Complex Oxide Catalysts Research Articles

Environmental high resolution electron microscopy and applications to chemical science

An environmental cell high resolution electron microscope (EHREM) has been developed for in situ studies of dynamic chemical reactions on the atomic scale. It allows access to metastable intermediate phases of catalysts and to sequences of reversible microstructural and chemical development associated with the activation, deactivation and poisoning of a catalyst. Materials transported through air can be restored or recreated and samples damaged, e.g. by dehydration, by the usual vacuum environment in a conventional electron microscope can be preserved. A Philips CM30 HRTEM/STEM system has been extensively modified in our laboratory to add facilities for in situ gas-solid reaction studies in controlled atmospheres of gas or vapor at pressures of 0–50 mbar, instead of the regular TEM high vacuum environment. The integrated new environmental cell capability is combined with the original 0.23 nm TEM resolution, STEM imaging (bright field/annular dark field) and chemical and crystallographic microanalyses. Regular sample holders are used and include hot stages to > 1000°C. Examples of applications include direct studies of dynamic reactions with supported metal particle catalysts, the generation of defects and structural changes in practical complex oxide catalyst systems under operating conditions and carbon microstructures.

X-Ray Characterization of Complex Oxide Catalysts under Preparation and Reaction Conditions: Catalysts for Methanol Synthesis

X-Ray Characterization of Complex Oxide Catalysts under Preparation and Reaction Conditions: Catalysts for Methanol Synthesis

Iron-Aluminum Cluster Catalysts Obtained by Alkoxy Synthesis .: 1. Liquid-Phase Oxidation of Hexadecane

Iron-substituted boehmite gel has been prepared by alkoxy synthesis, i.e., by reaction of Fe(acac)3 with a fresh surface of AlOOH. Iron-aluminum complex oxide catalysts for liquid-phase oxidation of hexadecane were prepared by annealing the gel precursors. The gels with 0-20 wt.% of iron loading were studied by magnetic susceptibility and Mössbauer spectroscopy. Depending on the iron concentration, differing amounts of paramagnetic Fe3+ ions in the boehmite structure and small ferrimagnetic spinel clusters were observed in the X-ray amorphous precursors. Thermal treatment led to formation of substituted spinels, FexAl2−xO3, as well as γ-ferric oxide clusters. The overall rate of hexadecane oxidation increased with an increase in the relative content of magnetic clusters. The inclusion of nonmagnetic Al3+ ions in the γ-Fe2O3 lattice reduced the number of terminal Fe3+ O groups and the overall catalytic activity. The role of electronically excited terminal oxygen on the surface of γ-ferric oxide clusters in the mechanism of hexadecane oxidation is discussed.

Vapour phase oxidation of benzoic acid to phenol over NiO–Fe2O3catalysts

The NiO–Fe2O3 complex oxide catalysts, which were prepared by precipitation and then calcined at around 800 °C, showed excellent catalytic activity in the vapour phase oxidation of benzoic acid to selectively form phenol.

Synthesis and characterisation of porous polymers

AbstractState‐of‐the‐art electron microscopic studies have been made of the ultrastructure of a matrix of specifically prepared styrene‐divinylbenzene resin sorbents. Image analysis methods have been applied to quantify the porous morphology of these resins in the “dry”, “freeze‐dried” and “frozen” states. Significant swelling has been demonstrated in the wet state. Highly porous Polyhipe® monoliths have been prepared and used to produce a polyamide‐impregnated composite support for use in solid phase synthesis of peptides. The composite shows good pressure resistance and allows high yields of pure peptides to be achieved. Polyhipe® polymers with very high surface areas (up to 350 m2g−1) have been prepared by applying the methodologies of porous particulate resin production to achieve highly porous walls in the Polyhipe® structures. Finally, novel procedures are described for the preparation of porous particulate polyimides and polybenzimidazoles involving a paraffin oil dispersion methodology. These thermooxidatively stable resins have been prepared with modest surface areas of ∼30 m2g−1 and offer good prospects for use as supports for alkene transition metal complex oxidation catalysts.

Magnetism and catalytic oxidation action of RSrMnO

A series of complex oxide catalysts R 0.7Sr 0.3MnO 3 are investigated (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er). All samples are paramagnetic except LaSrMnO which displays a small hysteresis loop. The susceptibilities of the samples containing the light rare-earth elements (Ce-Gd) are smaller than 1.1×10 -4 emu/g Oe except NdSrMnO, while the susceptibilities of those containing the heavy rare-earth elements exceed 1.2×10 -4 emu/g Oe. Furthermore it is demonstrated that the catalysis of these samples in oxidation of CO have been inproved with the existence of a magnetic field at 200°C, especially for R = Nd, Gd and Tb.

Mössbauer study of the methane oxidative coupling catalysts with K2NiF4 layer structure

Six complex oxide catalysts with K2NiF4-type structure were prepared by solid state reaction for methane oxidative coupling (MOC). Mossbauer spectroscopy and other methods were used to identify the structure of the samples and the electronic configuration of iron atoms, and the results were correlated with the MOC reactivity. It is found that the partial substitution of iron in the lattice by Li, Zn or Mg results in the formation of high spin Fe(IV) and surface oxygen species O−, which are assumed to be responsible for the high activity and C2 selectivity for MOC.

Catalytic (amm)oxidation of propane with molecular oxygen over complex metal oxides: Involvement of homogeneous reaction in gas phase

Partial oxidation of propane to acrolein and ammoxidafion to acrylonitrile with molecular oxygen proceed over complex metal oxide catalysts under the restricted conditions of the high partial pressures of both propane and oxygen. The selective formations of acrolein and acrylonitrile also required high reaction temperature around 500°C. Effective catalysts for the selective (amm)oxidation were mostly made up of bismuth oxide and molybdenum oxide and were further modified with another metal oxide. From the studies of the volume effect of pre-catalyst zone on the conversion and the selectivities and of the reactions in the absence of the catalyst, it is suggested that the reactions involve homogeneous reactions in the gas phase where thermally activated propane converts into propene, followed by catalytic oxidation of propene over the metal oxide surface.

Oxidative dehydrodimerization of methane over complex oxide catalysts prepared by self-propagating high-temperature synthesis

Oxidative dehydrodimerization of methane to C 2 - hydrocarbons has been examined for complex oxide ceramics prepared by using method of self-propagating high-temperature synthesis (SHS) in a combustion mode. The novel catalysts containing rare-earth, alkali-earth metals and copper showed sufficiently high level of activity, C 2 selectivity and stability in the presence of oxygen at temperature 700–800C, atmospheric pressure, the mole ratio CH 4/O 2= 5–8 and contact time 0.6–9.0 s.

ChemInform Abstract: Polymer‐Supported Metal Complex Oxidation Catalysts

ChemInformVolume 19, Issue 30 Reviews ChemInform Abstract: Polymer-Supported Metal Complex Oxidation Catalysts D. C. SHERRINGTON, D. C. SHERRINGTON Dep. Pure Appl. Chem., Univ. Strathclyde, Glasgow G1 1XL, ScotlandSearch for more papers by this author D. C. SHERRINGTON, D. C. SHERRINGTON Dep. Pure Appl. Chem., Univ. Strathclyde, Glasgow G1 1XL, ScotlandSearch for more papers by this author First published: July 26, 1988 https://doi.org/10.1002/chin.198830369Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue30July 26, 1988 RelatedInformation

Polymer-supported metal complex oxidation catalysts

Abstract

Acio-Base properties and actvity of complex oxide catalysts for m-xylene ammoxidation

Introduction of small quantities of alkaline and alkalineearth metal oxides into supported Sb−Bi−V oxide catalysts increasses the concentration of surface basic centers and increases significantly its activity in m-xylene ammoxidation. Promoting effect is suggested to be due to the heterolytic type of the primary activation of hydrocarbon.

The Wet Oxidation of Organic Compounds Catalyzed by Co–Bi Complex Oxide

Abstract The wet oxidation of various organic compounds was carried out in the presence of the Co–Bi (5:1) complex oxide catalyst. The catalyst was especially effective for the oxidation of all refractory lower carboxylic acids, which are intermediates in the wet oxidation of many organic compounds.

Catalytic properties and phase composition of multicomponent catalysts for oxidative ammonolysis of propane

Studies of the phase composition and catalytic properties of several complex oxide catalysts for oxidative ammonolysis of propane indicate that the active phases of these catalysts are antimonates of the respective metals. Phosphorus and tungsten additives to the catalysts promote the formation of such phase compositions, i.e. the formation of antimonates and the binding of excess antimony oxide.

Modification of a magnesium—Molybdenum olefin oxidation catalyst by alkali additives

The effect of alkali elements incorporated into a magnesium-molybdenum system containing iron and bismuth ions on the structure and catalytic activity in isobutylene oxidation to methylacrolein was studied. It was found by Mössbauer spectroscopy and EPR that potassium and cesium ions are capable of rearranging the iron molybdate structure to form a substituted garnet, whereas the lithium and sodium ions exhibit no such effect. The iron ions were found to interact in the modified system. Comparison of data on structure with the catalysis results revealed that the structural rearrangement of iron molybdate in a complex oxide catalyst increases the process selectivity, due to changes in the lattice oxygen state.

The study of selective oxidation of propylene on complex oxides by means of temperature-programmed desorption

The interaction of propylene with a number of complex oxide catalysts has been investigated by means of thermal desorption. The results indicate that propylene is adsorbed on only one type of active site and that this site is energetically similar for all the selective oxidation catalysts tested. The adsorbed propylene can react at the site to form acrolein via two different mechanisms. One of the mechanisms involves lattice oxygen, and the other, adsorbed oxygen, but in both cases the acrolein is derived from a common hydrocarbon intermediate. On one catalyst, a modified cobalt molybdate, evidence is given which shows that the rate-determining step in the selective oxidation of propylene is the desorption of acrolein and not the surface reaction.

The ammoxidation of propene over complex oxide catalysts

The ammoxidation of propene over complex oxide catalysts

Effect of chemical composition and of methods of preparation on physico-chemical properties of complex oxide catalysts: Silica-magnesia catalysts

Effect of chemical composition and of methods of preparation on physico-chemical properties of complex oxide catalysts: Silica-magnesia catalysts

Effect of chemical composition and methods of preparation of complex oxide catalysts upon their physico-chemical and catalytic properties: Alumino-silicate catalysts

Effect of chemical composition and methods of preparation of complex oxide catalysts upon their physico-chemical and catalytic properties: Alumino-silicate catalysts

Effect of chemical composition and methods of preparation of complex oxide catalysts upon their physico-chemical and catalytic properties: Silica-zirconia catalysts

The average blood lead concentration has significantly decreased over the last two decades among the general population. However, in Belgium, there are still high-risk populations such as groups of pregnant women who have shown elevated lead levels. The objective of this study was to evaluate the current situation of lead cord blood levels and identify sources of lead exposure by a questionnaire survey. The study was conducted in 5 maternity units in Belgium; for each, umbilical cord blood samples were collected from 50 consecutive births. At the same time a questionnaire on possible sources of lead exposure was administered to the mother. The dependant variable was a dichotomous lead level variable (<20 μg/L vs. ≥20 μg/L). The factors associated with elevated lead levels (≥20 μg/L) were mother's country of origin from south Mediterranean and from Sub-Saharan Africa, mother's educational level, using ‘tagine’ plates for cooking and using khol for make-up, but, after adjusting for potential confounding factors, only the mother's country origin from south Mediterranean (adjusted odds ratio, 5.51; 95% confidence interval [CI], 1.68–18.08; p = 0.005) and from Sub-Saharan Africa (adjusted odds ratio, 8.14; 95% CI, 2.26–29.40; p = 0.001) were significantly associated with elevated cord blood lead concentrations (≥20 μg/L). The results of this study are similar to those found by a previous study in Belgium in 2004. Sources of exposure are difficult to distinguish with this questionnaire, which might be due to other important sources of exposure that were not included in the questionnaire. Confirmation of these risk factors in future studies could lead to new prevention strategies for populations who are at risk for subsequent lead exposure.