Alkylation of hydroquinone with methyl-tert-butyl-ether and tert-butanol

The alkylation of hydroquinone yields industrially important compounds, amongst which tert-butylhydroquinone is a very important precursor for its use in pharmaceuticals and in developing photographic plates. Twenty per cent (w/w) dodecatungstophosphoric acid supported on K10 montmorillonite clay (DTP/K10) was found to be a very efficient and novel catalyst in comparison with several others for alkylation of hydroquinone with different alkylating agents such as methyl-tert-butyl-ether (MTBE) and tert-butanol at 150°C in an autoclave. A summary of characterisation of DTP/K10 is provided and related to the activity. Various reaction parameters were also investigated and a kinetic model was built. The rate of alkylation with MTBE was much faster than that with tert-butanol. The reaction follows a typical second order kinetics at a fixed catalyst loading with weak adsorption of both the species. The energy of activation was found to be 19.34 kcal/mol.     

A Novel Glass Membrane for Low Temperature H2/O2 Fuel Cell Electrolytes

A novel structure for an H₂/O₂ fuel cell with a proton conducting glass electrolyte and a Pt/C catalyst was developed. The performance of the fuel cell, which was impregnated with a glass electrolyte and a gaseous hydrogen–oxygen feed at low temperature in a humidified atmosphere was significantly improved by introducing membrane electrode assemblies (MEAs) consisting of heteropolyacids (HPAs) (phosphotungstic acid, PWA and phosphomolybdic acid, PMA) doped with a P₂O₅‐SiO₂ glass electrolyte. The HPAs containing porous glass electrolytes show promise for applications in low temperature H₂/O₂ fuel cells. The electrochemical behaviour of these materials was studied by measuring the current–voltage profile from polarisation curves. A maximum power density of ≈ 35 mW cm^–2 was obtained at 30 °C and 30% RH (relative humidity) using a PMA/PWA‐P₂O₅‐SiO₂ glass electrolyte membrane. The impedance measurements displaying the total cell ohmic resistance for 12 h at 0.5 V were evaluated at 30 °C. The resistance value was 3.5 Ω for an operating time of 12 h. This MEA showed the best and the most stable performance for use in an H₂/O₂ fuel cell.     

Preparation and characterisation of chemisorbents based on heteropolyacids supported on synthetic mesoporous carbons and silica

The preparation of chemisorbents based on tungsto- and molybdophosphoric acids supported on two types of synthetic mesoporous carbons and two types of mesoporous silica is described. Strong solid acids with good accessibility to acid sites may potentially be effective adsorbents for the removal of basic molecular impurities, such as amines, from ultrapure manufacturing environments. Prepared materials were characterised by scanning electron microscopy, nitrogen adsorption, Fourier-transform infrared spectroscopy, powder X-ray diffraction, and equilibrium ammonia uptake. Composites of SBA-15 with heteropolyacids were synthesised. It was shown that the inclusion of HPAs into SBA-15 results in the loss of long range order. Adsorbents based on the HPAs impregnated into the supports with the open-pore morphology (Novacarb and SBA-15) were found to be promising materials. A composite of tungstophosphoric acid with sol–gel SiO₂ was found to have the highest ammonia uptake.     

Influence of microporosity of activated carbons as a support of polyoxometalates

H₃[PMo₁₂O₄₀] (PMo) was supported on four activated carbons (AC) in order to analyze the influence that the porous texture of AC exercises in the adsorption of PMo, trying to study where they are adsorbed and how their adsorption modifies the porous texture of AC. The amount of PMo adsorbed on AC follows a clear correlation with the porous texture, microporosity being the best evidence for this. Such a correlation indicates that PMo is only adsorbed in supermicroporosity as a consequence of the size of PMo, which limits the entrance on the smallest micropores, about 0.8 nm. XRD results indicate that the PMo is adsorbed on the micropore wall, that it is highly dispersed and that it does not develop any crystalline phase.     

Phosphotungstic acid supported on magnetic core–shell nanoparticles with high photocatalytic activity

Fe₃O₄@SiO₂@HPW (12-tungstophosphoric acid) nanoparticles have been successfully obtained by a simple solvothermal and impregnation process. The as-obtained products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectrum (FT-IR), inductively coupled plasma (ICP) and MPM5-XL-5 superconducting quantum interference device (SQUID). The results revealed that the heteropolyacids were successfully grown on the Fe₃O₄@SiO₂ nanoparticles. The photocatalytic studies suggested that the Fe₃O₄@SiO₂@HPW nanoparticles show excellent photocatalytic efficiency for the degradation of Rhodamine B (RB) under UV light irradiation. More importantly, the obtained nanoparticles (Fe₃O₄@SiO₂@HPW) could be effectively separated for reuse by simply applying an external magnetic field. Furthermore, the synthesized nanoparticles could keep their efficiency till four cycles.     

Homogeneous borotungstic acid and heterogeneous micellar borotungstic acid catalysts for biodiesel production by esterification of free fatty acid

A highly negatively charged borotungstic acid H₅BW₁₂O₄₀ had been tested as homogeneous catalyst in esterification. Compared with common used H₃PW₁₂O₄₀, it displayed a higher conversion (98.7%) and excellent efficiency (96.2%) due to its high amount of protons in methanol. In order to overcome the drawbacks of homogeneous heteropolyacid H₅BW₁₂O₄₀, a Brønsted-surfactant-combined (C₁₆TA)H₄BW₁₂O₄₀ (C₁₆TA = cetyltrimethyl ammonium) had been fabricated with strong acidity and nano-size micellar structure resulting in enhanced activity and stability during the reaction, which exhibited consistent activity during recycling in esterification reaction.     

Hydrocracking of Fischer‐Tropsch Wax with Tungstovanadophosphoric Salts as Catalysts

The synthesis of liquid hydrocarbons from CO₂ and H₂, based on renewable energy and H₂O electrolysis, respectively, in a power‐to‐liquid process is a promising concept for the substitution of fossil fuels. Such a process is based on Fischer‐Tropsch synthesis followed by hydrocracking to convert waxy products into transportation fuels such as gasoline and diesel oil. Heteropolyacid cesium salts as catalysts show appropriate activity for hydrocracking, and the selectivity in cracking model hydrocarbons and Fischer‐Tropsch wax can be tuned by the vanadium content of the catalyst. Thermal stability and surface properties were investigated, and the catalysts are compared with a classical H‐Y‐type zeolite used for hydrocracking.     

Effects of Brønsted and Lewis Acidities on Catalytic Activity of Heteropolyacids in Transesterification and Esterification Reactions

Some salts of H₃PW₁₂O₄₀‐M_x/nH_3–xPW₁₂O₄₀ (abbreviated as M_x/nH_3–xPW) were prepared and used as acid catalysts for transesterification and esterification reactions. These catalysts have double acidity properties, i.e., Lewis acidity and Brønsted acidity, that are suitable for the conversion of waste cooking oil into biodiesel. The highest efficiency was 59.2 % and 94.7 % corresponding to transesterification and esterification reactions by Ti_0.6H_0.6PW with moderate Lewis acidity. The relationship between the acidic properties and the catalytic activity is discussed in detail.     

Studies in structural characterization of silica–heteropolyacids composites prepared by sol–gel method

Heteropolyacids (HPAs) which are included in mesoporous silica, H₃PMo₁₂O₄₀/SiO₂ and H₄PMo₁₁VO₄₀/SiO₂ have been synthesized by a sol–gel technique that involves hydrolysis of ethyl orthosilicate. The effect of incorporation of heteropolyacids species on silica matrix was studied by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopy, thermo gravimetric analysis (TGA) and differential thermal analysis (DTA), N₂ adsorption–desorption, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).     

Hydration of α-pinene over molybdophosphoric acid immobilized in hydrophobically modified PVA membranes

A polyvinylalcohol/molybdophosphoric acid (PVA/HPMo) membrane crosslinked with succinic acid was modified by treatment with acetic anhydride in order to improve its hydrophobic properties, and was used as catalyst in the hydration reaction of α-pinene. The increase of membrane hydrophobicity with acetylation is documented not only by the water droplet contact angle but also by the sorption coefficients of α-pinene and water. The introduction of acetyl groups improves the membrane transport properties, as reflected by pinene diffusivity calculated from permeation data.A kinetic-diffusion model was developed assuming that the reaction product α-terpineol affects the transport of water and α-pinene across the acetylated PVA membranes. When membrane acetylation increases, the model predicted kinetic constants for hydration and isomerization reactions decrease, although the initial water diffusivity increases. These results suggest that the increase of catalytic activity may be due to an improvement of water transport across the membrane.