Luis Rene Pizzio

Preparation and characterization of TiO2/HZSM-11 zeolite for photodegradation of dichlorvos in aqueous solution

The TiO2/HZSM-11 materials were synthesized using titanium isopropoxide as a TiO2 precursor and HZSM-11 a medium pore size zeolite with high thermal and chemical resistance as support. The amount of titanium isopropoxide was varied in order to obtain TiO2 concentrations of 3, 10, 20, 30 and 50 wt% in the final material. They were characterized by a series of complementary techniques: X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy (DRS), transmittance Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The surface area of the TiO2/HZSM-11 samples decreased with the increment of TiO2 loading. As result of the increment of the calcination temperature from 450 to 800°C an increase in the size of the anatase crystals was observed. However, the X-ray diffraction patterns of the solids only presented the characteristic peaks of the anatase phase. The catalytic activity of the materials in the photodegradation of Dichlorvos (DDVP) depended on the TiO2 amount the thermal treatment temperature. The sample containing 30% TiO2 calcined at 450°C showed the best catalytic performance and it can be reused without noticeable activity loss during at least four cycles. The catalytic performance was similar to that of the P25 Degussa used as a reference but its separation, recovery and reuse was easier.

Efficient Tetrahydropyranylation of Phenols and Alcohols Catalyzed by Supported Mo and W Keggin Heteropolyacids

Abstract The protection of phenols as tetrahydropyranyl acetals is studied using supported Keggin heteropolyacids as catalysts, specifically molybdophosphoric or tungstophosphoric acids supported on silica. Phenol tetrahydropyranyl acetals are obtained in short times at room temperature with excellent yields. Protection of alcohols is also performed under mild conditions using both supported heteropolyacids, with yields ranging between good and quantitative. The reactions are clean and their workup is very simple. The use of these solid catalysts allows replacing the usual soluble inorganic acids, contributing to waste reduction.

Transition metal-modified polyoxometalates supported on carbon as catalyst in 2-(methylthio)-benzothiazole sulfoxidation

AbstractPolyoxometalates with lacunary Keggin structure modified with transition metal ions [PW11O39 M(H2O)]5−, where M = Ni2+, Co2+, Cu2+ or Zn2+, were synthesized and supported on activated carbon to obtain the PW11MC catalysts. Using FT-IR and DTA-TGA it was concluded that the [PW11O39M(H2O)]5− species are interacting with the functional groups of the support, and that thermal treatment leads to the loss of the coordinatively bonded water molecules without any noticeable anion degradation. The activity and selectivity of the catalysts in the sulfoxidation reaction of 2-(methylthio)-benzothiazole, an emerging environmental pollutant, were evaluated. The reaction was carried out in acetonitrile as solvent using H2O2 35% p/v as a clean oxidant. The conversion values decreased in the following order: PW11NiC > PW11CuC > PW11CoC > PW11ZnC, with selectivity to sulfoxide higher than 69%. The catalyst could be reused without appreciable loss of the catalytic activity at least three times. The materials were found to be efficient and recyclable catalysts for 2-(methylthio)-benzothiazole sulfoxidation in order to obtain a more biodegradable product than the corresponding substrate. Graphical AbstractPolyoxometalates with lacunary Keggin structure-modified with transition metal ions [PW11O39M(H2O)]5-, where M= Ni2+, Co2+, Cu2+ or Zn2+, were synthesized and supported on activated carbon to obtain the PW11MC catalysts.

TUNGSTOPHOSPHORIC ACID HETEROGENIZED ONTO NH4ZSM5 AS AN EFFICIENT AND RECYCLABLE CATALYST FOR THE PHOTOCATALYTIC DEGRADATION OF DYES

Materials based on tungstophosphoric acid (TPA) immobilized on NH4ZSM5 zeolite were prepared by wet impregnation of the zeolite matrix with TPA aqueous solutions. Their concentration was varied in order to obtain TPA contents of 5%, 10%, 20%, and 30% w/w in the solid. The materials were characterized by N2 adsorption-desorption isotherms, XRD, FT-IR, 31P MAS-NMR, TGA-DSC, DRS-UV-Vis, and the acidic behavior was studied by potentiometric titration with n-butylamine. The BET surface area (SBET) decreased when the TPA content was raised as a result of zeolite pore blocking. The X-ray diffraction patterns of the solids modified with TPA only presented the characteristic peaks of NH4ZSM5 zeolites, and an additional set of peaks assigned to the presence of (NH4)3PW12O40. According to the Fourier transform infrared and 31P magic angle spinning-nuclear magnetic resonance spectra, the main species present in the samples was the [PW12O40]3- anion, which was partially transformed into the [P2W21O71]6- anion during the synthesis and drying steps. The thermal stability of the NH4ZSM5TPA materials was similar to that of their parent zeolites. Moreover, the samples with the highest TPA content exhibited band gap energy values similar to those reported for TiO2. The immobilization of TPA on NH4ZSM5 zeolite allowed the obtention of catalysts with high photocatalytic activity in the degradation of methyl orange dye (MO) in water, at 25 oC. These can be reused at least three times without any significant decrease in degree of degradation.

Hydrotreating catalysts on alumina, titania or zirconia from ethanol/water solutions of heteropolyacids

Abstract Supported PNiMo(W) catalysts for hydrodesulfurization and hydrodenitrogenation were prepared. Heteropolyacids were used as precursors and supported on alumina, titania and zirconia. The tungstophosphoric and molybdophosphoric acids showed a stable Keggin-type structure when the supports were zirconia and titania. However, the heteropolyacids on alumina were degraded during the drying and/or calcination of the impregnated samples. The, catalysts prepared, on alumina had the highest activity, in the order of commercial ones. The catalysts on titania, were more active than the samples supported on zirconia.

Synthesis and characterization of tungstophosphoric acid-modified mesoporous silica nanoparticles with tuneable diameter and pore size distribution

Mesoporous silica nanoparticles were prepared in aqueous/organic phase using cetyltrimethylammonium bromide and polystyrene as organic templates. The morphology and crystalline phase of the products were characterized by scanning electron microcopy, transmission electron microscopy, X-ray diffraction, small angle X-ray scattering, and N2 adsorption/desorption isotherm analysis. The octane/water ratio influenced the pore size distribution, the morphology and size of the nanospheres obtained. Transmission electron microscopy revealed that mesoporous silica nanoparticles with “blackberry-like structure” (MSN3, MSN4, MSN5, and MSN6 samples) were obtained using octane/water ratios in the range 0.007–0.35. They present small (in the range 5–6 nm) and large (in the range 28–34 nm) mesopores. Large mesopores were mainly generated by polystyrene, and their volume contribution was clearly higher than in the MSN1 and MSN2 samples. The structure and morphology of mesoporous silica nanoparticles solids impregnated with tungstophosphoric acid were similar to those of the mesoporous silica nanospheres used as support. In addition, the characterization of all the solids impregnated with tungstophosphoric acid by Fourier transform infrared and 31P nuclear magnetic resonance indicated the presence of undegraded [PW12O40]3− and [H3−XPW12O40](3−X)− species interacting electrostatically with the ≡Si–OH2+ groups, and by potentiometric titration the solids presented very strong acid sites. In summary, they are good candidates to be used in reactions catalyzed by acids, especially to obtain quinoxaline derivatives.Graphical Abstract

Polymer-immobilized aluminium or copper tungstophosphates and tungstosilicates as new catalysts in anisole acylation

New materials with spherical shape were obtained from aluminium or copper salts of tungstophosphoric and tungstosilicic acids immobilized in a polymeric blend prepared with polyvinyl alcohol and polyethylene glycol by the freeze-thawing method. It is observed that the salts retain the Keggin structure of the heteropolyanions during their synthesis and immobilization. There is an almost constant distribution of the salts along the sphere width when they are included in the PVA-PEG blend. Also, the immobilized salts present very strong acid sites. The catalytic activity in the anisole acylation of the immobilized aluminium salts was higher than that of the catalysts obtained from the copper salts.

Synthesis and characterization of tungstophosphoric acid-modified mesoporous sponge-like TUD-1 materials

AbstractMesoporous sponge-like siliceous materials (TUD-1) were synthesized using TEOS (tetraethylorthosilicate) as a precursor of silica and TEA (triethanolamine) as a mesostructure-directing agent. Different TEOS/TEA molar ratios and hydrotreatment times were used, and their influence on the textural and morphological properties of the solids was evaluated. They were characterized by transmission electron microscopy (TEM), X-ray diffraction, and N2 adsorption/desorption isotherm analysis. By changing the TEOS/TEA molar ratio, micro-mesoporous and mesoporous (with a narrow or wide pore size distribution) materials were obtained. The increment of hydrotreatment times increased the average pore size of TUD-1 and significantly reduced the specific surface area. TEM images showed that the solids were formed by agglomerates of rather spherical particles whose size increased with the increment of the TEA amount used. The structure and morphology of TUD-1 solids modified with tungstophosphoric acid (TPA) were similar to those of the mesoporous silica used as support. Their diffraction patterns did not display any of the characteristic peaks of TPA or its more common hydrates, suggesting that TPA was well dispersed on the support as a noncrystalline phase. In addition, the characterization of all the solids impregnated with TPA by FT-IR and 31P NMR indicated the presence of undegraded [PW12O40]3− and [H3−XPW12O40]X− species interacting electrostatically with the ≡Si–OH2+ groups, and by potentiometric titration it was estimated that the solids presented very strong acid sites. The TUD-1 solids modified with TPA gave excellent yield in the solvent-free synthesis of 2,4,5-triphenyl-1H-imidazole, without formation of by-products resulting from competitive reactions or decomposition products. In summary, they are good candidates to be used in multicomponent reactions catalyzed by acids. HighlightsTUD-1 materials were synthetized using different TEOS/TEA molar ratios and hydrotreatment times.Their influence on the textural and morphological properties was evaluated.The TUD-1 materials were impregnated with tungstophosphoric acid.They gave excellent yield in the in the solvent-free synthesis of 2,4,5-triphenyl-1H-imidazole.