A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4P... more A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4PW11V1O40 and TBA5PW10V2O40) and Mo (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS), and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)12−XO40)(3+X)− anions are the main species present in the TBA salts. Additionally, CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 at 170 °C. Independently of...
En este trabajo se reporta la preparacion de diferentes peliculas a base de quitosano conteniendo... more En este trabajo se reporta la preparacion de diferentes peliculas a base de quitosano conteniendo diferentes cargas de titania modificada con acido tungstofosforico (TiO2-TPA), este ultimo con capacidad de absorber luz visible entre 400 y 500 nm. Estas peliculas fueron caracterizadas por SEM, EDAX, DRX, angulo de contacto (CA) y ATR-FT-IR, encontrandose que las nanoparticulas de TiO2-TPA se encuentran altamente dispersas en las peliculas de quitosano (QTiO2-TPA) y que la interaccion entre estas y los grupos funcionales del quitosano son debiles.
Se sintetizo y caracterizo el heteropolioxotungstovanadato [N(prop)4]4[PVW11O40] (PVN) el cual fu... more Se sintetizo y caracterizo el heteropolioxotungstovanadato [N(prop)4]4[PVW11O40] (PVN) el cual fue inmovilizado en un polimero superabsorbente (POL) modificado utilizando una plantilla esferica de silice como formadora de poros. El catalizador preparado presento estructura tipo Keggin, gran area superficial y estabilidad termica alta. El mismo fue empleado en la oxidacion selectiva de difenil sulfuro, una reaccion de interes tanto a nivel industrial como en investigacion basica debido al amplio campo de aplicacion de este tipo de compuestos. Pudo obtenerse de manera selectiva el sulfoxido y la sulfona correspondiente bajo ciertas condiciones de reaccion y mediante un proceso eco-compatible.
Fil: Gomez, Silvina del Valle. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro... more Fil: Gomez, Silvina del Valle. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Centro de Investigacion y Tecnologia Quimica; Argentina
Se sintetizaron catalizadores (SNX#WPA) basados en ácido tungstofosfórico, en soportes de nanoest... more Se sintetizaron catalizadores (SNX#WPA) basados en ácido tungstofosfórico, en soportes de nanoestructuras de sílice (SNX), con distribución de diámetros y tamaños de mesoporos variables. Las SNX se prepararon en medio de octano/agua, usando poliestireno y bromuro de cetiltrimetilamonio como plantillas. Los materiales se caracterizaron por DRX, TEM y adsorción/desorción de nitrógeno. La relación octano/agua influyó tanto en la morfología y el tamaño de las SNX como en la distribución del tamaño de poro. Las SNX obtenidas utilizando relaciones OCT/H2O en el rango de 0,07-0,35, presentan mesoporos pequeños (5-6 nm) y grandes (28-34 nm), generados principalmente por poliestireno. Los mesoporos grandes y su contribución de volumen fueron claramente más altos que en las muestras SN1, SN2 y SN3. La estructura y la morfología de SNX#WPA fueron similares a las de las SNX usadas como soporte. Además, la caracterización de todos los materiales SNX#WPA por FT-IR y 31P NMR indicó la presencia de...
Magnetic materials based on Keggin heteropolyacids immobilized on mesoporous silica-coated magnet... more Magnetic materials based on Keggin heteropolyacids immobilized on mesoporous silica-coated magnetite particles with a core-shell structure were synthesized. The activity of the catalyst was studied in the esterification reaction of levulinic acid with n-butanol, and its kinetics was studied by the systematic variation of several reaction parameters, such as stirring speed, catalyst loading, molar ratio of reactants, and temperature. It was also seen that the reaction was free from any external mass transfer as well as intraparticle diffusion limitations and was intrinsically kinetically controlled. A second-order kinetic equation was found to be consistent with the experimental data. Also, an experimental activation energy of 17 kcal/mol was found. A solvent-free condition for this reaction has also added the green chemistry perception to the reaction. In addition, the resulting catalyst can be used repeatedly without significant decrease in activity.
Degradation study of malachite green on chitosan films containing heterojunctions of melon/TiO 2 ... more Degradation study of malachite green on chitosan films containing heterojunctions of melon/TiO 2 absorbing visible-light in solid-gas interfaces
The Photo-Fenton-like (PF-like) process with minute Fe(III) concentrations and the Hydrogen Perox... more The Photo-Fenton-like (PF-like) process with minute Fe(III) concentrations and the Hydrogen Peroxide Photolysis (HPP), using Xe-lamp or solar light as sources of irradiation, were efficiently applied to eliminate the herbicide 2,4-D from water. PF-like experiments concerning ferric and HO concentrations of 0.6 mg L and 20 mg L respectively, using Xenon lamps (Xe-lamps) as a source of irradiation and 2,4-D concentrations of 10 mg L at pH 3.6, exhibited complete 2,4-D degradation and 77% dissolved organic carbon (DOC) removal after 30 min and 6 h of irradiation respectively whereas HPP (in absence of ferric ions) experiments showed a 2,4-D reduction and DOC removal of 90% and 7% respectively after 6 h of irradiation. At pH 7.0, HPP process achieved a 2,4-D abatement of approximately 75% and a DOC removal of 4% after 6 h. PF-like exhibited slightly improved 2,4-D and DOC removals (80% and 12% respectively) after the same irradiation time probably due to the low pH reduction (from 7.0 t...
Iron modified ZSM-11 zeolites were tested as heterogeneous catalysts in the photodegradation of D... more Iron modified ZSM-11 zeolites were tested as heterogeneous catalysts in the photodegradation of Dichlorvos water solutions. ZSM-11 zeolite matrixes were synthesized by the hydrothermal method and iron was incorporated by the wet impregnation method in four different concentrations. Catalysts samples were characterized by several techniques (XRD, BET, UV-vis DRS, ICP-OES, TPR, EPR) in order to confirm structure, crystallinity and iron species present. a-Fe 2 O 3 was detected by XRD in higher iron content samples and it presence was confirmed by EPR, TPR and UV-vis DRS. Band gap energies for Fe/ZSM-11 samples were closer to that reported for pure a-Fe 2 O 3. The materials so far characterized were tested as heterogeneous catalyst in Dichlorvos photodegradation. Fe/ZSM-11 with a 6 wt% of iron incorporation showed the best catalytic behavior. Higher iron loadings showed lower degradation efficiencies. This material is reusable for at least six catalytic cycles without considerable differences among the DDVP amount degraded.
Heteropolyacid (HPA) based catalysts were prepared by impregnation of silica and alumina with dim... more Heteropolyacid (HPA) based catalysts were prepared by impregnation of silica and alumina with dimethylformamide solutions of molybdophosphoric and tungstophosphoric acids. This solvent allows the preservation of the Keggin unit during the impregnation independently of the nature of the support. Ni-promoted catalysts were prepared by impregnation with nickel nitrate solutions of the supported HPA. The stronger interaction of the HPA with alumina than with silica allows a better dispersion of the polyoxometallate species on the former one whereas the formation of bulk oxides is observed on silica. The performance of these HPA-Ni/support catalysts for hydrodenitrogenation and hydrodesulfurization reactions is related to the precursor-support interaction.
Materials based on tungstophosphoric acid (TPA) immobilized on NH 4 ZSM5 zeolite were prepared by... more Materials based on tungstophosphoric acid (TPA) immobilized on NH 4 ZSM5 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 N 2 adsorption-desorption isotherms, XRD, FT-IR, 31 P MAS-NMR, TGA-DSC, DRS-UV-Vis, and the acidic behavior was studied by potentiometric titration with n-butylamine. The BET surface area (S BET) 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 NH 4 ZSM5 zeolites, and an additional set of peaks assigned to the presence of (NH 4) 3 PW 12 O 40. According to the Fourier transform infrared and 31 P magic angle spinning-nuclear magnetic resonance spectra, the main species present in the samples was the [PW 12 O 40 ] 3anion, which was partially transformed into the [P 2 W 21 O 71 ] 6anion during the synthesis and drying steps. The thermal stability of the NH 4 ZSM5TPA 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 TiO 2. The immobilization of TPA on NH 4 ZSM5 zeolite allowed the obtention of catalysts with high photocatalytic activity in the degradation of methyl orange dye (MO) in water, at 25 °C. These can be reused at least three times without any significant decrease in degree of degradation.
Polyoxometalates with lacunary Keggin structure modified with transition metal ions [PW 11 O 39 M... more Polyoxometalates with lacunary Keggin structure modified with transition metal ions [PW 11 O 39 M(H 2 O)] 5− , where M= Ni 2+ , Co 2+ , Cu 2+ or Zn 2+ , were synthesized and supported on activated carbon to obtain the PW11MC catalysts. Using FT-IR and DTA-TGA it was concluded that the [PW 11 O 39 M(H 2 O)] 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 H 2 O 2 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.
Materials based on titania supported on zeolitic matrices (HBETA, HY and HZSM5) were synthesized ... more Materials based on titania supported on zeolitic matrices (HBETA, HY and HZSM5) were synthesized by in situ generation of TiO 2. The supported catalysts characterized by XRD indicate the presence of the anatase phase alone. The materials were also characterized by FTIR, S BET , and UV-VIS DRS. A high TiO 2 content produced lower degradation, due to the presence of TiO 2 particle aggregates of greater size on the zeolite matrix surface, as evidenced by the calculated crystal size. TiO 2 /HBETA(20%) presented more activity than TiO 2 supported on the other matrices due to higher adsorption of dichlorvos on HBETA. It has more surface area and a lower band gap value too, which makes it more effective. The mineralization degree is lower than the degradation percentage due to the formation of organophosphorous intermediates that are less toxic than the starting material. The complete degradation and mineralization of the pollutant was obtained in 360 and 540 min of reaction with TiO 2 /HBETA(20%), respectively. This catalyst resulted in degradation percentages close to that of commercial TiO 2 P25. The main advantage of supported catalysts is their easy separation and reuse, in this case resulting in a very low activity loss during eight cycles. These materials present suitable properties to be used as catalysts in the photocatalytic treatment of wastewater that contains pesticide dichlorvos in water.
New tungsten complexes based on the tridentate ligand [O,N,O]-2-[(4-hydroxy-3-pentene-2-ylidene) ... more New tungsten complexes based on the tridentate ligand [O,N,O]-2-[(4-hydroxy-3-pentene-2-ylidene) amino]phenol (hpap) were synthesized by the direct ligation of the ligand to WOCl 4 , leading to the displacement of two chloride units from the metal center and the formation of cis and trans isomers of the corresponding dichloride complex. The molecular structure of cis-[WOCl 2-(hpap)] was verified by X-ray crystallography. The synthesized [WOCl 2-(hpap)], a mixture of both cis and trans isomers, has been demonstrated to form a highly active catalyst in the Ring Opening Metathesis Polymerization (ROMP) of cyclic olefins such as TCD and MCMT, in combination with trialkyl aluminum as a promoter. However, the effectiveness in the metathesis of polar substituted monomers was found to be slightly lower, which may be due to the interaction of monomer polar groups with the catalyst components. The chemical structure of the resulting ROMP'd poly-TCD was characterized using one and two-dimensional 1 H NMR and 13 C NMR spectroscopy.
Several stilbenes and styrenes have been treated with heteropolyacid] (HPA) supported over silice... more Several stilbenes and styrenes have been treated with heteropolyacid] (HPA) supported over silice. The compounds obtained were characterized by 1 H and 13 C-NMR and the yields were compared with those obtained using H 2 SO 4 (c) and ethyl poliphosphate] (PPE).
A layer-by-layer deposition strategy was employed for the immobilization of tungstophosphoric aci... more A layer-by-layer deposition strategy was employed for the immobilization of tungstophosphoric acid (HPW) onto a pentaethylenehexamine (PEHA)-grafted ZrSBA-15 framework to a give HPW/PEHA/ZrSBA-15 composite. The resulting composite was characterized by XRD, SEM, TEM, FTIR, thermogravimetric analysis, N 2 sorption, and X-ray photoelectron spectroscopy, and these methods showed that the composite was stable in polar environments. These properties were attributed to the method of preparation, which ensured that a dense and stable array of HPW was encapsulated
ABSTRACT Two series of materials based on tungstophosphoric acid (TPA) immobilized on NH4Y and NH... more ABSTRACT Two series of materials based on tungstophosphoric acid (TPA) immobilized on NH4Y and NH4ZSM5 zeolites 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 specific surface area (SBET) decreased when the TPA content was raised as a result of the zeolite pore blocking. The X-ray diffraction patterns of the solids modified with TPA only presented the characteristic peaks of NH4Y and 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 (except for NH4YTPA05) is the [PW12O40]3− anion, which was partially transformed into [P2W21O71]6− anion during the synthesis and drying steps. The thermal stability of the NH4YTPA and NH4ZSM5TPA materials is similar to that of their parent zeolites. Moreover, the samples with the higher TPA content present band gap energy values similar to those reported for TiO2.The immobilization of TPA on NH4Y and NH4ZSM5 zeolites is a good method to obtain catalysts with high photocatalytic activity in the 4-chlorophenol degradation. They can be reused at least three times without an important decrease in the degradation degrees.
The parabens, alkylic esters of p-hydroxybenzoic acid, were synthesized using trifluoromethanesul... more The parabens, alkylic esters of p-hydroxybenzoic acid, were synthesized using trifluoromethanesulfonic acid immobilized on zirconium oxide (zirconia) as catalyst. The oxide was obtained by the sol–gel method, using urea as a pore-forming agent. After removing urea by extraction with water, the solid was dried and then calcined at 100, 205, 310 and 425°C for 24h. Afterward, it was impregnated with
Tungstophosphoric acid (TPA) in 50% v/v ethanol±water solutions was used to impregnate carbon, Ti... more Tungstophosphoric acid (TPA) in 50% v/v ethanol±water solutions was used to impregnate carbon, TiO 2 , SiO 2 and-Al 2 O 3 (Spheralite and Akzo) at 208C. The solutions were characterized by UV-visible and nuclear magnetic resonance spectroscopies and the results indicated that the main species present was the undegraded anion of the acid both before and after the contact with carbon, TiO 2 , SiO 2 and-Al 2 O 3 Akzo. However, the nuclear magnetic resonance spectrum of the solution in contact with-Al 2 O 3 Spheralite allowed to observe a tungstodiphosphate anion. X-ray diffraction of the impregnated solids dried at 708C showed the same diffraction patterns as the supports, possibly owing to a high dispersion of non-crystalline species. The Fourier transform infrared and nuclear magnetic resonance spectroscopies of carbon, TiO 2 and SiO 2 impregnated with TPA showed that the species present was the undegraded [PW 12 O 40 ] 3À anion. When using carbon and TiO 2 , the supported acid was thermally stable up to 4258C, similarly to the bulk acid, whereas on SiO 2 support, the anion underwent partial degradation from 3658C onwards. In TPA-impregnated-Al 2 O 3 samples dried at 708C, diffuse re¯ectance and nuclear magnetic resonance spectroscopies allowed us to observe a partial degradation of the anion, the extent of which was not appreciably increased by the subsequent calcination. The speci®c activity of the catalysts in the isopropanol dehydration reaction showed that TPA supported on carbon, TiO 2 and SiO 2 present higher acidity than the bulk acid, unlike in alumina where the partially degraded species gave a lower acidity.
A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4P... more A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4PW11V1O40 and TBA5PW10V2O40) and Mo (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS), and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)12−XO40)(3+X)− anions are the main species present in the TBA salts. Additionally, CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 at 170 °C. Independently of...
En este trabajo se reporta la preparacion de diferentes peliculas a base de quitosano conteniendo... more En este trabajo se reporta la preparacion de diferentes peliculas a base de quitosano conteniendo diferentes cargas de titania modificada con acido tungstofosforico (TiO2-TPA), este ultimo con capacidad de absorber luz visible entre 400 y 500 nm. Estas peliculas fueron caracterizadas por SEM, EDAX, DRX, angulo de contacto (CA) y ATR-FT-IR, encontrandose que las nanoparticulas de TiO2-TPA se encuentran altamente dispersas en las peliculas de quitosano (QTiO2-TPA) y que la interaccion entre estas y los grupos funcionales del quitosano son debiles.
Se sintetizo y caracterizo el heteropolioxotungstovanadato [N(prop)4]4[PVW11O40] (PVN) el cual fu... more Se sintetizo y caracterizo el heteropolioxotungstovanadato [N(prop)4]4[PVW11O40] (PVN) el cual fue inmovilizado en un polimero superabsorbente (POL) modificado utilizando una plantilla esferica de silice como formadora de poros. El catalizador preparado presento estructura tipo Keggin, gran area superficial y estabilidad termica alta. El mismo fue empleado en la oxidacion selectiva de difenil sulfuro, una reaccion de interes tanto a nivel industrial como en investigacion basica debido al amplio campo de aplicacion de este tipo de compuestos. Pudo obtenerse de manera selectiva el sulfoxido y la sulfona correspondiente bajo ciertas condiciones de reaccion y mediante un proceso eco-compatible.
Fil: Gomez, Silvina del Valle. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro... more Fil: Gomez, Silvina del Valle. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Centro de Investigacion y Tecnologia Quimica; Argentina
Se sintetizaron catalizadores (SNX#WPA) basados en ácido tungstofosfórico, en soportes de nanoest... more Se sintetizaron catalizadores (SNX#WPA) basados en ácido tungstofosfórico, en soportes de nanoestructuras de sílice (SNX), con distribución de diámetros y tamaños de mesoporos variables. Las SNX se prepararon en medio de octano/agua, usando poliestireno y bromuro de cetiltrimetilamonio como plantillas. Los materiales se caracterizaron por DRX, TEM y adsorción/desorción de nitrógeno. La relación octano/agua influyó tanto en la morfología y el tamaño de las SNX como en la distribución del tamaño de poro. Las SNX obtenidas utilizando relaciones OCT/H2O en el rango de 0,07-0,35, presentan mesoporos pequeños (5-6 nm) y grandes (28-34 nm), generados principalmente por poliestireno. Los mesoporos grandes y su contribución de volumen fueron claramente más altos que en las muestras SN1, SN2 y SN3. La estructura y la morfología de SNX#WPA fueron similares a las de las SNX usadas como soporte. Además, la caracterización de todos los materiales SNX#WPA por FT-IR y 31P NMR indicó la presencia de...
Magnetic materials based on Keggin heteropolyacids immobilized on mesoporous silica-coated magnet... more Magnetic materials based on Keggin heteropolyacids immobilized on mesoporous silica-coated magnetite particles with a core-shell structure were synthesized. The activity of the catalyst was studied in the esterification reaction of levulinic acid with n-butanol, and its kinetics was studied by the systematic variation of several reaction parameters, such as stirring speed, catalyst loading, molar ratio of reactants, and temperature. It was also seen that the reaction was free from any external mass transfer as well as intraparticle diffusion limitations and was intrinsically kinetically controlled. A second-order kinetic equation was found to be consistent with the experimental data. Also, an experimental activation energy of 17 kcal/mol was found. A solvent-free condition for this reaction has also added the green chemistry perception to the reaction. In addition, the resulting catalyst can be used repeatedly without significant decrease in activity.
Degradation study of malachite green on chitosan films containing heterojunctions of melon/TiO 2 ... more Degradation study of malachite green on chitosan films containing heterojunctions of melon/TiO 2 absorbing visible-light in solid-gas interfaces
The Photo-Fenton-like (PF-like) process with minute Fe(III) concentrations and the Hydrogen Perox... more The Photo-Fenton-like (PF-like) process with minute Fe(III) concentrations and the Hydrogen Peroxide Photolysis (HPP), using Xe-lamp or solar light as sources of irradiation, were efficiently applied to eliminate the herbicide 2,4-D from water. PF-like experiments concerning ferric and HO concentrations of 0.6 mg L and 20 mg L respectively, using Xenon lamps (Xe-lamps) as a source of irradiation and 2,4-D concentrations of 10 mg L at pH 3.6, exhibited complete 2,4-D degradation and 77% dissolved organic carbon (DOC) removal after 30 min and 6 h of irradiation respectively whereas HPP (in absence of ferric ions) experiments showed a 2,4-D reduction and DOC removal of 90% and 7% respectively after 6 h of irradiation. At pH 7.0, HPP process achieved a 2,4-D abatement of approximately 75% and a DOC removal of 4% after 6 h. PF-like exhibited slightly improved 2,4-D and DOC removals (80% and 12% respectively) after the same irradiation time probably due to the low pH reduction (from 7.0 t...
Iron modified ZSM-11 zeolites were tested as heterogeneous catalysts in the photodegradation of D... more Iron modified ZSM-11 zeolites were tested as heterogeneous catalysts in the photodegradation of Dichlorvos water solutions. ZSM-11 zeolite matrixes were synthesized by the hydrothermal method and iron was incorporated by the wet impregnation method in four different concentrations. Catalysts samples were characterized by several techniques (XRD, BET, UV-vis DRS, ICP-OES, TPR, EPR) in order to confirm structure, crystallinity and iron species present. a-Fe 2 O 3 was detected by XRD in higher iron content samples and it presence was confirmed by EPR, TPR and UV-vis DRS. Band gap energies for Fe/ZSM-11 samples were closer to that reported for pure a-Fe 2 O 3. The materials so far characterized were tested as heterogeneous catalyst in Dichlorvos photodegradation. Fe/ZSM-11 with a 6 wt% of iron incorporation showed the best catalytic behavior. Higher iron loadings showed lower degradation efficiencies. This material is reusable for at least six catalytic cycles without considerable differences among the DDVP amount degraded.
Heteropolyacid (HPA) based catalysts were prepared by impregnation of silica and alumina with dim... more Heteropolyacid (HPA) based catalysts were prepared by impregnation of silica and alumina with dimethylformamide solutions of molybdophosphoric and tungstophosphoric acids. This solvent allows the preservation of the Keggin unit during the impregnation independently of the nature of the support. Ni-promoted catalysts were prepared by impregnation with nickel nitrate solutions of the supported HPA. The stronger interaction of the HPA with alumina than with silica allows a better dispersion of the polyoxometallate species on the former one whereas the formation of bulk oxides is observed on silica. The performance of these HPA-Ni/support catalysts for hydrodenitrogenation and hydrodesulfurization reactions is related to the precursor-support interaction.
Materials based on tungstophosphoric acid (TPA) immobilized on NH 4 ZSM5 zeolite were prepared by... more Materials based on tungstophosphoric acid (TPA) immobilized on NH 4 ZSM5 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 N 2 adsorption-desorption isotherms, XRD, FT-IR, 31 P MAS-NMR, TGA-DSC, DRS-UV-Vis, and the acidic behavior was studied by potentiometric titration with n-butylamine. The BET surface area (S BET) 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 NH 4 ZSM5 zeolites, and an additional set of peaks assigned to the presence of (NH 4) 3 PW 12 O 40. According to the Fourier transform infrared and 31 P magic angle spinning-nuclear magnetic resonance spectra, the main species present in the samples was the [PW 12 O 40 ] 3anion, which was partially transformed into the [P 2 W 21 O 71 ] 6anion during the synthesis and drying steps. The thermal stability of the NH 4 ZSM5TPA 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 TiO 2. The immobilization of TPA on NH 4 ZSM5 zeolite allowed the obtention of catalysts with high photocatalytic activity in the degradation of methyl orange dye (MO) in water, at 25 °C. These can be reused at least three times without any significant decrease in degree of degradation.
Polyoxometalates with lacunary Keggin structure modified with transition metal ions [PW 11 O 39 M... more Polyoxometalates with lacunary Keggin structure modified with transition metal ions [PW 11 O 39 M(H 2 O)] 5− , where M= Ni 2+ , Co 2+ , Cu 2+ or Zn 2+ , were synthesized and supported on activated carbon to obtain the PW11MC catalysts. Using FT-IR and DTA-TGA it was concluded that the [PW 11 O 39 M(H 2 O)] 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 H 2 O 2 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.
Materials based on titania supported on zeolitic matrices (HBETA, HY and HZSM5) were synthesized ... more Materials based on titania supported on zeolitic matrices (HBETA, HY and HZSM5) were synthesized by in situ generation of TiO 2. The supported catalysts characterized by XRD indicate the presence of the anatase phase alone. The materials were also characterized by FTIR, S BET , and UV-VIS DRS. A high TiO 2 content produced lower degradation, due to the presence of TiO 2 particle aggregates of greater size on the zeolite matrix surface, as evidenced by the calculated crystal size. TiO 2 /HBETA(20%) presented more activity than TiO 2 supported on the other matrices due to higher adsorption of dichlorvos on HBETA. It has more surface area and a lower band gap value too, which makes it more effective. The mineralization degree is lower than the degradation percentage due to the formation of organophosphorous intermediates that are less toxic than the starting material. The complete degradation and mineralization of the pollutant was obtained in 360 and 540 min of reaction with TiO 2 /HBETA(20%), respectively. This catalyst resulted in degradation percentages close to that of commercial TiO 2 P25. The main advantage of supported catalysts is their easy separation and reuse, in this case resulting in a very low activity loss during eight cycles. These materials present suitable properties to be used as catalysts in the photocatalytic treatment of wastewater that contains pesticide dichlorvos in water.
New tungsten complexes based on the tridentate ligand [O,N,O]-2-[(4-hydroxy-3-pentene-2-ylidene) ... more New tungsten complexes based on the tridentate ligand [O,N,O]-2-[(4-hydroxy-3-pentene-2-ylidene) amino]phenol (hpap) were synthesized by the direct ligation of the ligand to WOCl 4 , leading to the displacement of two chloride units from the metal center and the formation of cis and trans isomers of the corresponding dichloride complex. The molecular structure of cis-[WOCl 2-(hpap)] was verified by X-ray crystallography. The synthesized [WOCl 2-(hpap)], a mixture of both cis and trans isomers, has been demonstrated to form a highly active catalyst in the Ring Opening Metathesis Polymerization (ROMP) of cyclic olefins such as TCD and MCMT, in combination with trialkyl aluminum as a promoter. However, the effectiveness in the metathesis of polar substituted monomers was found to be slightly lower, which may be due to the interaction of monomer polar groups with the catalyst components. The chemical structure of the resulting ROMP'd poly-TCD was characterized using one and two-dimensional 1 H NMR and 13 C NMR spectroscopy.
Several stilbenes and styrenes have been treated with heteropolyacid] (HPA) supported over silice... more Several stilbenes and styrenes have been treated with heteropolyacid] (HPA) supported over silice. The compounds obtained were characterized by 1 H and 13 C-NMR and the yields were compared with those obtained using H 2 SO 4 (c) and ethyl poliphosphate] (PPE).
A layer-by-layer deposition strategy was employed for the immobilization of tungstophosphoric aci... more A layer-by-layer deposition strategy was employed for the immobilization of tungstophosphoric acid (HPW) onto a pentaethylenehexamine (PEHA)-grafted ZrSBA-15 framework to a give HPW/PEHA/ZrSBA-15 composite. The resulting composite was characterized by XRD, SEM, TEM, FTIR, thermogravimetric analysis, N 2 sorption, and X-ray photoelectron spectroscopy, and these methods showed that the composite was stable in polar environments. These properties were attributed to the method of preparation, which ensured that a dense and stable array of HPW was encapsulated
ABSTRACT Two series of materials based on tungstophosphoric acid (TPA) immobilized on NH4Y and NH... more ABSTRACT Two series of materials based on tungstophosphoric acid (TPA) immobilized on NH4Y and NH4ZSM5 zeolites 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 specific surface area (SBET) decreased when the TPA content was raised as a result of the zeolite pore blocking. The X-ray diffraction patterns of the solids modified with TPA only presented the characteristic peaks of NH4Y and 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 (except for NH4YTPA05) is the [PW12O40]3− anion, which was partially transformed into [P2W21O71]6− anion during the synthesis and drying steps. The thermal stability of the NH4YTPA and NH4ZSM5TPA materials is similar to that of their parent zeolites. Moreover, the samples with the higher TPA content present band gap energy values similar to those reported for TiO2.The immobilization of TPA on NH4Y and NH4ZSM5 zeolites is a good method to obtain catalysts with high photocatalytic activity in the 4-chlorophenol degradation. They can be reused at least three times without an important decrease in the degradation degrees.
The parabens, alkylic esters of p-hydroxybenzoic acid, were synthesized using trifluoromethanesul... more The parabens, alkylic esters of p-hydroxybenzoic acid, were synthesized using trifluoromethanesulfonic acid immobilized on zirconium oxide (zirconia) as catalyst. The oxide was obtained by the sol–gel method, using urea as a pore-forming agent. After removing urea by extraction with water, the solid was dried and then calcined at 100, 205, 310 and 425°C for 24h. Afterward, it was impregnated with
Tungstophosphoric acid (TPA) in 50% v/v ethanol±water solutions was used to impregnate carbon, Ti... more Tungstophosphoric acid (TPA) in 50% v/v ethanol±water solutions was used to impregnate carbon, TiO 2 , SiO 2 and-Al 2 O 3 (Spheralite and Akzo) at 208C. The solutions were characterized by UV-visible and nuclear magnetic resonance spectroscopies and the results indicated that the main species present was the undegraded anion of the acid both before and after the contact with carbon, TiO 2 , SiO 2 and-Al 2 O 3 Akzo. However, the nuclear magnetic resonance spectrum of the solution in contact with-Al 2 O 3 Spheralite allowed to observe a tungstodiphosphate anion. X-ray diffraction of the impregnated solids dried at 708C showed the same diffraction patterns as the supports, possibly owing to a high dispersion of non-crystalline species. The Fourier transform infrared and nuclear magnetic resonance spectroscopies of carbon, TiO 2 and SiO 2 impregnated with TPA showed that the species present was the undegraded [PW 12 O 40 ] 3À anion. When using carbon and TiO 2 , the supported acid was thermally stable up to 4258C, similarly to the bulk acid, whereas on SiO 2 support, the anion underwent partial degradation from 3658C onwards. In TPA-impregnated-Al 2 O 3 samples dried at 708C, diffuse re¯ectance and nuclear magnetic resonance spectroscopies allowed us to observe a partial degradation of the anion, the extent of which was not appreciably increased by the subsequent calcination. The speci®c activity of the catalysts in the isopropanol dehydration reaction showed that TPA supported on carbon, TiO 2 and SiO 2 present higher acidity than the bulk acid, unlike in alumina where the partially degraded species gave a lower acidity.
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Papers by Luis Pizzio