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Toshio Okuhara - One of the best experts on this subject based on the ideXlab platform.

  • mesostructured vanadium Phosphorus Oxides assembled with exfoliated vopo4 nanosheets
    Microporous and Mesoporous Materials, 2005
    Co-Authors: Yuichi Kamiya, Naoki Yamamoto, Hiroyuki Imai, Shinichi Komai, Toshio Okuhara
    Abstract:

    Abstract Hexagonal- and lamellar-mesostructured vanadium Phosphorus Oxides were synthesized by assembling exfoliated VOPO 4 sheets using cationic surfactants (dodecyl-, tetradecyl-, hexadecyl-, and octadecyltrimethylammonium bromide, C n TAB). The products were characterized using X-ray diffraction, SEM, TEM, IR spectroscopy, elemental analysis, and TG/DTA. When a suspension of VOPO 4  · 2H 2 O crystallites in 2-propanol was thermally treated, 2-propanol intercalated between layers of VOPO 4  · 2H 2 O, followed by exfoliation of the layers. C n TAB was added to the alcoholic solution at 343 K. Treatment of the solution at 343 K for 10 min, followed by evaporation of 2-propanol, which resulted in the formation of hexagonal- and lamellar-phases at C n TAB/VOPO 4 molar ratios of 0.5, and 1.0, respectively, with chemical formulae of [C 16 H 33 N(CH 3 ) 3 Br] 0.5 (VOPO 4 ) · 0.4H 2 O and [C 16 H 33 N(CH 3 ) 3 Br] 1.0 (VOPO 4 ), respectively. The unit cell constants of hexagonal- and lamellar-phases from C 16 TAB were a  = 3.86 nm and c  = 3.87 nm, respectively, and increased with carbon number of the primary chain of C n TAB. In the lamellar phases, the surfactant was incorporated as a double layer at an angle of approximately 27° and its wall consisted of two VOPO 4 sheets.

  • highly porous vanadium Phosphorus Oxides derived from vanadyl n butylphosphate
    Microporous and Mesoporous Materials, 2002
    Co-Authors: Yuichi Kamiya, Eiichiro Nishikawa, Atsushi Satsuma, Miki Yoshimune, Toshio Okuhara
    Abstract:

    Abstract Highly porous vanadium Phosphorus Oxides (V–P Oxides) of high specific surface area were synthesized by thermal treatment of layered vanadyl n -butylphosphate in N 2 . The surface area of V–P Oxides was greatly increased by thermal treatment within a temperature range of 500–550 K, and reached 225 m 2  g −1 after treatment at 568 K. The N 2 adsorption–desorption isotherm of V–P oxide is a Type IV isotherm, indicating that this material is mesoporous. Micropore and mesopore size distributions were determined from Saito–Foley analysis using an Ar adsorption isotherm and Dollimore–Heal analysis using an N 2 desorption isotherm, respectively. The pores show a bimodal distribution in the micropore and mesopore region, and the micropores show a broad distribution with small volume (0.004 cm 3  g −1 ). The mesopores, which have a size of 4.4 nm and a volume of 0.272 cm 3  g −1 , were probably formed from fractures of microcrystallites along layers of vanadyl n -butylphosphate.

  • Reaction of layered vanadium Phosphorus Oxides, VOPO4·2H2O and VOHPO4·0.5H2O, with amines and formation of exfoliative intercalation compounds
    Journal of Materials Chemistry, 2000
    Co-Authors: Teruyuki Nakato, Yoko Furumi, Naoshi Terao, Toshio Okuhara
    Abstract:

    Reactions of layered vanadium Phosphorus Oxides, VOPO4·2H2O and VOHPO4·0.5H2O, with aliphatic and aromatic amines were investigated with regard to the formation of intercalation compounds. VOPO4·2H2O was intercalated with 4-butylaniline, and the obtained intercalation compound was exfoliated by stirring in THF. The layered structure of the intercalation compound was reconstructed by removal of the solvent from the suspension of exfoliated solid, while ordering of the restacked layers was sensitive to the experimental conditions. The reactions with 4-butylaniline for prolonged periods caused partial collapse of the layered structure, indicating metastability of the intercalated structure. VOPO4·2H2O formed intercalation compounds with aniline and 4-anilinoaniline as well as 4-butylaniline. On the other hand, reactions with n-alkylamines, which are more basic than aromatic amines, brought about collapse of the layered structure of VOPO4·2H2O. In addition, VOHPO4·0.5H2O did not react with aromatic amines such as aniline and pyridine, while reactions with n-alkylamines did not give intercalation compounds but led to the formation of salts, where the structure of the host lattice was not retained.

  • reaction of layered vanadium Phosphorus Oxides vopo4 2h2o and vohpo4 0 5h2o with amines and formation of exfoliative intercalation compounds
    Journal of Materials Chemistry, 2000
    Co-Authors: Teruyuki Nakato, Yoko Furumi, Naoshi Terao, Toshio Okuhara
    Abstract:

    Reactions of layered vanadium Phosphorus Oxides, VOPO4·2H2O and VOHPO4·0.5H2O, with aliphatic and aromatic amines were investigated with regard to the formation of intercalation compounds. VOPO4·2H2O was intercalated with 4-butylaniline, and the obtained intercalation compound was exfoliated by stirring in THF. The layered structure of the intercalation compound was reconstructed by removal of the solvent from the suspension of exfoliated solid, while ordering of the restacked layers was sensitive to the experimental conditions. The reactions with 4-butylaniline for prolonged periods caused partial collapse of the layered structure, indicating metastability of the intercalated structure. VOPO4·2H2O formed intercalation compounds with aniline and 4-anilinoaniline as well as 4-butylaniline. On the other hand, reactions with n-alkylamines, which are more basic than aromatic amines, brought about collapse of the layered structure of VOPO4·2H2O. In addition, VOHPO4·0.5H2O did not react with aromatic amines such as aniline and pyridine, while reactions with n-alkylamines did not give intercalation compounds but led to the formation of salts, where the structure of the host lattice was not retained.

Jeanclaude Volta - One of the best experts on this subject based on the ideXlab platform.

  • vanadium Phosphorus Oxides a reference catalyst for mild oxidation of light alkanes a review
    Comptes Rendus De L Academie Des Sciences Serie Ii Fascicule C-chimie, 2000
    Co-Authors: Jeanclaude Volta
    Abstract:

    Abstract Vanadium Phosphorus Oxides (VPO) are very promising materials for the mild oxidation of light alkanes. This is obvious from the considerable knowledge of the physicochemistry of the VPO catalytic system for which many complementary techniques have been used. The present state of the art and the possibilities for the development, in the future, of such a family of catalysts are discussed. It is highly possible that the discovery of new industrial processes for the oxidation of alkanes will stem from the improvement of vanadium Phosphorus oxide catalysts.

  • modification of vanadium Phosphorus Oxides used for n butane oxidation to maleic anhydride by interaction with niobium phosphate
    Catalysis Today, 2000
    Co-Authors: P Pries G De Oliveira, M Chavant, A S Riche, V Martin, Stefano Caldarelli, Jeanclaude Volta
    Abstract:

    Abstract A new family of vanadium Phosphorus Oxides (VPO) catalysts has been identified. It consists in a mixture of VPO with niobium phosphate (NbPO). The amorphous NbPO material is introduced during the preparation of the VOHPO4·0.5H2O precursor. It is observed that the VPO–NbPO catalyst is more rapidly activated and gives better performances (n-butane conversion and maleic anhydride selectivity) for mild oxidation of n-butane to maleic anhydride. VPO phases and the NbPO material have been identified in the VPO–NbPO precursor and in the VPO–NbPO catalyst. Nb in VPO crystals and V in NbPO particles have been respectively observed by EDX-STEM. No other VPO crystals than the VOHPO4, 0.5H2O precursor, and (VO)2P2O7 for the catalyst, have been identified by XRD and 31P NMR. 31P NMR by spin echo mapping and 31P MAS NMR have confirmed an interaction of the VPO precursor with Nb and of the NbPO amorphous material with V, as evidenced by EDX-STEM. This should be the reason for the observed improvement of the catalytic results by a redox effect of niobium on the VPO catalyst modifying the V5+/V4+ balance in a favourable way.

  • modifications of vanadium Phosphorus Oxides by aluminium phosphate for n butane oxidation to maleic anhydride
    Studies in Surface Science and Catalysis, 2000
    Co-Authors: Steve Holmes, V Martin, Andy Burrows, C. J. Kiely, Louisa Sartoni, Graham J Hutchings, Jeanclaude Volta
    Abstract:

    Aluminium phosphate associated with vanadium Phosphorus oxide is demonstrated in improving both the catalytic performance for the production of maleic anhydride from n-butane and the time of activation of the catalyst as compared to conventional vanadium Phosphorus oxide catalysts. Aluminium phosphate is prepared at a fixed pH and then added during the preparation of the VOHPO 4 , 0.5 H 2 O precursor. The morphology of the VPO precursor is influenced by the nature of the A1PO material. The VPO-A1PO catalyst is then activated in situ under an-butane/air atmosphere. During the activation, (VO) 2 P 2 O 7 is formed and the original amorphous A1PO material crystallizes. No new ternary VA1PO phase is observed. The improvement in the catalytic properties of the mixed VPO-A1PO oxide system cannot solely be explained in terms of a doped V(Al)P0 catalyst (Al/V= 1%) prepared independently, for which the catalytic performances are lower.

  • vanadium Phosphorus Oxides for n butane oxidation to maleic anhydride
    Applied Catalysis A-general, 1997
    Co-Authors: M Abon, Jeanclaude Volta
    Abstract:

    Abstract This publication presents recent developments of the knowledge of the vanadium Phosphorus Oxides used as catalysts for n -butane oxidation to maleic anhydride. We emphasize particularly the nature of the active phase, the active centres and the role of the redox and acido-basic properties contrasting informations between catalysts presenting different degree of disorder. The nature of the active oxygen species and the mechanistic aspects of the reaction are discussed from studies conducted in our laboratory and by comparison with the present knowledge.

  • On the role of microstructure of vanadium Phosphorus Oxides for propane oxidation to acrylic acid
    Studies in Surface Science and Catalysis, 1996
    Co-Authors: Nathalie Gribot-perrin, Jeanclaude Volta, Andy Burrows, C. J. Kiely, Michel Gubelmann-bonneau
    Abstract:

    Publisher Summary Up to now, most of the monomers used for the production of chemicals (plastics, paints, resins, and synthetic fibers) have been produced by the catalytic oxidation of olefins and aromatics. For economic reasons, in the future, technologies will use less expensive feedstocks. In this respect, the use of alkanes instead of olefins is particularly interesting. However, the direct oxidation of an alkane is a difficult challenge because the alkane is less reactive than the corresponding olefin, as are the final targeted oxygenate and corresponding intermediates. An example of this type of oxidation has been industrially developed with the oxidation of n-butane to maleic anhydride on Vanadium Phosphorus Oxide catalysts (VPO). The discovery of catalytic systems that are suitable for the oxidation of other alkanes to valuable monomers and the conditions for obtaining them now has to be considered. Few studies have been devoted to the synthesis of acrylic acid from propane by direct oxidation. Such a process should become industrially competitive, even at low conversion, with the condition that the selectivity of the transformation is preserved. Vanadium Phosphorus Oxides (VPO) still appear to be the most interesting catalytic system for this reaction. While VPO catalysts have been well studied and characterized for the oxidation of n-butane to maleic anhydride, there are no reported studies on the physicochemistry of this system in the case of the oxidation of propane. Moreover the experimental conditions that give the best yields to acrylic acid have to be identified, and the role of water vapor added in the feed has to be clarified. In this chapter, catalytic results for acrylic acid production are discussed with the physicochemical characteristics of the corresponding VPO materials to identify the conditions that give the best yield to acrylic acid.

Vadim V Guliants - One of the best experts on this subject based on the ideXlab platform.

  • phase transformations in mesostructured vanadium Phosphorus Oxides
    Catalysis Today, 2003
    Co-Authors: Moises A Carreon, Vadim V Guliants
    Abstract:

    Abstract Mesostructured lamellar, hexagonal and cubic vanadium–Phosphorus-oxide (VPO) phases were prepared employing cationic, anionic and alkylamine surfactants under mild conditions and low pH. The obtained mesophases displayed desirable vanadium oxidation states (+3.8 to +4.3) and P/V molar ratios ∼1.0 for the partial oxidation of n-butane to maleic anhydride. As-synthesized mesostructured VPO underwent phase transformations to various mesostructured and dense VPO phases depending on the post-synthesis treatment. The phase transformations of mesostructured VPO during Soxhlet extraction and thermal treatment in N2 have been observed for the first time. These transformations were explained by the changes in the surfactant packing parameter, g. Calcination in air produced more disordered mesostructures and dense VPO phases such as γ-VOPO4 and (VO)2P2O7.

  • Phase transformations in mesostructured vanadium–Phosphorus-Oxides
    Catalysis Today, 2003
    Co-Authors: Moises A Carreon, Vadim V Guliants
    Abstract:

    Abstract Mesostructured lamellar, hexagonal and cubic vanadium–Phosphorus-oxide (VPO) phases were prepared employing cationic, anionic and alkylamine surfactants under mild conditions and low pH. The obtained mesophases displayed desirable vanadium oxidation states (+3.8 to +4.3) and P/V molar ratios ∼1.0 for the partial oxidation of n-butane to maleic anhydride. As-synthesized mesostructured VPO underwent phase transformations to various mesostructured and dense VPO phases depending on the post-synthesis treatment. The phase transformations of mesostructured VPO during Soxhlet extraction and thermal treatment in N2 have been observed for the first time. These transformations were explained by the changes in the surfactant packing parameter, g. Calcination in air produced more disordered mesostructures and dense VPO phases such as γ-VOPO4 and (VO)2P2O7.

L M Cornaglia - One of the best experts on this subject based on the ideXlab platform.

  • the effect of preparation methods and activation strategies upon the catalytic behavior of the vanadium Phosphorus Oxides
    Catalysis Today, 1992
    Co-Authors: E A Lombardo, C A Sanchez, L M Cornaglia
    Abstract:

    Abstract The Catalyst precursors for the oxidation of n-butane to maleic anhydride were prepared using vanadium pentoxide and orthophosphoric acid. The former was reduced using different agents (HC1 and benzyl alcohol) and solvents (water, isobutyl and Isopropyl alcohols). The precursors were activated applying different strategies which were selected and adapted from the literature. The changes occurring in the solid were followed using XRD, XPS and 31P MAS NMR techniques. The Catalytic performance was evaluated using a flow reactor system. The equilibrated Catalysts obtained after 100–400 hours on stream contained vanadyl pyrophosphate as the only crystalline phase (XRD). The XPS data showed significant Phosphorus surface enrichment and the existence of only V(iv) on the surface. The solvent used and the activation strategy strongly influenced the Catalytic performance which could be traced through 31P NMR to the presence of small amounts of V(v) containing phases. The results are discussed in terms of the current literature.

Adrian O. Taylor - One of the best experts on this subject based on the ideXlab platform.

  • Preparation and characterisation of titania-supported vanadium–Phosphorus oxide catalysts
    Topics in Catalysis, 1999
    Co-Authors: Geoffrey C. Bond, Hamdy M. Ismail, Adrian O. Taylor
    Abstract:

    A series of vanadium–Phosphorus Oxides (mainly with V $$:$$ P $$ = 1:1 $$ ) supported on pigmentary anatase (10 m^2 g^-1) has been prepared using aqueous NH_4VO_3 and (NH_4)H_2PO_4 solutions, with loadings up to 11.3 wt%, equivalent to about 12.7 monolayers. Characterisation by X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction suggests that the main phase present at loadings below about 10 wt% is an amorphous V–P oxide which exists chiefly as blocks of disordered material. The presence of small amounts of crystalline $$\beta $$ -VOPO_4 and of V_2O_5 is indicated at the highest loadings, especially when $$1:3$$ and $$3:1$$ V $$:$$ P ratios are used. The two materials having the lowest loadings are active for methanol oxidation at 473–533 K, and show high selectivity to formaldehyde.