Effect of promoters for n-butane oxidation to maleic anhydride over vanadium–phosphorus‐oxide catalysts: comparison with supported vanadia catalysts

The oxidation of n-butane to maleic anhydride was investigated over model Nb‐, Si‐, Ti‐, V‐, and Zr‐promoted bulk VPO and supported vanadia catalysts. The promoters were concentrated in the surface region of the bulk VPO catalysts. For the supported vanadia catalysts, the vanadia phase was present as a two‐dimensional metal oxide overlayer on the different oxide supports (TiO₂, ZrO₂, Nb₂O₅, Al₂O₃, and SiO₂). No correlation was found between the electronegativity of the promoter or oxide support cation and the catalytic properties of these two catalytic systems. The maleic anhydride selectivity correlated with the Lewis acidity of the promoter cations and oxide supports. Both promoted bulk VPO and supported vanadia catalysts containing surface niobia species were the most active and selective to maleic anhydride. These findings suggest that the activation of n-butane on both the bulk and supported vanadia catalysts probably requires both surface redox and acid sites, and that the acidity also plays an important role in controlling further kinetic steps of n-butane oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation and characterisation of diopside-based glass–ceramic foams

Foaming and crystallisation behaviours of compacted glass powders based on a diopside glass–ceramic composition were investigated using the sintering route. The foaming agent was 2 wt.% SiC particles. The effect of PbO on the foaming ability of glasses was investigated. The results showed that the addition of PbO not only improved the foaming ability, by improving the wettability of the glass–SiC particles but also increased the crystallisation temperature and widened the temperature interval between the dilatometric softening point and the onset of crystallisation. The glass–SiC wetting angle was decreased from 85° for the lead-free glass, to 55° for the glass that contains 15 wt.% PbO.     

Electron microscopy studies of vanadium phosphorus oxide catalysts derived from VOPO4·2H2O

An electron microscopy study of vanadium phosphorus oxide (VPO) catalysts is reported. The catalyst precursor VOHPO₄·0.5H₂O was prepared from VOPO₄·2H₂O using isobutanol as the reducing agent. The catalyst was then fully activated by heating for ca. 75 h under reaction conditions (385C, GHSV 1000 h^–1, 1.5% butane in air). Scanning electron microscopy studies demonstrated that a topotactic transformation occurs between the precursor and the final catalyst. Transmission electron microscopy experiments revealed that there were three distinctive morphologies present in the final catalyst; namely (i) rosette shaped clusters composed of (VO)₂P₂O₇ crystallites, (ii) crystalline platelets of _II-VOPO₄ and (iii) disordered platelets exhibiting surface patches of (VO)₂P₂O₇. This latter morphology corresponds to the disordered remnants of hemihydrate particles which have only partially transformed to (VO)₂P₂O₇. The (VO)₂P₂O₇ platelets were found to be the majority phase making up more than 95% of the volume fraction.     

Preparation and use of hybrid organic–inorganic catalysts

Various approaches towards the immobilization of molecular homogeneous catalysts are introduced, focusing on catalysts where an organic molecule is attached to the surface of an inorganic support material via a covalent bond forming the so-called hybrid organic–inorganic catalysts. The application of this new class of catalysts in a wide variety of organic reactions is reviewed.     

Preparation and phosphorus recovery performance of porous calcium–silicate–hydrate

Porous calcium–silicate–hydrate was synthesized and used to recover phosphorus from wastewater. The principal objective of this study was to explore the phosphorus recovery performance of porous calcium–silicate–hydrate prepared by different Ca/Si molar ratios. Phosphorus recovery mechanism was also investigated via Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectrum (EDS), Brunauer–Emmett–Teller (BET) and X-ray Diffraction (XRD). The law of Ca²⁺ release was the key of phosphorus recovery performance. Different Ca/Si molar ratios resulted in the changes of pore structures. The increase of specific surface area and the increase in concentration of Ca²⁺ release were well agreement together. The Ca/Si molar ratio of 1.6 for porous calcium–silicate–hydrate is more proper to recover phosphorus. The pore structure of porous calcium–silicate–hydrate provided a local condition to maintain a high concentration of Ca²⁺ release. Porous calcium–silicate–hydrate could release a proper concentration of Ca²⁺ and OH^? to maintain the pH values at 8.5–9.5. This condition was beneficial to the formation of hydroxyapatite. Phosphorus content of porous calcium–silicate–hydrate reached 18.64% after phosphorus recovery.     

Preparation and structural characterisation of a novel ferrocene–amino acid conjugate

A new type of ferrocene–amino acid conjugate, 2-[(methoxycarbonyl)methyl]-2-aza[3]ferrocenophane (1), was obtained in a rather low yield via condensation reaction of 1,1′-bis(hydroxymethyl)ferrocene and glycine methyl ester in the presence of [RuCl₂(PPh₃)₃] as a catalyst. The compound was characterised by combustion analysis and by spectroscopic method, and its solid-state structure was established by single-crystal X-ray diffraction analysis. Compound 1 is reluctant towards alkylation with MeI but readily forms a stable picrate salt. Cyclic voltammetry experiments on 1 (in CH₃CN at Pt electrode) revealed the compound to undergo a one-electron reversible oxidation attributable to ferrocene/ferrocenium couple (E^o′ = ?5 mV vs. ferrocene itself), which shifts towards more positive potentials upon protonation with HCl.     

Preparation and characterisation of α-methylstyrene–butadiene latexes for paper coating applications

The purpose of this work is to demonstrate how α-methylstyrene (AMS) can replace styrene in preparing styrene–butadiene (SB) type latexes and to compare the properties of the paper coating of the prepared α-methylstyrene–butadiene emulsion with the commercial styrene–butadiene latex reference sample. A lot of work is nowadays being conducted on different biorefinery concepts replacing fossil oil with biomass based raw materials due to the expected rise of the fossil oil cost. Aromatics can in principle be produced from renewable raw materials, such as lignin, sugars and terpenes for example. The potential methods include thermochemical conversions, catalytic fast pyrolysis, metabolic engineering, catalytic aromatisation and dehydrogenation among others. Terpenes, such as α-limonene and pinene, are possible sources of aromatics, and they can indeed be catalytically converted to p-cymene. Industrial hydrodealkylation and disproportionation processes developed by major petrochemical companies can further convert p-cymene to BTX aromatics or simultaneously dehydrogenate the alkyl chain of p-cymene to styrenic monomers such as α-methylstyrene. Based on the measured paper properties for uncalendered and calendered coated samples, AMS proved to be adequate to replace the oil based styrene in commercial reference SB latexes. Even though the emulsion polymerisation for the α-methylstyrene–butadiene latex was not optimised, almost all tested properties were at least equally good as in the commercial reference sample. α-Methylstyrene containing coating colours had slightly higher viscosity than the other coating colours. Coating colours containing α-methylstyrene seems to have an improved water retention compared to the commercial reference styrene–butadiene latex coating colour and the laboratory prepared styrene–butadiene coating colour. The paper coated with the commercial reference latex containing coating colour was less porous than the other coated papers. Despite of that, both dry and wet surface strength were at least equally good as in the case of the commercial reference latex. The results are promising when thinking of the future development of the bio-based latexes.     

Adsorption and reaction of CO on vanadium oxide–Pd(111) “inverse” model catalysts: an HREELS study

The room temperature adsorption and reaction of CO on Pd(111) surfaces decorated with submonolayer coverages of vanadium oxide – so-called inverse model catalysts – have been studied by high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The HREELS surface phonon spectra of the V oxide phases have been measured and used to monitor the changes in the oxide as a result of the interaction with CO. The intramolecular C–O stretching frequency of CO adsorbed on the V-oxide/Pd(111) surfaces displays two vibrational loss components as a function of CO coverage as it has been observed on the clean Pd(111) surface. The relative intensities of the two vibrational features as a function of V oxide coverage however suggest that the balance of CO adsorption sites is modified as compared to clean Pd(111) by the presence of the V oxide–Pd phase boundary. Preferential population of high coordination adsorption sites by CO in the vicinity of the oxide–metal interface is proposed. The analysis of the V oxide phonon spectra indicates that adsorbed CO partially reduces the V oxide at the boundaries of the oxide islands to the Pd metal. The reduction of V oxide by CO is dependent on the oxygen content of the V oxide phase. The reduction of V oxide is confirmed by the XPS V 2p core level shifts.     

Thermal and combustion behavior of phosphorus–nitrogen and phosphorus–silicon retarded epoxy

A novel trizine ring-based phosphorus–nitrogen flame retardant, 1,3,5-tris(3-(diphenylphosphoryl)propyl)-1,3,5-triazinane-2,4,6-trione (PN), was synthesized by the reaction of diphenylphosphine oxide and triallyl isocyanurate with triethylborane as catalyst. Chemical structure of the target compound was confirmed by Flourier transform infrared spectrum, nuclear magnetic resonances, matrix-assisted laser desorption/ionization time-of-flight mass spectrum measurements. The newly developed PN was used in the flame retardancy of o-cresol novolac epoxy/phenolic novolac hardener system. For comparison, another analogous phosphorus–silicon flame retardant, [(1,1,3,3-tetramethyl-1,3-disiloxanediyl)-di-2,1-ethanediyl]-bis(diphenylphosphine oxide) (PSi), was also applied in the same system. Experimental results revealed that PN showed superior flame retardant efficiency to that of PSi. In addition, the incorporation of flame retardants was in favor of the char formation during the thermal degradation process of epoxy thermosets. With the same flame retardant content, the char residue of epoxy thermosets with PSi was higher than that of epoxy thermosets with PN at 750 °C. Cone calorimeter results indicated that PN contributed to gas phase flame retardancy while PSi was more likely to take part in flame retardancy in the condense phase. X-ray photoelectron spectroscopy data revealed that the binding energies of phosphorus changed in different ways in PN and PSi after combustion. This implied that phosphorus exhibited different combustion behaviors when combined with nitrogen or silicon.     

Oxidation of butane over vanadium–phosphorus oxides of P/V≥2

Two mixed oxides of vanadium and phosphorus, with phosphorus to vanadium atomic ratio (P/V) about 2 and 2.4, were studied as catalysts for selective oxidation of butane to maleic anhydride. The sample with P/V about 2 was poorly crystalline, contained a small amount of V(V), and oxidized butane to maleic anhydride with about 50% selectivity. The sample with P/V about 2.4 contained well crystalline VO(PO₃)₂ phase, but it deactivated with time-on-stream with the formation of V(PO₃)₃. The results suggested that the two samples differed greatly in their rates of oxidation of the vanadium ions.     

Low metal–insulator transition temperature of Ni-doped vanadium oxide films

Elemental doping is the main means to regulate the phase transition of vanadium oxide (VO₂); however, the effects of low valence elemental (<4+) doping on the phase transition of VO₂ are still controversial. In the present work, Ni-doped VO₂ films were prepared on quartz glass by direct current reactive magnetron sputtering and subsequent annealing. With the increase of the Ni doping content, the phase transition temperature of heating (T_H) of the VO₂ films decreased from 73.4 °C to 52.4 °C. The temperature required for the occurrence of phase transition (T_b) was lower than T_MIT. Different from the undoped VO₂ film, the Ni-doped VO₂ films had a T_b of around 30 °C. XRD and Raman results revealed that some rutile VO₂ microcrystals appeared in the vanadium oxide films because of the lattice distortion by incorporated Ni. Hence, rutile VO₂ micro-crystallinities significantly facilitated the phase transition of monoclinic VO₂ to rutile one.     

Preparation and characterisation of TiN by microwave-assisted carbothermic reduction–nitridation in air atmosphere

Titanium nitride (TiN) is prepared from ilmenite (FeTiO₃) powders by microwave-assisted carbothermic reduction–nitridation in air atmosphere followed by acid leaching treatment. The thermal analysis of the reduction–nitridation of FeTiO₃ powders is conducted by thermogravimetry/differential scanning calorimeter. The phase transition sequence of microwave carbothermal synthesis of TiN–Fe composite is: FeTiO₃?→?Fe?+?TiO₂?→?Fe?+?TiN. There is no any other oxygen-deficient titanium oxides detected. Particularly, FeTiO₃ can be transformed into TiN–Fe composite completely at 900°C for 60?min by microwave heating. The increase in both the reaction temperature and dwelling time is in favour of the transformation of FeTiO₃. The product morphologies are spherical about 2–5?μm in size. Then TiN is obtained with the removal of Fe and their oxides from TiN–Fe composite by acid leaching treatment. This method not only reduces the reaction temperature significantly through microwave heating but also can simplify the operation process effectively.     

Preparation and characterization of aluminum oxide–poly(ethylene-co-butyl acrylate) nanocomposites

This article describes the preparation and characterization of composites containing poly(ethylene-co-butyl acrylate) (EBA–13 and EBA–28 with 13 and 28 wt % butyl acrylate, respectively) and 2–12 wt % (0.5–3 vol %) of aluminum oxide nanoparticles (two types differing in specific surface area and hydroxyl-group concentration; uncoated and coated with, respectively, octyltriethoxysilane and aminopropyltriethoxysilane). A greater surface coverage was obtained with aminopropyltriethoxysilane than with octyltriethoxysilane. An overall good dispersion was obtained in the EBA-13 composites prepared by extrusion compounding. Composites with octyltriethoxysilane-coated nanoparticles showed the best dispersion. The addition of the nanoparticles to EBA–28 resulted in poor dispersion, probably due to insufficiently high shear forces acting during extrusion mixing which were unable to break down nanoparticle agglomerates. The nanoparticles had no effect on the crystallization kinetics in the EBA–13 composites, but in the EBA–28 composites the presence of the nanoparticles led to an increase in the crystallization peak temperature, suggesting that the nanoparticles had a nucleating effect in this particular polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Physico-chemical and catalytic properties of Mg–Al hydrotalcite and Mg–Al mixed oxide supported copper catalysts

The Mg–Al hydrotalcite (HT) and Mg–Al mixed oxide supported copper catalysts containing 3–3.5 wt.% copper in finely dispersed form were synthesized and characterized. The effect of support nature on physico-chemical and catalytic properties of supported copper species were studied. The loading of copper on the supports was observed to be influencing the surface acidic, basic and reducibility properties, and catalytic behavior in dehydrogenation of benzyl alcohol. The high basicity and intercalated copper ions in Mg–Al hydrotalcite supported copper sample showed multifunctional activity in catalytic transformations of alcohols (primary, secondary and aromatic alcohols).     

Preparation and catalytic activity in ethanol combustion reaction of cobalt–iron spinel catalysts

Iron–cobalt spinel catalysts were prepared via the coprecipitation method. The effect of different parameters on textural, structural and catalytic properties, in ethanol combustion, was investigated. The CoFe₂O₄ phase was obtained at calcination temperatures as low as 500 °C and the usage of ammonia as precipitating agent, results in the formation of Fe₂O₃ in addition to the spinel phase. The catalyst prepared using nitrate salts, NaOH as precipitation agent and calcined at 600 °C had the best catalytic performance achieving ethanol complete oxidation at 271 °C.     

Alumina-supported manganese- and manganese–palladium oxide catalysts for VOCs combustion

Alumina-supported manganese- and palladium–manganese oxide catalysts were prepared and tested in the combustion of formaldehyde. Total combustion of formaldehyde/methanol was achieved at 220 °C over a 18.2% Mn/Al₂O₃ catalyst. This temperature decreased either to 90 or 80 upon adding 0.1% or 0.4% Pd, respectively, to the base 18.2% Mn/Al₂O₃ catalyst. The combined use of X-ray diffraction, temperature-programmed reduction and photoelectron spectroscopy (XPS) techniques revealed that a Mn⁴⁺/Mn³⁺ oxide(s) and PdO_x species are present on the surface of the fresh catalysts and remain along the catalytic reaction.     

Epoxidation of cyclooctene over mesoporous Ga,Ga–Nb,and Ga–Mo oxide catalysts

We demonstrate the epoxidation of cyclooctene to epoxycyclooctane over mesoporous Ga and mixed Ga–Nb and Ga–Mo oxides synthesized via self-assembly hydrothermal-assisted approach. These mesoporous catalysts displayed high epoxide selectivities at moderate cyclooctene conversions. Mesoporous Ga oxides with average particle sizes between 2 and 3 μm exhibited higher cyclooctene conversions, while larger particle sizes between ~ 4.5–6.5 μm showed lower conversions. The incorporation of Nb led to an increase in the acidity of the resultant Ga–Nb mixed oxides. These mesoporous Ga–Nb mixed oxides displayed 80–100% selectivity for the epoxide at conversion levels of cyclooctene in the 17 to 30% range. Finally, a mesoporous Ga–Mo oxide with molar composition of 35% Mo displayed the highest cyclooctene conversion of all mesoporous samples at 60 °C. The conversion of this sample was 41% with 100% selectivity.     

Electrometallurgical recovery of nickel and vanadium from spent desulphurization catalysts using an acidic leaching–electrolysis technique

Spent desulphurization catalysts are considered a major secondary source of valuable metals. The contents of nickel and vanadium present in these catalysts, accompanied by environmental rules, have attracted scientists to explore diverse options for their effective processing. The electrometallurgy recovery of Ni and V from the spent desulphurization Ni-Mo-V/Al₂O₃ catalyst is described in this study. Using flat plate graphite electrodes, the electrochemical deposition of Ni and V from spent catalyst in an acid solution (HNO₃/H₂SO₄) was investigated. By the central composite design of the response surface methodology, the effect of the operating factors was examined and optimized. At the ideal conditions of reaction temperatures of 84.0 and 42.0°C, electrolysis times of 5.6 and 4.4 h, liquid/solid ratios of 22.7 and 15.4 ml/g, and current densities of 229.0 and 255.6 A/m², respectively, the recovery efficiencies of Ni and V were 81.96% and 93.07%. The statistical analysis revealed that the expected data (R² = 0.9984 and R² = 0.9883) were in good agreement with the observed data (R² = 0.9984), with an average variation from experimental data of 0.78% and 0.65% for the optimum conditions of Ni and V recovery, respectively. It shows that the Ni and V nanoparticles deposited have a spherical form with purities of 84.39% and 90.76%, respectively. Because of its great efficiency and purity, the current study can provide a dependable procedure for extracting Ni and V from solid waste.     

Hydration of ethene over W–P mixed metal oxide catalysts

W–P mixed metal oxide catalysts are active and selective for the gas-phase hydration of ethene to ethanol. The activity and selectivity of this catalytic reaction depend on the W/P atomic ratio. However, ethene conversion slightly decreases at higher W/(W + P) atomic ratio. The selectivity for ethanol increases with the W/P atomic ratio and reaches the highest value (92%) at W_0.81P_0.19O_x. The W_0.81P_0.19O_x catalyst is less active than the conventional H₃PO₄/SiO₂ catalyst, but the activity is maintained for a long time without the supply of any catalyst components. The reaction temperature does not affect substantially the rate of ethene hydration over the W_0.81P_0.19O_x catalyst. The H₂O/ethene molar ratio of 0.4 is the most appropriate for both reaction rate and selectivity. The active species of W–P mixed metal oxide are amorphous. But there is Keggin structure of W–P oxide species (PW₁₂O₄₀ ³⁻) in the presence of steam. And the species are the active sites for the hydration of ethene, confirmed by in situ Raman spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.