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In the present work, we report the effect of the addition of platinum (Pt loading 1 wt%) on photocatalysts based on TiO2 and its incorporation in a SiO2 matrix using the sol gel method. The photocatalyst/silica matrix ratio was w(TiO2)/w(SiO2) of 15/85. The characterization of the samples was carried out with X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), specific surface area by N2 physisorption (BET) and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). The photoactivity of the samples was evaluated in the photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The production of hydroxyl radicals (•OH) on the surface of the samples irradiated with UV light was detected by the fluorescence technique using terephthalic acid as a test molecule. The resulting supported catalyst showed enhanced photocatalytic activity towards 2,4-D degradation, almost 97% of the 2, 4-D was degraded with Pt/TiM–Si sample in 180 min compared to pure commercial TiO2 P25 under UV radiation. The increase in photoactivity can be attributed to the extended band gap energy, large surface area, and a better charge separation and more efficient transfer of the photogenerated charges (e−–h+) due to the presence of Pt ions on the surface of the photocatalyst. Finally, stability and reusability test of the samples was estimated using recycling experiments, indicating its remarkable efficiency in contaminated water treatment.

Hybrid Ag/CeO2/SBA-15 mesoporous nanocatalysts were prepared and their bactericidal activity was evaluated aiming at elimination of Escherichia coli (E. coli) in the potable water system. It was found that there existed electrons transferring from Ag0 to CeO2 to form Ag+/Ag0 and Ce4+/Ce3+ couples in the heterojunction structure, which resulted from strong interaction between Ag nanoparticles (AgNPs) and highly dispersed CeO2. By increasing the Ag content from 1wt% to 3 and 5 wt% in the catalysts, the bactericidal power of Ag/CeO2/SBA-15 materials significantly enhanced in the presence of both visible and UV light, which can be explained by the increasing electrons transferring function from Ag0 to CeO2 under UV-visible light irradiation. A combination mechanism of E. coli deactivation was proposed where E. coli body may be simultaneously attacked by both AgNPs and Ag+ ions promoted by CeO2. The former may attack the cell membrane, leading to its cleavage and disruption; and the latter may be ionized and released from AgNPs to enter inside the cell, modifying its permeability and respiration, finally resulting in complete deactivation and death.

Highly active Fe3+ doped TiO2 (xFe–TiO2 where x = 3 or 5 wt%) photocatalysts were synthesized by the sol–gel method and their structures were refined with the Rietveld method. Several important effects of calcination temperature on the crystalline structure, textural features, phase concentration, Fe3+ distribution, optical properties, and photocatalytic activity were determined. When Fe–TiO2 materials were calcined at 400 °C, most of Fe3+ were formed α-Fe2O3 and some of them were incorporated in the network of TiO2 anatase; as calcination temperature increased to 800 °C, α-Fe2O3 and FeTiO3 coexisted on the TiO2 rutile phase. High calcination temperature also led to surface area sharply diminishing and the surface oxygen reducibility significantly decreasing. The interatomic distances of Fe–TiO2 catalysts obtained from the method of radial distribution function (RDF) were: Ti…O = 1.93 A (anatase), Fe…O = 2.59 A, Ti…Ti = 3.08 A, Ti…Fe = 3.69 A, Ti…Ti = 3.79 A, Ti…O = 4.83 A (rutile). In the photooxidation of 2,4-dichlorophenoxyacetic acid (2,4-DA), the photocatalytic activity of Fe–TiO2 catalyst increased with increase of Fe3+ content in anatase phase. The 2,4-DA photooxidation followed the first-order kinetic reaction model and favored under acidic condition. Approximately 95% 2,4–DA were photooxidized with the best catalyst 5Fe–TiO2–400 after 120 min of reaction under UV irradiation. TiO2 phase transformation from anatase to rutile and FeTiO3 formation at 800 °C negatively impacted on the photocatalytic performance. The catalytic activity of the catalysts correlated well with variations of textural properties, phase concentration, and surface oxygen reducibility that were all controlled by the calcination temperature.

Ti-MCM-41 supported vanadia core–shell catalysts were prepared and their catalytic activity was evaluated in a biphasic reactor for simultaneous oxidation/separation of refractory organosulfur compounds (dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT)) in a model diesel fuel. Formation of core–shell structure in the catalyst nanoparticles resulted from the surface diffusion of the vanadium ion in semimelted state of vanadia during the calcination process. It was found that both the value of V5+/(V4+ + V5+) and the surface acidity of the catalysts generally increased as the content of V content increased to 15 wt % of vanadium and correlated well with variations in catalytic activity, indicating that the surface V5+ and surface acid sites were chiefly responsible for the oxidation of sulfur compounds. The reactivity of organosulfur compounds was influenced by their steric hindrance. Addition of carboxylic acid (acetic acid or formic acid) promoted the...

A series of FeOx/Ti-MCM-41 mesostructured catalysts were synthesized and characterized by the X-ray diffraction (XRD), N2 adsorption-desorption isotherms, transmission electron microscopy (TEM), and Mossbauer spectroscopy. The surface reducibility and acidity of the catalysts were measured by temperature-programmed reduction of hydrogen (TPR-H2) and temperature-programmed desorption of ammonia (TPR-NH3) methods. Incorporating Ti4+ in the MCM-41 framework and loading Fe2O3 in the surface of the catalysts would create the acid sites and enhance the surface oxygen reducibility. Most of Fe3+ ions were highly dispersed on the surface and some were inserted into the framework of the support with different structural environments. The amount of the Fe3+ ions locating around the structural defects increased as the Fe content increased. In a biphasic reaction system (n-hexadecane/acetonitrile), the oxidation/elimination of dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) could correlate perfectly with the surface acidity and the amount of iron ions around the structural defects of the catalysts. The reactivity of sulfur compounds decreased with increasing of the steric hindrance, showing an order as: DBT > 4-MDBT > 4,6-DMDBT. In the presence of catalyst and oxidant, the polar/non-polar biphasic reaction system developed herein could effectively oxidize the sterically hindered sulfur compounds and simultaneously extracted the produced sulfones from oil phase into polar phase.

Double modifications of TiO2 by doping with WO3 and by dispersing on a SiO2 support were made by the one-pot sol-gel method. Doping with W shifts the TiO2 band gap energy from 3.2 eV to around 3.06 eV. The surface area of the supported W-TiO2/SiO2 material was significantly increased, by approximately 3 times, in comparison to the bare TiO2. The photocatalytic activities of the catalysts were evaluated in the degradation reaction of p-nitrophenol in aqueous solution and basic medium. After 240 min of photodegradation, more than approximately 99% p-nitrophenol could be mineralized with the most active W-TiO2/SiO2 catalyst. Under UV irradiation, p-nitrophenol was initially photodegraded into hydroquinone and benzosemiquinone intermediates, which were further degraded into smaller fragments such as organic carboxylic acids and finally completely mineralized. A proposed photoreaction mechanism was presented based on the key roles of the surface hydroxyl species and superoxide radicals such as O2- and ⋅OH, together with W6+/W5+ couples and e-/h+ pairs in the catalysts in the p-nitrophenol photodegradation. The one-pot sol-gel synthesis method was proven to be effective to obtain W-TiO2/SiO2 catalyst with large surface area and high photocatalytic activity, and it can be also used for the preparation of other heterogeneous catalysts.

A series of CuO supported on graphite carbon catalysts (noted as Cu/GC) was prepared with impregnation method and CuO loading varied from 1 wt% to 5, 10 and 15 wt%. Textural properties, crystalline structure, phase composition, copper oxidation states, and morphology of the Cu/GC catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy. Surface acidity was measured by using temperature-programmed desorption of ammonia (TPD-NH3). Surface Cu2+ ions, H2O2 oxidant, acetic acid promoter, and acidic media were all crucial for oxidative desulfurization (ODS) of a model diesel fuel. Both XRD and XPS results confirmed that Cu2+ and Cu+ coexisted on the carbon surface and the Cu2+/(Cu2+ + Cu+) ratio increased with increasing of copper oxide loading. The copper speciation result is in good correlation with the catalytic activity, indicating that surface Cu2+ ions are the active catalytic sites. Acetic acid reacted with H2O2 to form surface peroxyacetic species that coordinated with Cu2+ on the Cu/GC catalysts in acidic media and promoted the ODS activity. Low pH condition favored significantly dibenzothiophene (DBT) oxidation. Under the optimal operation condition (pH = 0, reaction temperature 70 °C, and catalyst loading 0.3 g with H2O2-glacial acetic acid), DBT concentration in oil was reduced from an initial value of 300 ppm to 78 ppm, 9 ppm, 3 ppm and 0 ppm after ODS treatment using Cu/GC catalysts loading with 1, 5, 10, and 15 wt% of CuO, respectively.

Fe TiO 2 catalysts were synthesized with the sol–gel method and were characterized by X-ray diffraction, N 2 adsorption measurement, Mossbauer spectroscopy, UV–vis spectroscopy, Raman spectroscopy, temperature programmed reduction, and temperature programmed desorption of NH 3 . The Fe TiO 2 catalysts chiefly consist of crystalline anatase. Fe 3+ ions are highly dispersed on the surface and distributed in octahedral-coordinate sites within different environments in TiO 2 . The Fe TiO 2 catalysts were then evaluated for oxidation desulfurization of dibenzothiophene in a biphasic reaction mixture consisting of an acidified polar phase and a hexadecane model fuel phase. Compared to control tests, the catalytic activity for dibenzothiophene (DBT) oxidation is markedly improved by addition of acetic acid, typically at least doubling DBT conversion compared to that observed under control conditions. Under optimal conditions (10 wt% Fe in the Fe TiO 2 catalyst and a pH adjusted to 0), 100% of the 300 ppm DBT initially present in the reaction mixture could be completely oxidized within 5 min. Oxidation of DBT formed sulfoxide/sulfones which were found to be enriched in the polar phase. The sol–gel Fe TiO 2 catalysts possess several attributes which may contribute to their activity for DBT oxidation: (1) their hydrophilic–hydrophobic character that facilitates DBT oxidation as a phase transfer catalyst; (2) coordination and activation of acetic acid and peroxyacetic acid with Fe 3+ and Ti 4+ present at the Fe TiO 2 surface, and (3) formation of superoxides at the Fe TiO 2 surface.

In this paper, we prepared by the sol–gel method alkaline titania catalysts, doped by gelling titanium alkoxide with aqueous solutions containing potassium, rubidium or cesium chlorides. XRD patterns showed that samples annealed at 400 and 600 °C contained a single crystalline phase, anastase. Specific surface areas were higher in samples annealed at 400 °C (>100 m2/g) than in those annealed at 600 °C (25 m2/g). The weight density of basic sites determined by CO2–TPD drastically diminished in samples treated at 600 °C. Catalysts were tested for the self-condensation of acetone at 300 °C; main reaction products were isomesityl oxide, mesityl oxide and mesitylene. Samples annealed at 600 °C showed lower acetone conversion rate and low formation of mesitylene than that obtained on samples annealed at 400 °C. It is proposed that the formation of mesitylene occurs via the Michael reaction over the titania support.

The vapor-phase condensation of acetone was studied over TiO2-doped with 1 wt% of alkaline metals (Li, Na, K and Cs). The reaction was catalyzed by basic sites and the main products were mesityl oxide (MO), isomesityl oxide (ISMO) and mesitylene (M); other compounds as isophorone (IP) and phorone (P) were also obtained. The basic properties of the samples were determined by chemisorption of carbon dioxide. It was found that the number of the basic sites of the TiO2-doped catalysts increased in the following order: Li/TiO2 > Na/TiO2 ∼ K/TiO2 > Cs/TiO2; in contrast, the trend of the basic strength and total activity was Cs/TiO2 > K/TiO2 ∼ Na/TiO2 Li/TiO2. On the other hand, the selectivity patterns showed that the higher formation of MO was obtained with the catalyst which showed the lowest basic force (Li/TiO2). A direct correlation between the activity and the alkaline metal atomic radius was found, while the inverse dependence for the selectivity to mesityl oxide was observed.

Mesoporous and microporous silica substrates, each of these kinds endowed with unique textural characteristics, have been prepared via sol–gel and micelle-templating techniques and characterized through N 2 sorption. Materials consisting of a lattice of cage-like monodisperse cavities interconnected by narrow throats (SBA-16), a set of individual cylindrical pores of about the same size (SBA-15), a network of long sinuous ganglion-like sequences of bulges and throats (mesoporous glass, MG), or microporous arrangements of globular nanoparticles (microporous SiO 2 ) have been developed. The N 2 sorption isotherms of microporous silica at 76 K correspond to International Union of Pure and Applied Chemistry (IUPAC) type I, while those of mesoporous SBA-16, SBA-15, and MG silica match a type IV with hysteresis loops of types H1 or H2 depending on the regularity and nature of the void elements constituting the substrate. A characteristic common to all kinds of porous SiO 2 solids herein synthesized is the rigidity of the arrangements, since the total pore volumes attain limiting values. Pore-size distributions of mesoporous SiO 2 materials can be calculated by density functional theory (DFT) and sometimes by Barrett–Joyner–Halenda (BJH) methods. The microporous SiO 2 adsorbent depicts a larger amount of big micropores (supermicropores) rather than small micropores (ultramicropores), this being a very useful characteristic for the entrapment and ulterior release of volatile compounds. MG substrates depict a percolation vapor threshold while the SBA-16 material shows a cavitation phenomenon during capillary evaporation. Additional properties of SBA-16, SBA-15, MG silica substrates are studied via primary desorption scanning curves.

TG, FTIR-(CO absorption), and catalytic activity in the NO reduction by CO were used to characterize Cu/Al2O3-TiO2 catalysts prepared by co-gelling aluminum tri-sec-butoxide and titanium iso-propoxide at pH 9 and at pH 3 gelling conditions. Under nitrogen flow, copper oxide decomposition, oxygen storage capacity (OSC) and sample dehydroxylation (total mass loss) was followed by TG. The CuO decomposition forming Cu0, Cu+1 was observed by means of FTIR (CO absorption) spectra. In pH 9 sample the large amount of Cu0 was observed. At low total mass loss and high Cu0/Cu+1+Cu+2 ratio (pH 9 sample) a lowest light-off in the NO reduction by CO was observed.

Ru/SiO 2 , Cu/SiO 2 and Cu–Ru/SiO 2 catalysts containing 1% wt. of the active metal on the silica support were prepared in various ways and characterized by appropriate spectroscopic techniques. FTIR results show that the hydroxyl ions of the support is stable up at 800°C. Thermal treatment of samples does not modify BET areas, in the range of 600 m 2 /g, nor the values of the average size of the metallic particles. The study of the catalytic activity using the phenylacetylene hydrogenation test reaction shows that the Ru/SiO 2 catalysts have high activity and selectivity to styrene. However, when Cu is additionally impregnated into these solids, no activity is observed in the test reaction of hydrogenolysis of n -heptane. Finally, all catalysts show good activity in the reduction of NO x by CO.

Silica samples were prepared by the sol–gel process varying the hydrolysis catalyst. The samples were characterized by X-ray diffraction and the radial distribution function was determined (R.D.F.). Fourier transform infrared spectroscopy and thermal analysis were also used. It was found that OH-retention capacity as well as order in the material may be modified with hydrolysis catalysts. When the hydrolysis catalyst was NH 4 OH the sample did not dehydroxylate even at 1000°C.

Aluminosilicates were prepared by the sol−gel method using tetraethoxysilane as silica source and aluminum ethoxide, aluminum iso-propoxide, or aluminum sec-butoxide as alumina sources. An importan...

Platinum SiO 2 sonogel has been compared with the corresponding xerogel and an impregnated catalyst. The thermal behavior, the FTIR spectra and the pyridine adsorption show that Lewis acidity is present in the impregnated sample. In the sonogel, Lewis acidity turns to be very low and insensitive to desorption temperature. In the xerogel, both Lewis and Bronsted acidity was observed. In each sample, reduction in situ (without hydrogen flow) of the metal phase is determined by the OH content. Platinum is highly reduced in the sonogel, partially reduced in the xerogel and very slightly reduced in the impregnated sample.

Alumina supported platinum-tin catalysts were synthesized using the sol-gel method. The solids were characterized by TGA and DTA analyses. It was found that the catalysts remain hydroxylated after having been thermally stabilized. Moreover, when under a hydrogen flux, Pt reduces producing an intense exothermic peak at room temperature.

Pt-Sn supported catalysts were prepared by the sol-gel method. The solids were characterized by FTIR and UV-VIS spectroscopy and N2 adsorption analysis. The platinum showed a deformed octahedral symmetry, tending to come to the surface as metallic platinum and forming small particles anchored to the support.

Impregnation and sol-gel preparation methods are compared. Only when prepared by sol-gel synthesis, ruthenium is incorporated in the silica network; RuO2 particles are observed, but most Ru is occluded in the silica network. The ruthenium migrates to the surface with thermal treatments and small particles are formed. In the case of impregnated catalysts only RuO2 particles are observed. Their diameter is larger when the catalyst is treated at high temperatures, ortho-Xylene hydrogenation was performed on these two kinds of catalysts. The deactivation and selectivity values are attributed to the structural differences of the catalysts. © 1992 Academic Press, Inc.

Platinum on silica catalysts have been prepared by adding [PtCl 6 ] -2 to tetraethoxysilane (TEOS). After hydrolysis and condensation a gel is formed. The addition of platinum into the gel has an important effect on the surface area of the solid (up to 1,100 m 2 m/g). The catalysts with a low metal concentration (≤0.5 wt%) are active for the hydrogenation of alkenes but not for the hydrogenation of aromatics. A support effect can be proposed to explain the low activity for benzene and ortho-xylene hydrogenation

The present study reports the results obtained by UV-VIS spectroscopy, FT-IR (Fourier transform infrared) spectroscopy, and BET area measurements of Pd/SiO2 catalysts synthesized by the sol-gel process. This preparation technique results in the hydrolysis and polycondensation of a silicon alkoxide, which contains the metal halide salt PdCl2 in the initial solution. The reaction takes place at pH 9, forming intermediates which correspond most probably to surface species [SiO2]-[PdClxOHy]-OH The interaction between the silica gel and the palladium precursor has important effects on the specific surface area. The products are solids with BET specific areas up to 800 m2/g. Catalytic tests (hydrogenation of 1-hexene and phenylacetylene) show that sol-gel catalysts exhibit high selectivity in the formation of 2-methylpentane and styrene. To explain the high selectivities shown by the Pd sol-gel catalysts a geometric effect induced by the support is proposed on the structure of the ca. 1-nm-size Pd metal particles.

Impregnation and sol-gel preparation methods are compared. Only when prepared by sol-gel synthesis, ruthenium is incorporated in the silica network; RuO2 particles are observed, but most Ru is occluded in the silica network. The ruthenium migrates to the surface with thermal treatments and small particles are formed. In the case of impregnated catalysts only RuO2 particles are observed. Their diameter is larger when the catalyst is treated at high temperatures, ortho-Xylene hydrogenation was performed on these two kinds of catalysts. The deactivation and selectivity values are attributed to the structural differences of the catalysts. © 1992 Academic Press, Inc.

Silico-aluminates were synthesized from aluminum and silicon alkoxides by the sol-gel method and characterized by FTIR spectroscopy. The water and alumina concentration effects in specific BET areas and activity in isopropanol dehydration were studied. High specific BET areas were found and a correlation between the tetrahedral coordination and selectivity as well as deactivation is proposed.

Homogeneous single phase sol-gels of magnesia and alumina were prepared using magnesium and aluminum alkoxides as precursors. The gels were formed through a hydrolysis reactions followed by condensation. These materials behave as basic catalysts and, therefore, are superb anionic interchangers. The solids obtained were characterized by infrared spectroscopy, thermogravimetric analysis and anionic interchange tests. No evidence for the presence of the individual binary oxides was found. An important effect on the dehydroxylation of the surface and on the anionic exchange was found as a function of alumina content in the magnesia matrix. The best sample was the one containing 50% MgO-50% Al2O3.

Ultrasound can be used in sol-gel synthesis as a source of energy which may modify the structural and chemical properties of the resulting gels. Pt/SiO 2 sonogel catalysts were obtained and characterized by X-ray diffraction and small angle X-ray scattering. It was found that the aging and polymerization mechanisms are altered by ultrasound. The catalysts were then tested in phenylacetylene hydrogenation, showing a high selectivity toward styrene.