygen in excess compared to stoichiometry is the major active impurity in Cu2O and consequently holes are the majority charge carriers in it. With the aid of crown-ether cyanide treatment of the prepared samples, hole-mobility was found to increase and resistivity was found to decrease considerably. Finally, polycrystalline p-Cu2O/n-ZnO heterojunctions were fabricated for use in solar cells. Results of Hall measurement strongly support the observations made from DLTS studies and photocurrent measurements. Thus, our present study confirms the improvement of device performance of the p-Cu2O /n-ZnO heterojunctions on chemical cyanide treatment.

Understanding ammonia and nitrous oxide formation in typical three-way catalysis during the catalyst warm-up period

Ammonia (NH3) and nitrous oxide (N2O) have been regarded as the typical secondary pollutants emitted from vehicles equipped with a three-way catalyst (TWC). MultiGas FT-IR Analyzer was applied to determine the outlet gas concentrations in the light-off experiments, in order to understand how different reaction conditions and catalyst aging affect the production of these two pollutants. It was found that N2O formation is favored by the existence of excess oxygen during NO reduction, whereas NH3 is readily formed within the lack of reactive oxygen species. Interestingly, the reduction of NO by H2 in presence of excess oxygen can also lead to NH3 formation when the active metal particles are large enough, which provides the rational explanation why the increased NH3 was emitted from older gasoline vehicles. The loss of the catalytically active sites and reducibility caused by thermal aging requires longer time to warm-up thereby favors the N2O and NH3 formation, which is the major reason for the higher CO, NOx, HC, N2O and NH3 emissions from the old gasoline vehicles than that of low-mileage gasoline vehicles.

Insight into highly efficient FeOx catalysts for the selective catalytic reduction of NOx by NH3: Experimental and DFT study

Fe3O4, α-Fe2O3 and γ-Fe2O3 catalysts were synthesized and showed excellent activities for the selective catalytic reduction (SCR) of NOx by NH3 in the temperature range that was between 433 K and 653 K in the presence of excess oxygen. Physical and chemical properties of catalysts were tested to investigate the effect of the iron oxides on the NH3-SCR activities by a series of characterization methods that were XRD, H2-TPR, NH3-TPD, BET and XPS. The related results indicated that the species of iron oxides had significant effects on oxidation–reduction ability, surface acidity distribution, BET surface area and surface adsorbed oxygen. Meanwhile, DRIFTS tests were carried out to further investigate the reduction process over α-Fe2O3, γ-Fe2O3 and Fe3O4 catalysts, supporting the DFT calculations. The adsorption energy of ammonia and nitric oxide on α-Fe2O3 (001), γ-Fe2O3 (001) and Fe3O4 (111) surfaces are calculated by the Density Functional Theory (DFT) calculations, suggesting that ammonia and nitric oxide are easily adsorbed on the Fe3O4 (111) surface. Moreover, it is reasonable to draw a conclusion that more surface chemisorbed oxygen, easier adsorption of reaction gases (NO, NH3 and O2) and more effortless oxidative dehydrogenation process can promote NH3-SCR.

Synthesis of Carbon Nanoparticles with Cobalt-Rich Shell via Pyrolysis of Zn-ZIF@Co/Zn-ZIF: Relevance of Co(III) Precursors

To the best of our knowledge, this is the first report on the rapid one-pot synthesis of a unique core-shell-structured zeolitic imidazolate framework (ZIF) using Co(III) and Zn(II) precursors. The key to obtaining this unique structure is the use of a Co(III) precursor as the starting material. Transmission electron microscopy (TEM) reveals that Co was present within a 30-nm-thick shell layer of the ZIF material. Thermal decomposition of the ZIF material affords core-shell-structured carbon nanoparticles that have Co on the external surface of the carbon grain. We have previously demonstrated that this carbonaceous material obtained by thermal decomposition exhibited high performance as an adsorbent for nitric oxide, even in the presence of excess oxygen and water vapor, and therefore, it was a suitable material for NOx elimination at low temperatures. The growth mechanism of the synthesized ZIF particles and the differences between synthesized ZIF and conventional Co(II)-ZIF-67 are discussed. The reactivity of the Co(III) precursor is much lower than that of the Co(II) species, leading to slower precipitation of Co(III) than that of Zn(II), thus forming the core-shell structure.

Kinetics of the Reactions of CH2OO with Acetone, α-Diketones, and β-Diketones

Rate constants for the reactions between the simplest Criegee intermediate, CH2OO, with acetone, the α-diketones biacetyl and acetylpropionyl, and the β-diketones acetylacetone and 3,3-dimethyl-2,4-pentanedione have been measured at 295 K. CH2OO was produced photochemically in a flow reactor by 355 nm laser flash photolysis of diiodomethane in the presence of excess oxygen. Time-dependent concentrations were measured using broadband transient absorption spectroscopy, and the reaction kinetics was characterized under pseudo-first-order conditions. The bimolecular rate constant for the CH2OO + acetone reaction is measured to be (4.1 ± 0.4) × 10-13 cm3 s-1, consistent with previous measurements. The reactions of CH2OO with the β-diketones acetylacetone and 3,3-dimethyl-2,5-pentanedione are found to have broadly similar rate constants of (6.6 ± 0.7) × 10-13 and (3.5 ± 0.8) × 10-13 cm3 s-1, respectively; these values may be cautiously considered as upper limits. In contrast, α-diketones react significantly faster, with rate constants of (1.45 ± 0.18) × 10-11 and (1.29 ± 0.15) × 10-11 cm3 s-1 measured for biacetyl and acetylpropionyl. The potential energy surfaces for these 1,3-dipolar cycloaddition reactions are characterized at the M06-2X/aug-cc-pVTZ and CBS-QB3 levels of theory and provide additional support to the observed experimental trends. The reactivity of carbonyl compounds with CH2OO is also interpreted by application of frontier molecular orbital theory and predicted using Hammett substituent constants. Finally, the results are compared with other kinetic studies of Criegee intermediate reactions with carbonyl compounds and discussed within the context of their atmospheric relevance.

In Situ X-Ray Absorption Spectroscopy Studies of Carbon Monoxide Oxidation in the Presence of Nanocomposite Cu–Fe–Al Oxide Catalysts

Nanocomposite Fe–Al and Cu–Fe–Al oxide catalysts are studied in the CO oxidation reaction. It is shown that the introduction of copper leads to a more than two orders of magnitude increase in the reaction rate. The most active catalyst is a nanocomposite containing 5 wt % CuO, 78 wt % Fe2O3, and 17 wt % Al2O3. According to X-ray diffraction analysis, the catalysts consist of hematite nanoparticles, α-Fe2O3, and amorphous alumina. Copper is in a highly dispersed state to form CuO and CuFeOx clusters. Results of in situ X‑ray absorption spectroscopy studies suggest that the reduction of copper from Cu2+ to Cu1+ and Cu0 in a CO stream begins at a temperature of 200–250°C; at 400–600°C, copper is mostly in the metallic state; the Fe3O4 → FeO → Fe reduction begins at 400–500°С. In a stoichiometric mixture of CO and O2, Fe3+ does not undergo reduction; the reduction of copper oxide to metal occurs at temperatures above 400°C. In the presence of excess oxygen in a temperature range of 100–600°C, no changes in the chemical state of the catalysts are detected. The mechanism of CO oxidation in the presence of Cu–Fe–Al nanocomposites is proposed.

An electrochemical study of cobalt-salen (N,N′-bis(salicylidene)ethylenediaminocobalt(II) in the oxidation of syringyl alcohol in acetonitrile

The reactivity of cobalt(II) complexes with molecular oxygen is a heavily studied and extremely important catalytic system. These interactions result in the formation of metal-dioxygen adducts that are responsible for numerous cobalt-catalyzed oxidations. In the case of 4-coordinate cobalt salen [Co(salen)] complexes, the formation of catalytically active, mononuclear, superoxo adducts in the presence of a secondary, N-donor ligand has been demonstrated [Co(salen)pyr-O2]. In batch reactions, these adducts are known to readily oxidize certain para-substituted phenolic compounds resulting in benzoquinones in high yield. Para-phenolic model compounds have been used to demonstrate the potential use of cobalt Schiff base complexes in the oxidation of lignin biomass. This work investigates the redox behavior of the Co(salen)pyr-O2 adduct as a potential recyclable electrocatalyst. Using traditional electrochemical techniques, the activity of the Co(salen)pyr-O2 adduct is evaluated as it applies to the oxidation of the substrate syringyl alcohol (4-(hydroxymethyl)-2,6-dimethoxy-phenol) in acetonitrile. Typical EC′ electrochemical behavior is reported showing a near linear relationship between substrate concentration and peak current density (Jp) up to 200 mV s−1. Electrochemical titration of catalytic amounts of Co(salen) with pyridine in the presence of excess oxygen and substrate indicate that the one-electron oxidation of Co(salen)pyr-O2H is reversible up to 2:1 pyridine to cobalt. However EPR characterization of electrolysis experiments with Co(salen)pyr-O2 in the presence of excess substrate show evidence for the deactivation of the catalyst system after two hours, indicating possible poor ligand stability or the occurrence of an inhibiting side reaction under reaction conditions.

Microkinetic Modeling of the Oxidation of Methane Over PdO Catalysts—Towards a Better Understanding of the Water Inhibition Effect

Water, which is an intrinsic part of the exhaust gas of combustion engines, strongly inhibits the methane oxidation reaction over palladium oxide-based catalysts under lean conditions and leads to severe catalyst deactivation. In this combined experimental and modeling work, we approach this challenge with kinetic measurements in flow reactors and a microkinetic model, respectively. We propose a mechanism that takes the instantaneous impact of water on the noble metal particles into account. The dual site microkinetic model is based on the mean-field approximation and consists of 39 reversible surface reactions among 23 surface species, 15 related to Pd-sites, and eight associated with the oxide. A variable number of available catalytically active sites is used to describe light-off activity tests as well as spatially resolved concentration profiles. The total oxidation of methane is studied at atmospheric pressure, with space velocities of 160,000 h−1 in the temperature range of 500–800 K for mixtures of methane in the presence of excess oxygen and up to 15% water, which are typical conditions occurring in the exhaust of lean-operated natural gas engines. The new approach presented is also of interest for modeling catalytic reactors showing a dynamic behavior of the catalytically active particles in general.

Thermal conductivity variation in uranium dioxide with gadolinia additions

By combining experimental observations on Gd doped fuel with a theoretical understanding, the variation in thermal conductivity with Gd concentration and accommodation mechanism has been modelled. Four types of Gd accommodation mechanisms have been studied. In UO2−x, isolated substitutional Gd3+ ions are compensated by oxygen vacancies and {2GdU’:VO⋅⋅}× defect clusters. In UO2, isolated substitutional Gd3+ ions are compensated by U5+ ions and {GdU’:UU⋅}× defect clusters. The results indicate that defect clusters can be considered as less effective phonon scatterers and therefore result in less thermal conductivity degradation. The thermal conductivity predicted for UO2 with {GdU′:UU⋅}× defect clusters is in good agreement with experimental data for UO2 with 5 wt% Gd2O3. This supports the previous theoretical results that Gd is accommodated through defect clusters {GdU’:UU⋅}× in UO2 in the presence of excess oxygen.

Theory and practice of metal oxide catalyst design for the selective catalytic reduction of NOx with NH3

For NOx control in the presence of excess oxygen, selective catalytic reduction with ammonia (NH3-SCR) has been successfully applied in the purification of coal-fired flue gas and diesel vehicle exhaust on a large scale. For both cases, various NH3-SCR catalysts have been developed, with the incorporation of desirable catalytic properties being the central issue. However, the fundamental principle for designing NH3-SCR catalysts with high activity, selectivity, and stability remain unclear. Generally, in the NH3-SCR reaction, the redox and acid sites on the catalyst are prerequisites that need to work together. Therefore, the close coupling of these dual functional sites is imperative for the design of NH3-SCR catalysts with high NOx removal efficiency. Taking this intrinsic principle into account, we successfully designed and developed various novel catalysts with excellent NH3-SCR performance. This review will focus on the theory and practice of designing metal oxide catalysts for NH3-SCR.

Effect of oxide supports on palladium based catalysts for NO reduction by H2-SCR

The present work shows the synthesis of various mixed oxide catalysts prepared by co-precipitation followed by impregnation of palladium metal. The catalysts are denoted as Pd/MgO-CeO2, Pd/ZrO2-CeO2, Pd/Al2O3-CeO2, and Pd/TiO2-CeO2 and examined for selective catalytic reduction (SCR) of NO with H2 in the presence of excess oxygen (6% O2). The properties of catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET, transmission electron microscopy (TEM), H2-temperature-programmed reduction (H2-TPR), and Raman spectroscopy. The synthesized catalysts exhibit notable NO reduction potential at 175 ℃ and in a wide temperature range from 100 to 400 ℃. Compared to bare CeO2 support, the Pd/ZrO2-CeO2 catalyst greatly enhances the SCR activity with a wide temperature range (100–400 ℃). The experimental results showed that the Pd/ZrO2-CeO2 catalyst had the best catalytic activity with 92 % NO reduction and a wide temperature reduction window (150–400 ℃) at the gas hour space velocity (GHSV) of 20,000 h−1.

The influence of support composition on the activity of Cu:Ce catalysts for selective catalytic reduction of NO by CO in the presence of excess oxygen

Excellent catalytic performance for NO reduction by CO in the presence of 5% O2over Cu1:Ce3/Al2O3.

A new sol‐gel route alumina for selective oxidation of H2S to sulphur

AbstractIn this study, a new synthesis method was developed for the production of modified sol‐gel alumina (SG‐M) for the selective oxidation of H2S to elemental sulphur. The catalytic activity of this modified alumina without any active metal incorporation was then compared with the activity of commercial alumina (alumina‐com) for H2S selective oxidation. The N2 adsorption‐desorption isotherm showed that the SG‐M alumina synthesized in this work has a mesoporous structure with well‐defined hysteresis loops. Both alumina materials showed a γ‐Al2O3 crystalline phase with an amorphous structure in their crystal structure. The surface acidity of the alumina materials was determined using pyridine‐adsorbed FTIR analyses, and both alumina showed Lewis acid sites on their surfaces. The catalytic activity tests were performed at 250°C using a feed ratio of O2/H2S:0.5. The complete conversion of H2S over SG‐M was achieved during 400 minutes of reaction time. However, the commercial alumina lost its activity at earlier reaction times. Lewis acid sites and surface hydroxyl groups caused the alumina to be active in H2S selective catalytic oxidation, and the formation of Al‐S bonds, observed when the H2S conversion fell, caused a decrease in the catalytic activity of the alumina materials. A high sulphur yield (≥95%) was obtained over SG‐M, even though there was no active metal incorporation and even in the presence of excess oxygen. Considering the catalytic activities, the new sol‐gel alumina synthesized in this work is superior to commercial alumina. It was concluded that, as a catalyst without any active metal, SG‐M is a promising catalyst in H2S selective oxidation to sulphur.

Reaction Kinetics of Cyanide Binding to a Cobalt Schiff-Base Macrocycle Relevant to Its Mechanism of Antidotal Action.

The Co(II/III)-containing macrocycle, cobalt 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(17)2,11,13,15-pentaenyl cation, or CoN4[11.3.1], is a potential cyanide-scavenging agent. The rate of reduction of Co(III)N4[11.3.1] by ascorbate is reasonably facile under pseudo-first-order conditions; a second-order rate constant of 11.7(±0.4) M-1 s-1 was determined at 25 °C and pH 7.4, along with the activation parameters for the reaction (ΔH⧧ = 53.9(±0.8) kJ mol-1; ΔS -79(±3) J mol-1 K-1). It follows that any cyanide-decorporating capability of the cobalt complex should depend more on the cyanide-binding characteristics of Co(II)N4[11.3.1] than the oxidized form. The kinetics of the reaction of cyanide with Co(II)N4[11.3.1] under anaerobic pseudo-first-order conditions is rapid and resulted in a linear dependence on the cyanide concentration, kHCN = 8 × 104 M-1 s-1, with a nonlinear intercept of 420 s-1 at 10 °C, pH 7.6. The observed reaction rate increases significantly with increasing pH. A rate law is suggested, kobs = k'[X] + (kHCN + kCNKa/[H+])[HCN], where kCN is estimated to be ∼2 × 106 M-1 s-1. Activation parameters for the reaction with HCN (ΔH⧧ = 10.7(±0.4) kJ mol-1; ΔS⧧ = -153(±1) J mol-1 K-1) suggest an associative mechanism. In the presence of excess oxygen, i.e., at higher levels than free oxygen in vivo, the reaction rate was too fast to be measured, and the final product was the oxidized complex, Co(III)N4[11.3.1], where any cyanide ligands had been lost. This is much more rapid than the oxidation of the parent compound by oxygen, for which a second-order rate constant of 0.5(±0.02) M-1 s-1 at 25 °C was obtained. The study has gone some way toward enhancing our understanding of the reaction of Co(II)N4[11.3.1] with cyanide. The fast reaction rate implies a high efficacy of the cyanide-scavenging capability of the complex and further supports the suggestion stemming from our previous work that Co(II)N4[11.3.1] could prove to be a better and more cost-effective cyanide antidote than the FDA-approved hydroxocobalamin.

NO-CH4-SCR Over Core-Shell MnH-Zeolite Composites

Selective catalytic reduction of NO with methane (NO-CH4-SCR) in the presence of excess oxygen was investigated over the synthesized MnH-ZZs-n zeolite composite catalysts with FAU (as core) and BEA (as shell) topologies. XRD, SEM, and NH3-TPD technologies were employed to characterize the catalysts. It is found that the topological structure of the zeolite affected the catalytic properties and H2O/SO2 tolerances considerably. MnH-ZZs-n catalysts exhibited much higher NO-CH4-SCR activity than the physical mixture catalysts with comparable relative mass content of Y and Beta zeolites, particularly the ratio of Y and Beta at the range of 0.2–0.5 than the MnH-Beta catalysts with single topology. NH3-TPD results showed that one new type of strong acidic sites formed in H-ZZs-n and remained in MnH-ZZs-n resulted from the interaction between the Lewis and Brönsted acid sites under a particular environment. The special zeolite-zeolite structure with ion-exchanged Mn ions in the core-shell zeolite composite catalysts contributed to the novel NO-CH4-SCR properties.