Investigations on the selectivity of catalytic no reduction by ammonia

The activity and selectivity of V₂O₅/γ-Al₂O₃ catalyst were studied in the catalytic reduction of nitrogen oxide by ammonia. The activity of the catalyst monotonically increases as a function of temperature, however, its selectivity decreases. The DeNOx reaction of nitrogen oxides with ammonia can be described well by a mathematical model, which considers selectivity-decreasing side reactions as well in a wide temperature range (220–420°C).     

Selective catalytic oxidation of ammonia to nitrogen

The activity of catalysts of different nature in ammonia partial oxidation has been studied. Vanadium-titanium, copper-titanium catalysts and copper-substituted zeolites are the most active in the reaction. These catalysts are promising if used as honeycomb monoliths.     

Copper exchanged beta zeolites for the catalytic oxidation of ammonia

Copper exchanged on beta zeolites are extremely active and selective for the catalytic oxidation of ammonia to nitrogen and water and this activity correlates to the ease of reduction of the copper species.     

脉冲CO2激光诱导氨的复相催化氧化反应的研究

本文研究了TEA CO2 激光诱导的复相氨氧化反应.在1:1NH3-O2 混合气体的总压力为5Torr丶激光能量密度低于9J.cm-2 条件下, 只有在激光直接辐照于铂或镍表面上时, 才发生明显的氨氧化反应. 测定了激光频率丶能量密度和脉冲辐照次数反应的影响, 发现这类反应具有较明显的激光频率丶能量密度和脉冲辐照次数对该反应的影响, 发现这类反应具有较明显的激光光频率选择性. 同时, 还讨论了该反应的机理, 认为按 Eley-Rideal 机理解释比较合理.     

New technology for selective catalytic oxidation of ammonia to nitrogen

The selective catalytic oxidation (SCO) of ammonia to N₂ was studied by using a series of noble metal-V₂O₅-WO₃ catalysts supported on titania-silica (TS) prepared by coprecipitation method. In the V₂O₅-WO₃ catalyst system, the use of TS as a support was very effective to enhance catalytic activity compared with TiO₂ or SiO₂ alone. The addition of a slight amount of Pd and Ir to V₂O₅-WO₃/TS catalyst caused also remarkable enhancement of the catalytic activity without decreasing the selectivity to N₂. The present catalysts provide remarkably high catalytic performance for SCO of ammonia to N₂ under the practical reaction conditions for an industrial application.     

Activity enhancement and selectivity change in propene oxidation by the catalytic effect of hot electrons

Catalytic effect of hot-electron flow through a catalyst was investigated for propene oxidation. Increase of overall reaction rate as well as selectivity change were found experimentally during flow of hot electrons and above a certain threshold of current density. Selectivities of 36.4% for propylene oxide and 9% for CO₂ were observed on gold surfaces.     

Kinetics of loss of platinum group metals in catalytic oxidation of ammonia

Basic characteristics of ammonia oxidation catalysts based on platinum metals, their composition, wire diameter, and specific mass are presented. An irrecoverable loss of the catalyst in manufacture of regular nitric acid is demonstrated. The loss of catalysts based on platinum-group metals and the effect of various factors on this loss are considered. The effect of various parameters on the ammonia oxidation process is analyzed and an equation describing the process in which platinum-group metals are lost is derived.     

Reaction-driven surface restructuring and selectivity control in allylic alcohol catalytic aerobic oxidation over Pd

Synchronous, time-resolved DRIFTS/MS/XAS cycling studies of the vapor-phase selective aerobic oxidation of crotyl alcohol over nanoparticulate Pd have revealed surface oxide as the desired catalytically active phase, with dynamic, reaction-induced Pd redox processes controlling selective versus combustion pathways.     

Catalytic oxidation of ammonia on RuO2(110) surfaces: mechanism and selectivity

The selective oxidation of ammonia to either N2 or NO on RuO2(110) single-crystal surfaces was investigated by a combination of vibrational spectroscopy (HREELS), thermal desorption spectroscopy (TDS) and steady-state rate measurements under continuous flow conditions. The stoichiometric RuO2(110) surface exposes coordinatively unsaturated (cus) Ru atoms onto which adsorption of NH3 (NH3-cus) or dissociative adsorption of oxygen (O-cus) may occur. In the absence of O-cus, ammonia desorbs completely thermally without any reaction. However, interaction between NH3-cus and O-cus starts already at 90 K by hydrogen abstraction and hydrogenation to OH-cus, leading eventually to N-cus and H2O. The N-cus species recombine either with each other to N2 or with neighboring O-cus leading to strongly held NO-cus which desorbs around 500 K. The latter reaction is favored by higher concentrations of O-cus. Under steady-state flow condition with constant NH3 partial pressure and varying O2 pressure, the rate for N2 formation takes off first, passes through a maximum and then decreases again, whereas that for NO production exhibits an S-shape and rises continuously. In this way at 530 K almost 100% selectivity for NO formation (with fairly high reaction probability for NH3) is reached.     

Application of a thermochemical selectivity criterion to the catalytic oxidation of butadiene to furan and maleic anhydride

It is shown that the selectivity of furan formation from butadiene is not limited by the C−H bond strengths of the molecules involved and that ring fission energies are not suitable data for the criterion applied.     

The activity and selectivity of catalytic peroxide oxidation of chlorophenols over Cu-Al hydrotalcite/clay composite

Liquid phase catalytic oxidation of chlorophenols (CPs) was carried out over Cu-Al hydrotalcite/clay composite at ambient temperature and pressure using hydrogen peroxide as oxidant. The results showed that the catalyst had high catalytic activity, with complete oxidation of 4-CP within 40 min at 40 °C. The content and position of chlorine on the aromatic ring had significantly different effects on the oxidation rate of CPs, with the rate sequence of phenol > monochlorophenol (MCP) > dichlorophenol (DCP) > trichlorophenol (TCP), 3-CP > 2-CP > 4-CP, and 3,5-DCP > 3,4-DCP > 2,5-DCP > 2,4-DCP > 2,6-DCP. This was ascribed to the interactions among σ-electron withdrawing conductive effect, π-electron donating conjugative effect, and steric hindrance effect of chlorine. It was evidenced that the catalytic peroxide oxidation of CPs in the first step was selective and rate-limiting, where chlorinated 1,4-benzoquinones formed.     

Cyclohexane selective oxidation over metal-organic frameworks of MIL-101 family: superior catalytic activity and selectivity

Mesoporous metal-organic frameworks Cr- and Fe-MIL-101 are highly efficient, true heterogeneous and recyclable catalysts for solvent-free selective oxidation of cyclohexane with molecular oxygen and/or tert-butyl hydroperoxide under mild conditions.     

氨浓度对氨蒸发法制备Pd-Cu/凹凸棒土催化剂常温CO氧化性能的影响

以凹凸棒土(APT)作载体,采用氨蒸发法制备了Pd-Cu/APT催化剂,以CO氧化为探针反应,在连续流动微反应装置上,考察了初始氨浓度对催化剂CO常温催化氧化性能的影响。通过N₂-physisorption、XRD、FT-IR、TEM和H₂-TPR等手段对催化剂的结构和性质进行了表征。结果表明,在较低或过高氨浓度条件下,制备的Pd-Cu/APT中Cu物种均主要以CuO为主,仅有少量Cu₂(OH)₃Cl;适宜的氨浓度有利于稳定Cu₂(OH)₃Cl物相的形成,其薄片状的形貌特征、良好的分散状态以及与Pd物种间较强的相互作用,显著提高了CO催化氧化性能。在空速6 000 h^-1、CO体积分数1.5%、水蒸气体积分数3.3%的反应条件下,Pd-Cu/APT催化剂表现出优异的CO室温催化氧化活性和稳定性。     

On the sensitivity and selectivity of analytical catalytic methods

Summary The oxidation ofp-phenetidine hydrochloride with potassium chlorate and copper(II), iron(III) and vanadium(V) as catalysts has been further investigated. Using that reaction as a model, a method is proposed for a simultaneous increase in the sensitivity and the selectivity of the analytical catalytic reactions. With a suitable complexing agent, one of the catalytically active ions is bound in a complex of higher activity, and thus the sensitivity of the reaction with respect to this ion increases. Simultaneously, the interfering ions form with the same agent very stable catalytically inactive complexes, which therefore can not interfere.

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Zusammenfassung Die Oxydation von p-Phenetidinchlorhydrat mit Kaliumchlorat und Kupfer(II), Eisen(III), Vanadin(V) als Katalysatoren wurde weiter untersucht. An Hand dieser Modellreaktion wurde eine Methode zur gleichzeitigen Steigerung der Empfindlichkeit und der Selektivität katalytischer Reaktionen vorgeschlagen. Mit einem geeigneten Komplexbildner wird eine der katalytisch aktiven Ionenarten zu einem Komplex höherer Aktivität gebunden und infolgedessen die Empfindlichkeit hinsichtlich dieser Ionenart gesteigert. Gleichzeitig werden die störenden Ionen mit demselben Reagens zu sehr stabilen, katalytisch inaktiven Komplexen gebunden, so daß sie die Reaktion nicht mehr stören.

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Résumé On a fait une nouvelle étude de l'oxydation du chlorhydrate dep-phénétidine par le chlorate de potassium avec le cuivre-II, le fer-III et le vanadium-V comme catalyseurs. En prenant cette réaction comme modèle, on a proposé une méthode pour augmenter simultanément la sensibilité et la sélectivité des réactions analytiques catalytiques. Avec un agent complexant bien choisi, l'un des ions présentant une activité catalytique se trouve lié dans un complexe de plus grande activité et la sensibilité de la réaction par rapport à cet ion s'en trouve ainsi accrue. Simultanément, les ions interférents forment avec le même agent des complexes très stables, inactifs vis-à-vis de la catalyse et qui ne peuvent donc pas interférer.

     

Selective catalytic oxidation of ammonia to nitrogen on atomic oxygen precovered Au(111)

We demonstrate ammonia oxidation promoted by an atomic oxygen precovered Au(111) surface. The selectivity of the catalytic oxidation of ammonia to NO or N2 on Au(111) is tunable by the atomic oxygen coverage. We propose that N2 and NO are produced via the recombination reactions of Nad + Nad and Nad + Oad.     

Control of the selectivity in partial oxidation of hydrocarbons

A simple kinetic model for the partial oxidation of hydrocarbons on two types of sites was used to study the factors influencing the selectivity to the desired product. It is possible to increase the selectivity significantly by regulating the ratio of the surface concentrations of partial and deep oxidation sites by a periodic temperature treatment.     

Potentials of gas chromatography in the determination of reaction products in the catalytic oxidation of ammonia to nitrogen(II) oxide

Peculiarities of the determination of nitrogen oxides and ammonia in the reaction products of ammonia oxidation are studied by gas chromatography. Particular attention was paid to the sampling problem. It is shown that in the course of the transportation of samples containing nitrogen(II) oxide and oxygen, the oxidation of nitrogen(II) oxide to nitrogen(IV) oxide takes place in the vapor phase. The conditions were found for suppressing or even eliminating the gas-phase reaction of NO oxidation to NO₂. A procedure for the gas-chromatographic analysis of the reaction products in the catalytic oxidation of ammonia is proposed using several samples and packed columns, including the determination of NO with respect to NO₂ formed in the gas-phase oxidation of NO.