n-Butane Oxidation over γ-Al2O3 Supported Vanadium Phosphate Catalysts

Four vanadium phosphate catalysts supported onγ-Al_2O_3(20 wt%)were synthesized via wetness impregnation of VOHPO_4·0.5H_2O precursor and calcined for different durations(6,10,30 and 75 h)at 673 K in a reaction flow of n-butane/air mixture.The samples calcined for 6 and 10 h produced only a single phase of(VO)_2P_2O_7.However,the VOPO_4 phase(β-VOPO_4)was detected and became more prominent with only a minor pyrophosphate peaks were found after 30 h of calcination.All these pyrophosphate peaks disappeared after 75 h of calcination.The formation of V~(5 )phase was also observed in the SEM micrographs.The redox properties and the nature of oxidants of the catalysts employed in this study were investigated by H_2-TPR analysis.Selective oxidation of n-butane to maleic anhydride(MA) over these catalysts shows that the percentage of n-butane conversion decreases with the transformation of the catalysts from V~(4 )to V~(5 )phases.An appropriate ratio of V~(5 )/V~(4 )can enhance the performance of the VPO catalyst.However,a higher amount of V~(5 )and its associated oxygen species are responsible to promote the MA selectivity.     

Effect of tellurium promoter on vanadium phosphate catalyst for partial oxidation of n-butane

Te-promoted (1%) vanadium phosphate catalyst (VPDTe) was prepared via VOPO4·2H2O by calcining its precursor VOHPO4·0.5H2O in a flow of n-butane/air.VPDTe catalyst has resulted a higher existence of V5+ phase with V5+/V4+ ratio of 0.23.SEM micrographs show that Te addition altered the arrangement of the platelets from "rose-like" clusters to layer with irregular shape.Te addition has also markedly lowered the reduction activation energies of the vanadium phosphate catalyst as revealed by TPR profile.The amount of active oxygen species associated with V4+ phase of the Te promoted catalyst was significantly higher than those of the unpromoted catalyst.These observations suggest that high mobility and availability of reactive oxygen species contributed to the enhancement of n-butane conversion up to 80% at 673 K,while only 47% over unpromoted catalyst (2400 h-1,1.7% n-butane in air).     

Synthesis and characterization of Cr-MSU-1 and its catalytic application for oxidation of styrene

Chromium-containing mesoporous silica material Cr-MSU-1 was synthesized using lauryl alcohol-polyoxyethylene (23) ether as templating agent under the neutral pH condition by two-step method. The sample was characterized by XRD, TEM, FT-IR, UV-Vis, ESR, ICP-AES and N₂ adsorption. Its catalytic performance for oxidation of styrene was studied. Effects of the solvent used, the styrene/H₂O₂ mole ratio and the reaction temperature and time on the oxidation of styrene over the Cr-MSU-1 catalyst were examined. The results indicate that Cr ions have been successfully incorporated into the framework of MSU-1 and the Cr-MSU-1 material has a uniform worm-like holes mesoporous structure. After Cr-MSU-1 is calcined, most of Cr³⁺ is oxidized to Cr⁵⁺ and Cr⁶⁺ in tetrahedral coordination and no extra-framework Cr₂O₃ is formed. The Cr-MSU-1 catalyst is highly active for the selective oxidation of styrene and the main reaction products over Cr-MSU-1 are benzaldehyde and phenylacetaldehyde. Its catalytic performance remains stable within five repeated runs and no leaching is noticed for this chromium-based catalyst.     

Characterisation and thermal analysis of vanadium(II) oxalate

The synthesis, compositional formula and mode of thermal decomposition of a compound for which there existed only a single literature reference [1] have been investigated in this work.The product of the aqueous phase reaction between vanadium(II) ions and oxalate ions at lowpH has been identified: vanadium(II) oxalate dihydrate, VC₂O₄·2H₂O, has been characterised by thermal methods of analysis supported by a range of complementary analytical techniques.The findings of a previous author [1] have been confirmed and extended in this work. In addition, a synthetic procedure for the preparation of gram quantities of vanadium(II) oxalate dihydrate, VC₂O₄·2H₂O, is reported here for the first time.The oxalate compound prepared was found to be remarkably stable in relation to aerial oxidation, unlike other representative solid state compounds of the vanadium(II) oxidation state. Vanadium(II) oxalate dihydrate may, therefore, serve as an important intermediate in the future synthesis of other vanadium(II) compounds.We would wish to thank Mr. S. Sutcliffe, University College Salford, for providing the Thermal Analysis data and also Mr. S. Unsworth, Magnesium Electron, Clifton, Manchester, for providing the XRD data.     

掺Ni钒磷氧化物催化剂的合成和表征

以VOPO4.2H2O为原料制备了钒磷氧化物催化剂,考察了镍掺杂(1%,2%和5%)对该催化剂的影响.低掺杂量的Ni明显提高了活性晶格氧物种O-的数量,降低了V5 和V4 相的还原峰温.粉末X射线衍射、程序升温还原和化学分析结果表明,高掺杂量的Ni促使V5 物相生成并抑制V4 物相出现.高含量与V5 相关的氧物种会降低正丁烷的转化率,但会提高马来酸酐的选择性.     

Synthesis and ion-exchange properties of crystalline titanium and zirconium phosphates

The preparation of novel types of inorganic ion-exchangers, titanium and zirconium phosphates and their ion-exchange properties towards strontium ions, are reported and discussed. Ti(HPO₄)₂·2H₂O is shown to be very stable to hydrolysis and to have high exchange capacity in strongly acid medium. In the case of zirconium phosphate, the titration curves with alkaline earth metal hydroxides are strongly affected by hydrolysis of the exchanger and precipitation of insoluble phosphate. The degree of conversion of the exchanger at which phosphate precipitation begins was found to be 80% for Sr²⁺. The comparison of Ti(HPO₄)₂·2H₂O with the corresponding zirconium phosphate dihydrated phase suggests that the former possesses a lattice structure different from that reported for the monohydrated exchanger.This revised version was published online in November 2005 with corrections to the Cover Date.     

Effect of direct ultrasound synthesis via a sesquihydrate route on bismuth-promoted vanadyl pyrophosphate catalysts

A series of 1, 3, and 5% Bi-doped vanadium phosphate catalyst catalysts were prepared via sesquihydrate route using direct ultrasound method and were denoted as VPSB1, VPSB3, and VPSB5, respectively. These catalysts were synthesized solely using a direct ultrasound technique and calcined in a n-butane/air mixture. This study showed that catalyst synthesis time can be drastically reduced to only 2 hr compared to conventional 32–48 hr. All Bi-doped catalysts exhibited a well-crystallized (VO)₂P₂O₇ phase. In addition, two V⁵⁺ phases, that is, β-VOPO₄ and α_II-VOPO₄, were observed leading to an increase in the average oxidation state of vanadium. All catalysts showed V2p_3/2 at approx. 517 eV, giving the vanadium oxidation state at approx. 4.3–4.6. Field-emission scanning electron microscopy micrographs showed the secondary structure consisting of thin and small plate-like crystal clusters due to the cavitation effect of ultrasound waves. VPSB5 showed the highest amount of oxygen species removed associated with the V⁵⁺ and V⁴⁺ species in temperature-programmed reduction in H₂ analyses. TheX-ray absorption near edge structure (XANES) measurement showed the occurrence of vanadium oxide reductions in hydrogen gas flow, indicating the presence of V⁴⁺ and V⁵⁺ species. Higher average valence states of V⁵⁺, indicating more V⁵⁺ phases, were present. The addition of bismuth has increased the activity and selectivity to maleic anhydride.     

Physico-chemicals and catalytic properties of manganese-promoted vanadium phosphate (VPO) catalyst

The addition of 1% Mn promoter to vanadium phosphate catalyst led to doubling of the specific surface area from 20.3 (unpromoted) to 39.4 m² g⁻¹. The XRD pattern of the Mn-promoted catalyst gave only the characteristics of the (VO)₂P₂O₇ phase, indicating that the Mn was incorporated into the crystal lattice of the catalyst. The Mn-promoted catalyst was also twice as active in removing the total amount of oxygen. However, since the only oxygen species related to V⁴⁺ being removed and no oxygen species associated with V⁵⁺ was observed, the n-butane conversion was not much improved as compared to the unpromoted counterpart. A necessary amount and distribution of the V⁵⁺ phase in a well crystalline V⁴⁺ phase is essential in order to enhance the catalytic performance in the mild oxidation of n-butane to maleic anhydride.     

Synthesis of vanadium-phosphorus oxide catalysts supported on pyrogenic silica and titanium dioxide

Various methods for the preparation of vanadium-phosphorus oxide (VPO) catalysts supported on aerosils A-300 and A-50 and TiO₂ were studied: a traditional method (in an organic solvent under varying the support addition time, the nature of the reducing agent, and the degree of reduction of vanadium oxide) and barothermal and mechanochemical syntheses. With the use of XRD analysis, it was found that the composition of the resulting VPO phase depends on the time of support addition to the synthesis and the temperature of thermal treatment. Conditions for the formation of a supported phase of VOHPO₄·0.5H₂O, the precursor of the active component (VO)₂P₂O₇, were determined. The presence of vanadium in an oxidation state of +4 was demonstrated using EPR and UV-VIS spectroscopy. The specific surface areas and pore structures of the synthesized catalysts were determined. The catalytic properties of samples in the reactions of n-butane oxidation in an excess of the hydrocarbon and oxidative ethane dehydrogenation were studied. It was found that, as compared with traditional bulk VPO catalysts, the use of the synthesized supported VPO catalysts made it possible to improve the process characteristics of n-butane oxidation and did not change these characteristics in the reaction of oxidative ethane dehydrogenation.     

On the topotactic dehydration of VOHPO4 · 0.5 H2O into vanadyl pyrophosphate

The thermal analysis (DTA, TGA) of the dehydration under inert atmosphere of the vanadyl hydrogen phosphate hydrate VOHPO₄ · 0.5 H₂O recently studied, together with the characterization of both starting and final compounds (XRD, ir, and uv-visible spectroscopies) show that pseudomorphic vanadyl pyrophosphate is obtained in these conditions. This form γ-(VO)₂P₂O₇ is the active and selective catalyst in butane oxidation to maleic anhydride whereas β-(VO)₂P₂O₇ is selective in butene oxidation only. Pseudomorphic relations between VOHPO₄ · 0.5 H₂O and γ-(VO)₂P₂O₇ are evidenced by the comparison of XRD patterns, SEM and TEM experiments, and justified with the help of both structures. The low values of the activation energies calculated from kinetic data, E₁ = 21.4 and E₂ = 24.7 kcal · mole^?1 show that the dehydration of the hydrate and the formation of γ are topotactic, this hypothesis is confirmed and the mechanism stated precisely in view of the preceding results.     

Synthesis and properties of (VO)<Subscript>0.09</Subscript>V<Subscript>0.18</Subscript>Mo<Subscript>0.82</Subscript>O<Subscript>3</Subscript> · 0.54H<Subscript>2</Subscript>O microrods

The (VO)_0.09V_0.18Mo_0.82O₃ · 0.54H₂O microrods of hexagonal symmetry system with the unit cell parameters a = 10.586 Å and c = 3.698 Å were obtained for the first time under hydrothermal conditions (T = 160°C, τ = 30?50 h). Particles were 1–2 μm in diameter and up to 45 μm in length. The compound is thermally stable up to 469°C. The core-electron Mo3d, V2p, and O1s and valence-band X-ray photoelectron spectra and IR spectra of the samples were studied. The molybdenum atoms in the complex oxide have the oxidation state Mo⁶⁺. The vanadium atoms introduced into the h-MoO₃ lattice in molybdenum positions have the oxidation state V⁵⁺. Approximately one-third of vanadium atoms as vanadyl ions (VO)²⁺ are located in the channels of h-MoO₃ lattice, thus stabilizing the latter.     

NH3 TPD study and thermal behaviour of vanadium-exchanged titanium phosphates as catalysts

The ion exchange technique was employed for the preparation of VO²⁺ modified titanium phosphates as catalysts for the selective reduction of NO with NH₃. The samples were prepared by contacting with a vanadyl sulphate solution different precursor materials, amorphous, crystalline or sodium half exchanged titanium phosphate. The vanadium contents of modified phosphates were in the range 0.08–2.3 wt%. XRD and thermal analysis TG/DTA showed that vanadium loading does not cause structural modification in hydrogen titanium phosphate. A vanadyl containing phase was obtained when half sodium titanium phosphate was employed. The NH₃ TPD measurements indicated the presence of a wide distribution of NH₃ adsorbing sites with medium-high strength. Catalytic activity measurements were performed under dilute conditions. It was found that the presence of vanadium even in low amounts strongly promote the catalytic activity.     

铋和镍对钒磷氧化物催化剂性能的影响YunHinTaufiq-Yap,ChoonSeonYuen,Nawi简

Vanadium phosphorus oxide (VPO) catalysts were synthesized by the dihydrate method which involved the two steps for the preparation of the dihydrate (VOPO₄×2H₂O) and the precursor hemihydrate (VOHPO₄×0.5H₂O). Bi and Ni salt were added into the mixture of VOPO₄×2H₂O and isobutanol, and the obtained precursors were calcined in a flow of a n-butane/air mixture to produce the promoted VPO catalysts. The catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption-desorption, inductively coupled plasma-atomic emission spectroscopy, scanning electron microscopy (SEM), and H₂ temperature-programmed reduction (H₂-TPR). Their catalytic properties were tested using a fixed-bed microreactor. All the catalysts gave main XRD peaks at 2θ = 22.9°, 28.5°, and 30.0°, attributing to the (020), (204), and (221) planes of the pyrophosphate phase (VO)₂P₂O₇, respectively. The promoted catalysts have smaller crystallite size and higher specific surface areas. SEM micrographs revealed the formation of more prominent plate-like crystallites that were arranged as rosette clusters. H₂-TPR results showed that the promoted catalysts had lower reduction peak temperatures and possessed higher amounts of V⁵⁺-O^2- and V⁴⁺-O^- pairs, which gave higher selectivity and activity in the selective oxidation of n-butane to maleic anhydride.     

XPS study of nanorods of doped vanadium oxide MxV2O5 · nH2O (M = Na, K, Rb, Cs)

Nanorods of vanadium oxide doped with alkali metal ions M _x V₂O₅ · nH₂O (M = Na, K, Rb, Cs, x = 0.31–0.44) have been obtained under hydrothermal conditions. The particles are 30–80 nm in diameter and a few micrometers in length. The chemical state of atoms and their concentration ratios have been studied by XPS. It has been shown that vanadium atoms are in two oxidation states V⁵⁺ and V⁴⁺ and the concentration of vanadium(IV) ions directly depends on the alkali metal. The X-ray photoelectron spectra of the valence bands of M _x V₂O₅ · nH₂O (M = Na, K, Rb, Cs) nanorods have been measured and interpreted.     

Synthesis, structure, and magnetic properties of two novel lanthanide-organic frameworks

Two novel metal-organic frameworks, {[Eu(phen)(NDA)1.5(H2O)]}n ((1); NDA = 2,6-naphthalenedicarboxylate ions, phen = 1,10-phenanthroline) and {[Gd(phen)(NDA)1.5]·0.5H2NDA}n (2), have been synthesized under hydrothermal conditions. The structure analyses of 1 and 2 reveal that the two compounds belong to the triclinic system with space group P-1. Compound 1 features a 2D lattice structure while compound 2 displays a novel 3D architecture. The two frameworks were further characterized by elemental analyses, l...     

Transport properties of vanadium ions in cation exchange membranes:: Determination of diffusion coefficients using a dialysis cell

Diffusion coefficients of vanadium ions in cation exchange membranes are of interest because they allow to calculate the ion exchange across the membrane in an all vanadium redox flow battery which leads to undesired cross contamination and energy losses in the battery system. Diffusion coefficients of V²⁺, V³⁺, VO²⁺ and VO⁺₂ ions in CMS, CMV and CMX cation exchange membranes have been determined by measuring the ion exchange fluxes of these ions with H₃O⁺ ions using a dialysis cell. The experimental data are evaluated on the basis of integrated flux equations which require also ion exchange sorption equilibria obtained already in previous work. The lowest diffusion coefficients are observed in the CMS membrane for all vanadium ions. This membrane turns out to be the most suitable one for being applied in a vanadium battery since it is expected to prevent most effectively cross contamination of vanadium ions.     

Brushite (Ca,M)HPO4, 2H2O doping with bioactive ions (M = Mg2+, Sr2+, Zn2+, Cu2+, and Ag+): a new path to functional biomaterials?

Dicalcium phosphate dihydrate, DCPD (CaHPO₄·2H₂O), brushite, is an important calcium phosphate compound encountered in mineralized tissues and used in medicine, especially in bone cement formulations. However, the use of DCPD as direct implantable biomaterial has not received dedicated attention. In addition, the possibility to dope DCPD with biologically active ions to modulate its performances was not systematically explored. We have investigated in depth the doping of DCPD with Mg²⁺, Sr²⁺, Zn²⁺, Cu²⁺, and Ag⁺ ions. Clear modifications in terms of chemical composition, particle size, pore distribution, crystal morphology, and affinity for water were pointed out. Then, the samples were cultured with human adipose-derived stem cells to explore cytotoxicity and proliferation. Various behaviors were noticed dependent on the incorporated metal ions. Such DCPD compounds associated with bioactive metal ions, and particularly Ag⁺ and Zn²⁺, appear promising as a new family of reactive materials for use, as such or in combination, in bone-related applications.     

Oxidation/reduction studies on ZryU1−yO2+x and delineation of a new orthorhombic phase in U-Zr-O system

In this communication, we report the oxidation and reduction behavior of fluorite type solid solutions in U-Zr-O. The maximum solubility of ZrO₂ in UO₂ lattice could be achieved with a mild oxidizing followed by reducing conditions. The role of valency state of U is more dominating in controlling the unit cell parameters than the incorporated interstitial oxygen in the fluorite lattice. The controlled oxidation studies on U-Zr-O solid solutions led to the delineation of a new distorted fluorite lattice at the U:Zr=2:1 composition. The detailed crystal structure analysis of this ordered composition Zr_0.33U_0.67O_2.33 (ZrU₂O₇) has been carried from the powder XRD data. This phase crystallizes in an orthorhombically distorted fluorite type lattice with unit cell parameters: a=5.1678(2), b=5.4848(2), c=5.5557(2) Å and V=157.47(1) Å³ (Space group: Cmcm, No. 63). The metal ions have distorted cubical polyhedra with anion similar to the fluorite structure. The excess anions are occupied in the interstitial (empty cubes) of the fluorite unit cell. The crystal structure and chemical analyses suggest approximately equal fractions of U⁴⁺ and U⁶⁺ in this compound. The details of the thermal stability as well as kinetics of formation and oxidation of ZrU₂O₇ are also studied using thermogravimetry.     

Systematic Study of the Interaction Between VIV Centres and LnIII Ions in Well Defined {V 2 IV LnIII}{AsIIIW9O33}2 Sandwich-Type Clusters: Part 2

The gadolinium (Gd) member of a new type of heteropolytungstates that contain one lanthanide and two transition metal ions in a triangular arrangement is reported. The compound NaK₆Gd_0.33 [((VO)₂Gd(H₂O)₄K₂(H₂O)₂(Na)(H₂O)₂)(α-B-AsW₉O₃₃)₂]·24H₂O (1) was prepared from acidified aqueous solutions of Na₂WO₄·2H₂O, As₂O₃ and VOSO₄·5H₂O to which Gd³⁺ ions were added. The single crystal X-ray structure analysis (monoclinic, space group P2₁/m) shows that the anion consists of two [α-B-As^IIIW₉O₃₃]^9? trilacunary Keggin-type units linked by two VO²⁺, one Gd³⁺ as well as weakly by two K⁺ and one Na⁺ ions, resulting in a sandwich-type structure with idealized C _2v symmetry. The problem of positioning crystal lattice and special polyoxometalate sites with different cations is discussed also in connection with supramolecular chemistry aspects and as an option for further research. A fit of the magnetic susceptibility yielded exchange coupling constants of J _VV = ?2.55 cm^?1 (anti-ferromagnetic) between the vanadium ions and J _GdV = 0.6 cm^?1 (ferromagnetic) between the Gd and each of the two vanadium ions. The complete magnetochemical analysis also revealed a partial occupancy of the Na⁺ sites in the counter-cation–water system by Gd³⁺ ions (0.33 Gd³⁺ ions in total).     

Catalytic gold nanoparticles for fluorescent detection of mercury(II) and lead(II) ions

In this study, we developed a fluorescence assay for the highly sensitive and selective detection of Hg²⁺ and Pb²⁺ ions using a gold nanoparticle (Au NP)-based probe. The Hg–Au and Pb–Au alloys that formed on the Au NP surfaces allowed the Au NPs to exhibit peroxidase-mimicking catalytic activity in the H₂O₂-mediated oxidation of Amplex UltraRed (AUR). The fluorescence of the AUR oxidation product increased upon increasing the concentration of either Hg²⁺ or Pb²⁺ ions. By controlling the pH values of 5 mM tris–acetate buffers at 7.0 and 9.0, this H₂O₂–AUR–Au NP probe detected Hg²⁺ and Pb²⁺ ions, respectively, both with limits of detection (signal-to-noise ratio: 3) of 4.0 nM. The fluorescence intensity of the AUR oxidation product was proportional to the concentrations of Hg²⁺ and Pb²⁺ ions over ranges 0.05–1 μM (R² = 0.993) and 0.05–5 μM (R² = 0.996), respectively. The H₂O₂–AUR–Au NP probe was highly selective for Hg²⁺ (>100-fold) and Pb²⁺ (>300-fold) ions in the presence of other tested metal ions. We validated the practicality of this simple, selective, and sensitive H₂O₂–AUR–Au NP probe through determination of the concentrations of Hg²⁺ and Pb²⁺ ions in a lake water sample and of Pb²⁺ ions in a blood sample. To the best of our knowledge, this system is the first example of Au NPs being used as enzyme-mimics for the fluorescence detection of Hg²⁺ and Pb²⁺ ions.