Vanadyl Hydrogen Phosphate Research Articles

Crystallisation of VOHPO 4·0.5H 2O in the presence of a surfactant

The formation of vanadyl hydrogen phosphate hemihydrate (VOHPO 4·0.5H 2O) by progressive attachment of phosphorous to a vanadium oxide lamellar phase in the presence of cetyltrimethylammonium bromide (CTAB) is described. Evidence from nuclear magnetic resonance (NMR), XPS, X-ray diffraction (XRD) and scanning electron microscopy (SEM) is presented for the initial formation of a vanadium oxide lamellar structure with no long-range order to which phosphate is then progressively attached. Phosphate attachment leads to lamellar collapse with the resultant formation of the hemihydrate phase, VOHPO 4·0.5H 2O.

Novel platinum incorporated vanadium phosphates and their catalytic activity

Abstract Platinum has been incorporated into the layered vanadyl hydrogen phosphate VOHPO 4 ·0.5H 2 O in different ways depending upon the medium of its preparation. The phase obtained by the introduction of platinum during the synthesis of VOHPO 4 ·0.5H 2 O in aqueous medium is a new crystalline phase with mixed-valent vanadium containing Pt 2+ species. This phase forms a novel hydrogen insertion compound involving hydrogen spillover from the incorporated platinum onto the VPO matrix. On the other hand, the incorporation of platinum during the synthesis of the hemihydrate in organic medium gives rise to a phase containing both metallic platinum and an amorphous Pt 2+ containing VPO phase. Both these platinum incorporated phases have been found to be active catalysts for reduction and oxidation reactions such as the hydrogenation of nitrobenzene and the oxidation of tetrahydrofuran with the activity varying quite markedly with the mode of incorporation.

Vanadyl (IV) Hydrogen Phosphate Hemihydrate (VOHPO4⋅0.5H2O) by XPS

The XPS spectra of vanadyl hydrogen phosphate were collected with a VSW HA150 using monochromatic Al Kα x-radiation. The valence band region is determined by the features of the HPO42− ion which shows subtle but significant differences from the valence band region of the orthophosphate ion (PO43−). The valence band, survey, V 2p, V 3p, O 1s, P 2p, P 2s, and C 1s are reported.

Flux growth of vanadyl pyrophosphate, (VO)(2)P(2)O(7), and spin dimer analysis of the spin exchange interactions of (VO)(2)P(2)O(7) and vanadyl hydrogen phosphate, VO(HPO(4)).0.5H(2)O.

Large transparent blue crystals of vanadyl pyrophosphate, (VO)(2)P(2)O(7), were grown from a phosphorus pentoxide flux, and the single-crystal X-ray structure of (VO)(2)P(2)O(7) was determined with high precision. On the basis of spin dimer analysis, we examined the spin exchange interactions of (VO)(2)P(2)O(7) and its precursor VO(HPO(4)).0.5H(2)O. Our analysis of (VO)(2)P(2)O(7) using two high-precision crystal structures shows unambiguously that the V3-V4 chain has a larger spin gap than does the V1-V2 chain and that the super-superexchange (V-O...O-V) interaction is stronger than the superexchange (V-O-V) interaction in the V3-V4 chain while the opposite is true in the V1-V2 chain. Our analysis of VO(HPO(4)).0.5H(2)O reveals that the superexchange interaction must dominate over the super-superexchange interaction, in disagreement with the conclusion from a powder neutron scattering study of VO(DPO(4)).0.5D(2)O.

Novel vanadium phosphate phases as catalysts for selective oxidation

In our effort to induce novel modifications in the structure of some important vanadium phosphate phases used as selective oxidation catalysts, it has been observed that metal ions such as Zn2+, Ni2+, Pd2+can be incorporated into the vanadyl hydrogen phosphate VOHPO40.5H2O phase in very different ways depending upon the medium of preparation. It has been found that the metal ions are either substituted into the lattice with retention of structure of the parent compound or intercalated between the layers of a new mixed-valent phase. These new metal-incorporated phases are catalytically active and the palladium incorporated compound in particular displays shape selective catalysis for different oxidation and reduction reactions. In another approach, the preparation of VOHPO40.5H2O) has been modified to give a novel crystalline phase containing mixed-valentvanadium and having NH3 species bound to the lattice. This phase could be a potential catalyst for ammoxidation reactions. In addition, novel mesostructured vanadium phosphate phases have been prepared using a long-chain amine as the templating agent involving a ligand templating mechanism of formation.

Characterization and catalytic activity of novel palladium-incorporated vanadium phosphates

Palladium has been introduced into the layered vanadyl hydrogen phosphate hemihydrate VOHPO 4·0.5H 2O in different ways depending upon the medium of preparation. In aqueous medium, the introduction of palladium leads to the formation of a new phase containing mixed valent vanadium whereas in the preparation in organic medium, the palladium appears to substitute into the lattice of the parent compound. The palladium-incorporated compounds have been found to be catalytically active, both for oxidative coupling as well as for hydrogenation reactions, with the activity and selectivity varying quite markedly with the mode of incorporation.

Hybrid Open Frameworks. Hydrothermal Synthesis, Structure Determinations, and Magnetic Behavior of (VIVO)2(H2O){O3P–(CH2)3–PO3}·2H2O: A New Vanado-alkyldiphosphonate Closely Related to VO(HPO4)·0.5H2O

(VIVO)2(H2O) {O3P–(CH2)3–PO3}·2H2O was hydrothermally synthesized from a mixture of VOSO4·5H2O:H2PO3– (CH2)3–PO3H2:H2O in a molar ratio 1:0.5:250 and heated for 72 hours to 170°C. Its structure was determined from powder X-ray diffraction data. It crystallizes in the orthorhombic space group Immm (No. 71) with a=16.8210(5) Å, b=9.3790(3) Å, c=7.4568(2) Å, V=1176.4(1) Å3, Z=4. The pillared framework is built up from inorganic layers covalently linked via P–C–C–C–P bonds. The inorganic layers are similar to those encountered in a VO(HPO4)·0.5H2O bidimensional compound described previously. The dimers of face-shared VO5(H2O) octahedra are linked by PO3C phosphonate groups instead of PO3(OH) groups in the vanadyl hydrogenphosphate. The terminal hydroxyl groups in the latter are substituted by the carbons of the organic chains which link two layers, giving the three-dimensional character of the structure. The magnetic behaviors of the two compounds are compared.

Vanadyl hydrogenphosphate sesquihydrate as a precursor for preparation of (VO) 2P 2O 7 and cobalt-incorporated catalysts

Vanadyl hydrogenphosphate sesquihydrate (VOHPO 4·1.5H 2O) was prepared by reduction of VOPO 4·2H 2O suspended in refluxed 1-butanol and activated at 480°C over 10 h on-stream to give (VO) 2P 2O 7, which revealed high specific activity per unit surface area in the vapor-phase oxidation of n-butane. Cobalt-modified (VO) 2P 2O 7 catalysts were prepared in the present work by intercalating sesquihydrate precursor with cobaltous acetate employing 1-butanol as solvent. The catalysts prepared from cobalt-intercalated precursor showed high specific activity, but both selectivities to maleic anhydride and surface area decreased with increasing cobalt-contents. Presumably, intercalated cobalt species retarded topotactic dehydration of layered precursor to afford crystalline active species (VO) 2P 2O 7, leading to an increase in unfavorable combustion activity due to pentavalent β-VOPO 4 species. The activity of catalysts prepared for reference by kneading vanadyl hydrogenphosphate hydrates with an additive Co 2P 2O 7 was interpreted as the variation in surface area, and cobalt has none of positive effects in these catalysts.

Tribomechanical pretreatment of vanadium phosphates: structural and catalytic effects

The influence of the tribomechanical pretreatment of the precursor vanadyl hydrogenphosphate hemihydrate, VOHPO4·0.5H2O, prepared in aqueous medium and of the catalyst vanadyl pyrophosphate, (VO)2P2O7, on the structural and catalytic properties of (VO)2P2O7 in the oxidation of n-butane to maleic anhydride was investigated. Due to the pretreatment the activity and selectivity of the catalyst were markedly increased. The increase in catalytic performance is explained as an effect of the particle size in connection with lattice imperfections.

On the rehydration of vanadyl pyrophosphate to vanadyl hydrogenphosphate hemihydrate

Vanadyl pyrophosphate-based VPO catalysts for butane oxidation to maleic anhydride can be completely rehydrated in the solid phase into their vanadyl hydrogenphosphate hemihydrate precursors which again can be transformed into vanadyl pyrophosphate thus enabling a reuse of spent catalysts.

ChemInform Abstract: Novel Method for Synthesis of Well‐Crystallized Vanadyl(2+) Hydrogen Phosphate Hemihydrate: Crystallization in Organic Media Containing a Small Amount of Water.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Redetermination of Monoclinic VOHPO4.2H2O

Single crystals of monoclinic α-VOHPO4.2H2O, α-oxovanadium(IV) hydrogen phosphate dihydrate, were synthesized by hydrothermal reaction. The structure was refined with good accuracy (R = 0.018) and the results are compared with those of an earlier structure determination from X-ray powder data [Le Bail, Amoros & Beltran-Porter (1989). Eur. J. Solid State Inorg. Chem. 26, 419–426]. Significant differences in bond lengths were found. The structure consists of vanadyl hydrogenphosphate layers running along [100]. The layers are connected via hydrogen bonds.

New precursors to vanadium phosphorus oxide catalysts

New precursors to vanadium phosphorus oxide catalysts have been synthesized based on alteration of the layered structure found in the active VPO catalysts. n-Alkyl amine intercalation compounds of vanadyl hydrogen phosphate hemihydrate have been prepared that are transformed into active vanadyl pyrophosphate catalysts. Catalytic performance for selective oxidation of n-butane to maleic anhydride improves with length of alkyl chain. Vanadyl phosphonates and vanadyl phosphite have been prepared containing vanadyl dimer structures that are thermally transformed into vanadyl pyrophosphate below 650 K for the phosphonates and 550 K for the phosphite. The VPO catalyst from the vanadyl phosphite precursor had a high surface area of 35 m 2/g, and displayed better selectivity for maleic anhydride from n-butane oxidation than the conventional unpromoted catalyst. Mixed vanadyl phosphite-phosphate materials, which were found to be very reactive for intercalation of amines, were intercalated with 3-aminopropyltriethoxysilane and calcined to produce the first thermally stable pillared VPO catalyst.

Evidence for a hydrogen insertion compound of novel palladium incorporated vanadyl hydrogen phosphates

Palladium is shown to be incorporated into the vanadyl hydrogen phosphate phase VOHPO4·0.5H2O in different ways depending on the medium used for preparation; temperature programmed reduction (TPR) studies provide evidence for the formation of a hydrogen insertion compound of one of these palladium incorporated vanadyl phosphates.

Transformation of VOHPO 4 · 1/2H 2O to (VO) 2P 2O 7: crystallographic, microstructural, and mechanistic aspects

A detailed study of the transformation of the butane oxidation catalyst precursor VOHPO 4 · 1/2H 2O to γ-(VO) 2P 2O 7 is reported. The vanadyl hydrogen phosphate precursors used in this study were in the form of single crystals and powders, each prepared from aqueous media. Electron microscopy and X-ray diffraction clearly show the transformation to be topotactic: single crystals are converted to pseudomorphs which are unchanged in size or shape with respect to the starting crystals. The pseudomorphs are made up of highly-oriented vanadyl pyrophosphate microcrystals. A large contraction of the atomic structure in the direction perpendicular to the basal plane induces cracks and voids within the crystal. A transformation mechanism involving phosphorus-atom inversion, along with supporting MNDO SCF-MO calculations, is presented. This mechanism accounts for at least some of the interlayer, crystallographic disorder that is often attributed to the sterically hindering effects of residual organics. The generation of cracks to accommodate unit cell shrinkage along the thin dimension of the crystal plates creates additional basal plane surface area that may be beneficial in terms of catalytic performance.

Preparation and Characterization of Vanadyl Hydrogen Phosphate Hydrates; VO(HPO4)·1.5H2O and VO(HPO4)·0.5H2O

Abstract A new phase of vanadyl(IV) hydrogen phosphate sesquihydrate, VO(HPO4)·1.5H2O, has been obtained by the reduction of VOPO4·2H2O with 1-butanol. The unit cell is the orthorhombic system with lattice constants a = 7.43 Å, b = 9.62 Å, and c = 7.97 Å. in space group Pmmn.

TEM phase transformation study of (VO)2P2O7 catalyst

(VO)2P2O7 (VPO) is known to act as a heterogeneous catalyst in the oxidation of n-butane to maleic anhydride. DuPont has developed a new circulating fluid bed process for this reaction, and first commercial plant using this technology is scheduled to start up in early 1996. VPO catalyst is typically formed by transforming the vanadyl hydrogen phosphate precursor (VOHPO4. 1/2H2O) to the vanadyl pyrophosphate active phase. It was the object of the current study to develop a more fundamental understanding of this phase transformation.Transformation conditions were 500° - 700° C in nitrogen. The hydrated precursors used in this study were in the form of plate-shaped single crystals. The crystallographic convention is given in Table 1. Microstructural and morphological changes associated with the phase transformation were studied at scales ranging from the mm to the nm range using scanning electron microscopy (Hitachi S-4000) and transmission electron microscopy (JEM 2000FX). Figure la is an SEM showing the corner of a precursor crystal plate with the c axis indicated.

Synthesis and Characterization of Vanadyl Phosphite, VIVOHPIIIO3.cntdot.1.5H2O

Vanadyl(1V) phosphite, VOHP03.1.5H20, was synthesized by reduction of V205 in refluxing alcohol solutions (ethyl, isopropyl, and isobutyl alcohols) with subsequent addition of H3P03. X-ray diffraction suggests an orthorhombic space group. Magnetic susceptibility data indicate the presence of exchange coupled vanadyl dimers associated with face-shared vanadyl octahedra similar to vanadyl hydrogen phosphate hemihydrate, VOHP04.0.5HzO. Vanadyl(IV) phosphite is a layered solid with an interlayer spacing of 7.27 A. n-Alkylamines intercalated into the layered structure as siqgle or double layers depending on the amineto-host ratio, and the interlayer spacings, d (A), increased linearly with the carbon number, n,, as d = 7.72 + 0.85nC (monolayers), and d = 6.49 + 1.82~~~ (bilayers).

Characterization and catalytic activity of novel compounds containing metal ions incorporated into a layered vanadyl phosphate

The addition of metal ions such as Zn2+, Ni2+ and Pd2+ during the preparation of the layered vanadyl hydrogen phosphate VOHPO4·0.5H2O in aqueous medium, leads to the formation of a new phase containing mixed-valent vanadium. In contrast, when the same metal ions are added during the preparation of the vanadyl hydrogen phosphate in organic medium, the structure of the parent compound is retained and the metal ions appear to be present in the lattice. The metal ions incorporated into the vanadyl hydrogen phosphate prepared in different media have been found to be catalytically active, with the activity depending upon the mode of incorporation of the metal ion.

Intercalation of Aliphatic Amines into the Layered Structure of Vanadyl(IV) Hydrogen Phosphate Hemihydrate (VOHPO4.cntdot.0.5H2O)

The vanadyl(IV) hydrogen phosphate hemihydrate, VOHPO[sub 4][center dot]0.5H[sub 2]O, is a pyrolytic precursor of the vanadyl(IV) pyrophosphate phase, (VO)[sub 2]P[sub 2]O[sub 7], generally believed to be the active phase in the selective oxidation of n-butane into maleic anhydride. Pyrolytic transformation into the pyrophosphate phase occurs with conservation of a morphology of the material. VOHPO[sub 4][center dot]0.5H[sub 2]O is a layered hydrogen phosphate, where -POH groups form interlayer hydrogen bonds with the water molecules shared by two face-linked vanadyl octahedra. The structure of the hemihydrate is similar to that of [alpha]-zirconium hydrogen phosphate ([alpha]-ZrP), where hydrogen bonds are within the same layer and -POH groups are also pointed into the interlayer space. In contrast to [alpha]-ZrP, where extensive data exist, intercalation chemistry of the layered vanadyl(IV) hydrogen phosphate hemihydrate at present is a terra incognita. This paper reports the results of the first systematic study of VOHPO[sub 4][center dot]0.5H[sub 2]O intercalation with aliphatic amines as a new route to novel vanadyl(IV) phosphate phases. N-Alkylamines have been commonly known as excellent intercalation agents for testing the intracrystalline reactivity of layered oxides. Intercalated alkylamines may also facilitate introduction of thermostable guest molecules, or [open quotes]pillars[close quotes], by ion exchange producing microporous materials whichmore » can modify catalytic and sorptive properties. 9 refs., 6 figs., 2 tabs.« less