Catalytic oxidation of sulphide ions to elementary sulphur in aqueous solutions over transition metal oxides

The catalytic activity of a wide range of transition metal oxides in oxidation of sulphide ions by air in aqueous medium was studied. Some specific features of the reaction mechanism on some of the studied oxides were considered. The transition metal oxides are promising catalysts for practical application. Some of these oxides will allow the preparation of catalysts possessing activity comparable to that of the cobalt phthalocyanine based catalysts, popular in industrial practice.     

Partial oxidation of n-butane over ceria-promoted nickel/calcium hydroxyapatite

LPG has good infrastructure and is anticipated to be used for production of hydrogen, and n-butane which constitutes a main component of LPG for vehicles. Partial oxidation (POX) of n-butane is investigated in this research by employing ceria-promoted Ni/calcium hydroxyapatite catalysts (Ce _x Ni_2.5/Ca₁₀(OH)₂(PO₄)₆ x=0.1–0.3) which have recently been reported to exhibit good catalytic performance in POX of methane and propane. The experiments were carried out with changing ceria content, O₂/n-C₄H₁₀ ratio and reaction temperature. As the O₂/n-C₄H₁₀ ratio increased up to 2.75, the n-C₄H₁₀ conversion and H₂ yield increased and the selectivity of methane and other hydrocarbons decreased. But with O₂/n-C₄H₁₀=3.0, the n-C₄H₁₀ conversion and H₂ yield decreased. Ce_0.1Ni_2.5/Ca₁₀(OH)₂(PO₄)₆ showed the highest n-C₄H₁₀ conversion and H₂ yield on the whole. In durability tests, higher hydrogen yield and better catalyst stability were obtained with the O₂/n-C₄H₁₀ ratio of 2.75 than with the ratio of 2.5.     

Water-gas shift reaction over nickel hydroxides

Charcoal-supported nickel hydroxides were investigated in the water-gas shift reaction and found to exhibit high catalytic activity. Nickel hydroxide structures of the type ^*-Ni(OH)₂·xH₂O are supposed to be the most probable bearers of the catalytic activity. A redox Ni²⁺Ni³⁺ transition is accomplished in these catalysts.     

Cu掺杂Mn／TiO2催化氧化NO性能研究

采用溶胶凝胶法制备了栽体TiO2,在负栽Mn（Ac）：制备Mn／TiO2时掺杂cu,制备了Mn—Cu／TiO2催化剂。考虑了cu的掺杂量、活性组分负载量、焙烧温度等制备条件对其催化氧化No性能的影响。结果表明,最佳条件下制备的催化剂,在反应温度200℃、空速41000h～、No浓度为300×10-6（书）及O2含量为10％条件下,NO氧化率可迭53．08％,250℃时NO氧化率达到74．76％。在220℃以上时H2O对其影响较小,但其抗硫性能还有待进一步研究提高。     

Catalytic oxidation of nitrogen monoxide over La1−xCexCoO3 perovskites

This paper presents an investigation on the NO oxidation properties of perovskite oxides. La_1−xCe_xCoO₃ (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4) perovskite-type oxides were synthesized through a citrate method and characterized by XRD, BET and XPS. The catalytic activities were enhanced significantly with Ce substitution, and achieved the best when x was 0.2, but decreased at higher x values. The performed characterizations reveal that the adsorbed oxygen on the surface plays an important role in the oxidation of NO into NO₂. The surface compounds after the co-adsorption of NO and O₂ at room temperature, were investigated by DRIFTS and TPD experiments. Three species: the bridging nitrate, the hyponitrites and the monodentate nitrate, were formed on the surface. The order of thermal stabilities was as follows: monodentate > hyponitrite > bridging. Among them, only the monodentate nitrate which decomposed at above 300 °C, would desorb NO₂ into the gas phase. When Ce was added, the temperature of monodentate nitrate desorption became low and the adsorption of the other two species decreased. This might be related to the oxidation state of Co on the surface. Analysis by synthesizing the characterization results and catalytic activity data shows that large amounts of adsorbed oxygen, small amount of inactive compounds on the surface and low NO₂ desorption temperature are favorable for the oxidation of NO.     

A voltammetric study of α- and β-hydroxides over nickel alloys

The hydrogen evolution reaction (HER) is one of the most studied electrochemical process due to the alternative energy conversion and the importance in some chemical process. The search for new electrocatalytic materials lead to investigate metals and alloys with particular characteristics/properties. This paper describes aspects of hydrogen adsorption and Ni-hydroxide formation over nickel alloys (SAF2205, INCONEL625 and MONEL400) utilizing cyclic voltammetry. The SAF2205 (6.4% Ni) alloy present behavior analogue to pure Ni electrodes to hydroxide species, and can bring some advantages to HER compared with the carbon steel (SAE1020) electrode commonly utilized in industrial process.     

Partial oxidation of methane to synthesis gas over iridium–nickel bimetallic catalysts

Partial oxidation of methane to synthesis gas was carried out using supported iridium–nickel bimetallic catalysts, in order to reduce loading levels of iridium and nickel, and to avoid carbon deposition on nickel-based catalysts by adding iridium. The performance of supported iridium–nickel bimetallic catalysts in synthesis gas formation depended strongly upon the support materials. La₂O₃ gave the best performance among the support materials tested. Ir(0.25 wt%)–Ni(0.5 wt%)/La₂O₃ afforded 36% conversion of methane (CH₄/O₂=5) to give CO and H₂ with the selectivities of above 90% at 800°C, and those at 600°C were 25.3% conversion of methane and CO and H₂ selectivities of about 80%, respectively. Reduced monometallic Ir(0.25 wt%)/La₂O₃ and Ni(0.5 wt%)/La₂O₃ catalysts did not produce synthesis gas at 600°C. A higher conversion of methane was obtained by synergistic effects. The product concentrations of CO, H₂, and CO₂, and CH₄ conversion were maintained in high values, even increasing the space velocity of feed gas over Ir–Ni/La₂O₃ catalyst, indicating that rapid reaction takes place. As a by-product, a small amount of carbon deposition was observed, but carbon formation decreased with increasing the space velocity. On the other hand, with reduced monometallic Ni(10 wt%)/La₂O₃ catalyst, yield of synthesis gas and carbon decreased with increasing the space velocity.     

Electrocatalytic oxidation of urea by nanostructured nickel/cobalt hydroxide electrodes

The present paper describes the catalytic oxidation of urea performed by nickel hydroxide and nickel/cobalt hydroxide modified electrodes by using both electrodeposited films and nanoparticles. The incorporation of Co foreign atoms leads to a slight increase in sensitivity besides the shift in redox process, avoiding the oxygen reaction. Nanostructured Ni₈₀Co₂₀(OH)₂ was synthesized by sonochemical route producing 5 nm diameter particles characterized by high-resolution transmission electron microscopy (HRTEM) being immobilized onto electrode by using the electrostatic Layer-by-layer technique, yielding attractive modified electrodes for sensor development.     

超细CuO粉体用于异丙苯氧化反应的研究

近年来,苯酚市场需求增长速率较快,提高苯酚的生产技术及生产能力并降低成本势在必行。以Cu(NO₃)₂·3H₂O和NaOH为原料,采用固相研磨混合法在室温下制备了超细CuO,采用X射线衍射（XRD）和扫描电镜（SEM）对合成CuO的结构和形貌进行了表征分析,并与分析纯的CuO相比较。将超细CuO用于空气氧化异丙苯制过氧化氢异丙苯（CHP）的反应。常压下,考察了反应温度和催化剂用量等条件对CHP浓度的影响,100 mL异丙苯加入1 g催化剂,90 ℃反应12 h后,CHP累积浓度达27%左右,符合工业生产要求。催化剂回收后经简单再生处理可重复使用。     

Effect of nickel oxide synthesis conditions on its physical properties and electrocatalytic oxidation of methanol

Nickel oxide (NiO) was synthesized using several methods and the various physical characteristics observed were correlated to differences in electrocatalytic activity, specifically relating to the oxidation of methanol in alkaline media. Room temperature NaOH-precipitated NiO showed the highest activity and stability towards methanol oxidation in hydroxide (0.005 M KOH) and carbonate (0.1 M Na₂CO₃) media of similar alkalinity. Rapid degradation of NiO electrodes was attributed to microcracking and disintegration associated with the formation of the γ-NiOOH/α-Ni(OH)₂ redox couple, in addition to repeated scans through the oxygen evolution reaction region. Carbonate electrolytes also exhibited average current ranges 3–4 times higher and charge transfer resistances around 85% lower than hydroxide electrolytes. This suggests carbonate may provide a better medium in terms of higher activity and more moderate alkalinity for electrochemical reactions than hydroxide solutions.     

Catalytic oxidation of CO over Ag-Co/alumina catalysts

Low-loading silver cobalt catalysts on alumina for the catalytic oxidation of carbon monoxide were synthesized following different preparation methods: the single-step sol-gel method and the impregnation method. A catalyst synthesized by the single-step sol-gel method gave high surface area values. The activities of alumina-supported silver-cobalt catalysts were studied to obtain the effects of the calcination temperature, metal loading, and preparation methods on CO oxidation at low temperature. The catalysts prepared by impregnation metals on the alumina synthesized by the sol-gel method gave the best activity for the CO oxidation. Catalytic activity conversion of (5 wt% Ag-5 wt% Co)/Al 2 O 3 catalysts prepared by the sol-gel-impregnation method reached 100% at 200°C. Increasing silver loading over the catalysts gave rise to more active catalysts. The sol-gel catalysts had poor activity at low temperature.     

Nickel hydroxide electrocatalysts for alcohol oxidation reactions: An evaluation by infrared spectroscopy and electrochemical methods

We have investigated the electrochemical oxidation of four alcohols (methanol, 1-, 2- and tertiary butanol) at Ni hydroxide electrodes in alkaline electrolytes. In situ FTIR spectroscopy and electrochemical methods have been used to examine these oxidation reactions. Oxidation of the primary and secondary alcohols commences in the potential region where it is proposed that multi-layers of NiOOH are formed on the electrode surface; while no reaction occurs with tertiary butanol. Methanol oxidation occurs in two stages, with predominantly formate being formed in the potential window 0.36-0.44 V (vs. SCE), followed by further oxidation to carbonate at potentials above approx. 0.45 V. Butanoate is the only detected reaction product for 1-butanol electrooxidation in the potential range 0.36-0.5 V. The oxidation of 2-butanol is more complex. In the lower potential range (0.36-0.44 V) the major reaction product is butanone, which is further oxidised at higher potentials to either acetate or a mixture of propanoate and formate (or carbonate). In addition, rate constants have been determined for the first stage of the electrochemical oxidation of all the alcohols investigated.     

Methane partial oxidation to synthesis gas using nickel on calcium aluminate catalysts

Nickel was supported on calcium aluminate carriers that were obtained with varying CaO to Al₂O₃ molar ratios and calcination temperatures. The variations of the supports lead to catalysts of different surface properties and catalytic performance. Metallic nickel (Ni⁰) was proven to be the active species for the methane partial oxidation reaction. The presence of filamentous carbon on used catalysts was also suggested. The differences in the catalytic activity and selectivity for the methane partial oxidation reaction was ascribed to a varying degree of reducibility of the surface nickel species.     

Partial oxidation of methane over nickel-added strontium phosphate

It was found that nickel-added strontium phosphate exhibited high activity and selectivity in partial oxidation of methane. The optimum nickel content could be determined. Over the optimum catalyst, methane conversions and H₂ and CO concentrations in excess of those predicted by the thermodynamic equilibrium were observed. It is believed that the catalytically active species is metallic nickel. This metallic nickel is considered to come from nickel-substituted strontium phosphate under reducing environment, giving highly dispersed nickel metal particles.     

Catalytic oxidation of ethyl acetate over a cesium modified cryptomelane catalyst

Cryptomelane-type manganese oxide was synthesized by redox reaction under acid and reflux conditions. Cesium was incorporated into the tunnel structure by the ion-exchange technique. The catalytic oxidation of ethyl acetate in low concentration (1600 ppmv) was used to test the performance of the catalysts prepared. The presence of small amounts of cesium was found to improve the catalytic performance of cryptomelane. This behaviour was correlated with the basic properties of the catalyst. Temperature programmed experiments, and tests without oxygen in the feed, suggest that lattice oxygen atoms can react with ethyl acetate at low temperatures and are involved in the mechanism of ethyl acetate oxidation.     

Catalytic oxidation of odorous organic acids

Emissions of volatile organic acids is a significant problem in rural communities. So far no one has considered catalytic solutions to the problem but catalytic alternatives look quite reasonable. In this paper we present the results of the first study of the oxidation of a series of odorous organic acids on copper catalysts. We find that the organic acids are easily oxidized on commercial copper on alumina catalysts. Light-off temperatures vary from 180°C for n-butyric acid to 220°C for acetic acid. The rate of oxidation of acetic and i-butyric acid show simple power law dependence on the concentrations of the reactants. In contrast, the oxidation of n-butyric, i-valeric and n-valeric acids show rates which reach a maximum at intermediate oxygen concentrations. Analysis of the data indicates that the copper can exist in two different states: a more active and a less active state.

These results provide the first evidence that catalytic processes are viable for emissions control in rural communities.     

Promotion effects of ceria in partial oxidation of methane over Ni-calcium hydroxyapatite

Effects of ceria added as a promoter to a nickel-calcium hydroxyapatite catalyst, which has recently been reported to exhibit high activity and selectivity in partial oxidation of methane, were investigated. The ceria-promoted catalyst exhibited higher activity and stability than the unpromoted one. This is considered due to the oxygen storage capacity of ceria, which promotes easier removal of the deposited carbon. The optimum content of ceria was determined to lie in the range of the Ce/Ni ratio from 0.1/2.5 to 0.2/2.5.     

Catalytic oxidation of 1,2-dichlorobenzene over ABO3-type perovskites

Several ABO₃-type perovskite oxides (A = La, Y, Nd or Gd; B = Fe, Mn, Cr or Co) have been investigated as catalysts for the oxidation of 1,2-dichlorobenzene (o-DCB), a model compound for the highly toxic polychlorinated dibenzodioxins. Initial transient and steady state activity measurements were conducted with all catalysts in the absence and presence of water. Perovskites containing Cr in the B-site were more active than perovskites containing other transition metals, with YCrO₃ being the most active catalyst among the different systems studied. Furthermore, YCrO₃ did not show any loss of its initial activity after several hours on stream. Other perovskites lost 10–20% of their initial activity within the first 5–10 h on stream. This loss was associated with a corresponding loss in BET surface area. With the exception of LaCoO₃, all perovskites retained their crystalline structure upon exposure to o-DCB under reaction conditions. LaCoO₃ was converted to LaOCl and Co₃O₄. The presence of water appeared to enhance the catalytic activity of some perovskites. This effect can be attributed to a faster removal of Cl⁻ ions from the catalyst surface via their reaction with water.     

Electrocatalytic oxidation of methanol on carbon paste electrode modified by nickel ions dispersed into poly (1,5-diaminonaphthalene) film

Poly (1,5-diaminonaphthalene) film was prepared by using the repeated potential cycling technique in an acidic solution at the surface of carbon paste electrode. Then transition metal ions of Ni(II) were incorporated to the polymer by immersion of the modified electrode in a 1.0 M nickel chloride solution. The electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)/Ni(II) couple. Also, cyclic voltammetric experiments showed that methanol electrooxidized at the surface of this Ni(II) dispersed polymeric modified carbon paste electrode [Ni/P-1,5-DAN/MCPE]. The mechanism of methanol oxidation changes from diffusion control at low concentration to a catalytic reaction at higher methanol concentration. The effects of both scan rate and methanol concentration on the anodic peak height of the methanol oxidation were discussed.