Acetone oxidation using ozone on manganese oxide catalysts

Supported manganese oxide catalysts were prepared by the impregnation of alumina foam blocks washcoated with alumina and silica. The manganese content based on the weight of the washcoats was 10 wt % calculated as MnO2. Fourier transform profiles of the Mn K-edge EXAFS spectra for these samples gave three distinctive peaks at 0.15, 0.25, and 0.32 nm and were close to the profiles of Mn3O4 and beta-MnO2. The number of surface active sites was determined through oxygen chemisorption measurements at a reduction temperature (Tred = 443 K) obtained from temperature-programmed reduction (TPR) experiments. Acetone catalytic oxidation was studied from room temperature to 573 K, and was found to be highly accelerated by the use of ozone on both catalysts with substantial reductions in the reaction temperature. The only carbon-containing product detected was CO2. The alumina-supported catalyst was found to be more active than the silica-supported catalyst in acetone and ozone conversion, with higher turnover frequencies (TOFs) for both reactions. The pressure drop through the foam was low and increased little (0.003 kPa/10 000 h(-1)) with space velocity. In situ steady-state Raman spectroscopy measurements during the acetone catalytic oxidation reaction showed the presence of an adsorbed acetone species with a C-H bond at 2930 cm(-1) and a peroxide species derived from ozone with an O-O bond at 890 cm(-1).     

Investigation of H2S oxidation by oxygen on oxide catalysts in sulfur condensation conditions

H₂S oxidation with oxygen has been studied on three industrial oxide catalysts (Fe−Cr−Zn, Cu−Cr−Al, V−Ti−Al). Thermodynamically possible changes in the composition of the catalysts have been evaluated. Regularities determining deep or partial oxidation of H₂S have been found. Deep oxidation is connected to the presence of active oxygen on the catalyst surface; its removal results in a decrease of activity and increase of the sulfur selectivity. Oscillations caused by periodic adsorption-desorption of sulfur on the catalyst surface have been observed on the most active V−Ti−Al catalysts in oxygen excess.     

Effect of potassium on alumina supported chromium oxide catalysts for methylene chloride oxidation

Alumina supported chromium oxide catalysts added potassium were prepared and tested for methylene chloride oxidation. They were investigated by XRD, BET, XPS, chemisorption. Chromium oxide catalyst added potassium of 1 wt.% has a large beneficial effect on activity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Oxidation of ethanol on platinum/alumina and copper oxide catalysts

The oxidation of ethanol on CuO, CuO/Al₂O₃ and Pt/Al₂O₃ catalysts has been studied at various concentrations of alcohol, oxygen and water vapor in the reaction mixture. The reaction order and activation energies have been determined for both complete and partial oxidation processes. A consecutive oxidation scheme is suggested.

---

CuO, CuO/Al₂O₃ Pt/Al₂O₃ , . . .

     

Structure and oxidation state of silica-supported manganese oxide catalysts and reactivity for acetone oxidation with ozone

Silica-supported manganese oxide catalysts with loadings of 3, 10, 15, and 20 wt % (as MnO2) were characterized with use of X-ray absorption spectroscopy and X-ray diffraction (XRD). The edge positions in the X-ray absorption spectra indicated that the oxidation state for the manganese decreased with increasing metal oxide loading from a value close to that of Mn2O3 (+3) to a value close to that of Mn3O4 (+2(2)/3). The XRD was consistent with these results as the diffractograms for the supported catalysts of higher manganese oxide loading matched those of a Mn3O4 reference. The reactivity of the silica-supported manganese oxide catalysts in acetone oxidation with ozone as an oxidant was studied over the temperature range of 300 to 600 K. Both oxygen and ozone produced mainly CO2 as the product of oxidation, but in the case of ozone the reaction temperature and activation energy were significantly reduced. The effect of metal oxide loading was investigated, and the activity for acetone oxidation was greater for a 10 wt % MnOx/SiO2 catalyst sample compared to a 3 wt % MnOx/SiO2 sample.     

Effects of carrier and Mn loading on supported manganese oxide catalysts for catalytic combustion of methane

Supported manganese oxide catalysts were prepared by incipient wetness impregnation method for methane catalytic combustion, and effects of the support （Al2O3, SiO2 and TiO2） and Mn loading were investigated. These catalysts were characterized with N2 adsorption, X-ray diffraction, X-ray photoelectron spectroscopy and temperature-programmed reduction techniques. Methane conversion varied in a large range depending on supports or Mn loading. Al2O3 supported 15% Mn catalyst exhibited better activity toward methane catalytic oxidation. The manganese state and oxygen species played an important role in the catalytic performance,     

Selective oxidation of hydrogen sulfide over potassium promoted vanadium oxide on a alumina catalysts

The effect of potassium addition to alumina supported vanadium catalysts on the catalytic activity for the selective oxidation of H₂S is investigated. XRD, XPS and XANES have been used to characterize a series of K-V/Al₂O₃catalysts. The enhanced sulphur yield has been correlated with the crystallinity of vanadium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cu-Co-Fe oxide catalysts supported on carbon nanotubes for the oxidation of CO

The catalytic activity and adsorption characteristics of the surface of catalysts in the form of carbon nanotubes produced on nickel and cobalt oxides with the Cu-Co-Fe oxide system as supported active phase were studied. At carbon nanotubes produced on nickel oxide with (10 + 10) wt.% of the catalytically active phase total conversion of CO to CO₂ is realized at 47 °C. This sample has high specific surface area and a large volume of mesopores. It was shown that the increase in catalytic activity correlates with the increase in the amount of the α₂ form of CO₂. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 4, pp. 222–226, July–August, 2006.     

Cobalt promoted copper manganese oxide catalysts for ambient temperature carbon monoxide oxidation

Low levels of cobalt doping (1 wt%) of copper manganese oxide enhances its activity for carbon monoxide oxidation under ambient conditions and the doped catalyst can display higher activity than current commercial catalysts.     

Structural thermal and textural studies on cobalt oxide/alumina supported catalysts

CoO/Al₂O₃ catalysts containing amounts of cobalt ranging form 2 to 20% were prepared atpH 11 from neutral mesoporous alumina composed of γ-Al₂O₃ and poorly crystalline boehmite, and were then dried at 80?C. X-ray diffraction, DTA and TG techniques were used to study the structural changes produced upon thermal treatment up to 700?C. Soaking of the alumina in cobalt ammine complex solutions for a period of 10 days (the time required for equilibrium) resulted in a series of catalyst samples (I–V). Another sample (III-a) was soaked for a period of 5 days only in order to study the effect of the soaking time upon the equilibrium conditions. Cobalt aluminate (CoAl₂O₄) bands were characterized in all catalyst samples except III-a. They increased in intensity with increasing cobalt content. Surface species appeared in samples heated to 80?C, and others persisted at 150?C. Heating to temperatures above 200?C resulted in the formation of cobalt oxides, due to decomposition of the surface compounds. DTA and TG studies showed that this was more pronounced at higher concentrations of cobalt. Samples heated at 500?C and above did not undergo any further structural changes, except that the boehmite in the support was converted to γ-Al₂O₃. The variations in the surface parameters followed the same pattern as found previously [1], demonstrating that the catalyst samples are mesoporous, with retention of two ranges of pore size in most cases.     

Au/TiO2催化剂上非催化CO氧化反应中活性氧物种的生成和消除

在定量的瞬时产物分析(TAP)反应器中,于80 oC下采用CO脉冲和O2脉冲补充等方法,研究了高温(400 oC)焙烧的Au/TiO2催化剂上活性氧物种的移除反应活性,特别是活性氧物种的性质。以往的研究大多关注的是CO催化氧化反应中活性氧物种及其性质,在典型的反应条件下该物种的形成和消除是可逆的;而本研究表明,催化剂直接焙烧后就存在额外的氧物种;该物种对CO氧化反应也具有活性,但其在典型的反应条件下不生成或生成很少。基于此,讨论了Au/TiO2催化剂上CO氧化反应的机理,特别是不同活性氧物种的作用。     

Thermally stable multicomponent manganese catalyst for the deep oxidation of methane to CO2

A thermally stable manganese oxide catalyst for the deep oxidation of lean CH₄ mixtures with air to CO₂ was developed and characterized. To prepare this catalyst, new approaches to the synthesis of polyoxide catalysts based on Mn modified with La, Ce, Ba, and Sr by supporting them from nitrate solutions onto alumina granules stabilized with 2% Ce were used. The catalyst gave the degree of CH₄ oxidation to CO₂ at a level of 90–98% at a CH₄ concentration of 0.2–4.0% in air (space velocity of 10 × 10³ h^?1; temperature of 973 K). The heating of a Mn-containing sample in air to 1373 K had no negative effect on the conversion of CH₄; an insignificant decrease in the catalyst activity (by ～10%) was observed only on heating above 1473 K. The degree of CH₄ oxidation to CO₂ depended only slightly on O₂ and CH₄ concentrations varied over the ranges 2–20 and 0.5–4.0%, respectively. With the use of physicochemical techniques (XRD analysis, BET, electronic diffuse-reflectance spectroscopy, TPD, TPR, and TPO), it was found that the catalyst underwent considerable phase transformations as the temperature was increased to 1473 K: Mn₂O₃ clusters, which occurred at 873 K, were partially converted into LaMnO₃ perovskites above 1173 K or LaMnAl₁₁O₁₉ hexaaluminates above 1273 K. Oxygen that is the constituent of the latter species participated in the oxidation of CH₄ to CO₂.     

Redox processes in o-xylene oxidation over V?Ti oxide catalysts

It has been established that fast relaxations are due to catalytic conversion and slow ones are due to the formation of structures with decreasing activity and selectivity.

---

, , — , .

     

CO oxidation on Aun/TiO2 catalysts produced by size-selected cluster deposition

Planar model catalysts were prepared by deposition of size-selected gold clusters containing up to seven atoms on rutile TiO2 (110). Molecular oxygen is observed to bind inefficiently to the surface, probably at oxygen vacancies, and some oxygen also appears to bind to the gold clusters. Stable CO binding is observed atop gold for catalysts prepared by Au and Au2 deposition, but not for larger Aun. CO oxidation activity is strongly dependent on cluster size, with Au7-prepared samples >50 times more reactive than samples prepared by Au or Au2 deposition     

Selective oxidation of methane to formaldehyde by oxygen over silica-supported iron catalysts (Special column of methane transformation, Article)

FeO_x-SiO₂ catalysts prepared by a sol-gel method were studied for the selective oxidation of methane by oxygen. A single-pass formaldehyde yield of 2.0% was obtained over the FeO_x-SiO₂ with an iron content of 0.5 wt% at 898 K. This 0.5 wt% FeO_x-SiO₂ catalyst demonstrated significantly higher catalytic performances than the 0.5 wt% FeO_x/SiO₂ prepared by an impregnation method. The correlation between the catalytic performances and the characterizations with UV-Vis and H₂-TPR suggested that the higher dispersion of iron species in the catalyst prepared by the sol-gel method was responsible for its higher catalytic activity for formaldehyde formation. The modification of the FeO_x-SiO₂ by phosphorus enhanced the formaldehyde selectivity, and a single-pass formaldehyde yield of 2.4% could be attained over a P-FeO_x-SiO₂ catalyst (P/Fe = 0.5) at 898 K. Raman spectroscopic measurements indicated the formation of FePO₄ nanoclusters in this catalyst, which were more selective toward formaldehyde formation.     

Effect of cerium oxide on the activity of platinum catalysts of hydrogen and CO oxidation

Effective catalytic systems based on Pt/CeO₂-C were prepared. The use of a cerium oxide addition in the substrate stabilized the platinum catalysts against their poisoning with carbon monoxide at room temperature.