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Laura E. Briand

Bio: Laura E. Briand is an academic researcher from National University of La Plata. The author has contributed to research in topics: Catalysis & Methanol. The author has an hindex of 23, co-authored 61 publications receiving 1965 citations. Previous affiliations of Laura E. Briand include Ruhr University Bochum & Lehigh University.
Topics: Catalysis, Methanol, Oxide, Vanadium, Adsorption


Papers
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TL;DR: In this article, the molecular structures and reactivity of the group V metal oxides (V 2 O 5, Nb 2 O5 and Ta 2 o 5 ) were compared.

264 citations

Journal ArticleDOI
TL;DR: In this article, the authors summarized the literature concerning the structure, hydrolytic stability in solution, thermal stability in the solid state, redox-acid properties and applications of heteropoly-compounds with Wells-Dawson structure.
Abstract: The scientific literature concerning the structure, hydrolytic stability in solution, thermal stability in the solid state, redox-acid properties and applications of heteropoly-compounds (HPCs) with Wells–Dawson structure is summarized in the present work. Wells–Dawson heteropoly-anions possess the formula [(X n+ )2M18O62] (16−2n)− where X n+ represents a central atom (phosphorous(V), arsenic(V), sulfur(VI), fluorine) surrounded by a cage of M addenda atoms, such as tungsten(VI), molybdenum(VI) or a mixture of elements, each of them composing MO6 (M-oxygen) octahedral units. The addenda atoms are partially substituted by other elements, such as vanadium, transition metals, lanthanides, halogens and inorganic radicals. The Wells–Dawson heteropoly-anion is associated with inorganic (H + , alkaline elements, etc.) or organic countercations forming hybrid compounds. Wells–Dawson acids (phospho-tungstic H6P2W18O62·24H2O, phospho-molybdic H6P2Mo18O62·nH2O and arsenicmolybdic H6As2Mo18O62·nH2O) possess super-acidity and a remarkably stability both in solution and in the solid state. These properties make them suitable catalytic materials in homogeneous and heterogeneous liquid-phase reactions replacing the conventional liquid acids (HF, HCl, H2SO4, etc.). Although, the application of the acids in heterogeneous gas-phase reactions is less developed, there is a patented method to oxidize alkanes to carboxylic acids on a supported Wells–Dawson catalyst that combines acid and redox properties. Wells–Dawson anions possess the ability to accept or release electrons through an external potential or upon exposure to visible and UV radiation (electro and photochemical reactions). Additionally, Wells–Dawson HPCs catalyze the oxidation of organic molecules with molecular oxygen, hydrogen peroxide and iodosylarenes; epoxidation and hydrogenation in homogeneous and heterogeneous liquid-phase conditions. The ability of transition metal substituted Wells–Dawson HPCs to be reduced and re-oxidized without degradation of the structure is promising in the application of those HPCs replacing metalloporphyrins catalysts in redox and electrochemical reactions.

184 citations

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TL;DR: It was demonstrated that there is no sample damage by the more energetic UV excitation when very low laser powers and fast detectors are employed, thus avoiding the need of complicated fluidized bed sample arrangements sometimes used for UV Raman investigations.
Abstract: The visible (532 and 442 nm) and UV (325 nm) Raman spectra of bulk mixed metal oxides (metal molybdates and metal vanadates) were compared on the same spectrometer, for the first time, to allow examination of how varying the excitation energy from visible to UV affects the resulting Raman spectra. The quality of the Raman spectra was found to be a strong function of the absorption properties of the bulk mixed oxide. For bulk mixed metal oxides that absorb weakly in the visible and UV regions, both the visible and UV Raman spectra were of high quality and exhibit identical vibrational bands, but with slightly different relative intensities. For bulk mixed metal oxides that absorb strongly in the UV and visible regions and/or strongly in the UV and weakly in the visible regions, the visible Raman spectra are much richer in structural information and of higher resolution than the corresponding UV Raman spectra. This is a consequence of the strong UV absorption that significantly reduces the sampling volume and number of scatterers giving rise to the Raman signal. The shallower escape depth of UV Raman, however, was not sufficient to detect vibrations from the surface metal oxide species that are present on the outermost surface layer of these crystalline mixed metal oxide phases as previously suggested. It was also demonstrated that there is no sample damage by the more energetic UV excitation when very low laser powers and fast detectors are employed, thus avoiding the need of complicated fluidized bed sample arrangements sometimes used for UV Raman investigations. The current comparative Raman investigation carefully documents, for the first time, the advantages and disadvantages of applying different excitation energies in collecting Raman spectra of bulk mixed metal oxide materials.

136 citations

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TL;DR: The Wells-Dawson acid was used as a catalyst for producing methyl tert-butyl ether (MTBE) from methanol and isobutylene in the gas phase at 373 K.
Abstract: The Wells–Dawson acid was studied as a catalyst for producing methyl tert-butyl ether (MTBE) from methanol and isobutylene in the gas phase at 373 K. Thus, pure Wells–Dawson acid was synthesized and characterized by 31 P NMR, XRD, FTIR and TGA-DTA measurements. The results indicated that the Dawson acid keeps its heteropolyoxoanion structure up to 873 K. The samples were active and very selective (close to 100%) for MTBE production and showed stable behavior during the reaction period of 3 h. The conversion observed on reference catalyst Amberlyst 15-wet under the same conditions was significantly lower. The acid was also tested in methanol dehydration to dimethyl ether at 373 K. For both reactions, the catalytic activity depends on the pretreatment temperature of the acid. The activity was approximately constant up to 473 K; then activity decreased steadily until becoming null when pretreatment temperature was 673 K. The catalytic results were explained using the pseudoliquid phase behavior concept.

112 citations


Cited by
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TL;DR: In this article, a comparison of the molecular structure and reactivity information of supported vanadium oxide catalysts is presented, which provides new fundamental insights into the catalytic properties of surface vanadia species during hydrocarbon oxidation reactions.
Abstract: Supported vanadium oxide catalysts, containing surface vanadia species on oxide supports, are extensively employed as catalysts for many hydrocarbon oxidation reactions. This paper discusses the current fundamental information available about the structure and reactivity of surface vanadia species on oxide supports: monolayer surface coverage, stability of the surface vanadia monolayer, oxidation state of the surface vanadia species, molecular structures of the surface vanadia species (as a function of environment and catalyst composition), acidity of the surface vanadia species and reactivity of the surface vanadia species. Comparison of the molecular structure and reactivity information provides new fundamental insights into the catalytic properties of surface vanadia species during hydrocarbon oxidation reactions: (1) the role of terminal VO, bridging VOV and bridging VO-support bonds, (2) the number of surface vanadia sites required, (3) the influence of metal oxide additives, (4) the influence of surface acidic and basic sites, (5) the influence of preparation methods and (6) the influence of the specific oxide support phase. The unique physical and chemical characteristics of supported vanadia catalysts, compared to other supported metal oxide catalysts, for hydrocarbon oxidation reactions are also discussed.

644 citations

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TL;DR: A general overview of the characteristics and properties of the materials applied for enzyme immobilization can be found in this article, where support materials are divided into two main groups, called Classic and New materials.
Abstract: In recent years, enzyme immobilization has been presented as a powerful tool for the improvement of enzyme properties such as stability and reusability. However, the type of support material used plays a crucial role in the immobilization process due to the strong effect of these materials on the properties of the produced catalytic system. A large variety of inorganic and organic as well as hybrid and composite materials may be used as stable and efficient supports for biocatalysts. This review provides a general overview of the characteristics and properties of the materials applied for enzyme immobilization. For the purposes of this literature study, support materials are divided into two main groups, called Classic and New materials. The review will be useful in selection of appropriate support materials with tailored properties for the production of highly effective biocatalytic systems for use in various processes.

580 citations