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Catalytic and catalytic photo-assisted hydration of propene to 2-propanol in gas-solid regime at atmospheric pressure and 85°C were carried out by using the Keggin heteropolyacid (HPA) H3PW12O40 (PW12) supported on home prepared SiO2, WO3, TiO2 or N-doped TiO2. The HPA played the key role both in catalytic and photocatalytic reactions; however, the support strongly influenced the binary material performance. The contemporary presence of heat and UV light improved the activity of the (photo)catalysts. EPR (Electron Paramagnetic Resonance) has been used to understand the intimate mechanism underlying the photoactivity of the supported heteropolyacid and the role played by the support.

Heterogeneous photocatalysis is a sustainable technology mainly employed for water and air cleaning purposes. However, in the last two decades a lot of attention has been given to photocatalysis as an alternative route to be used in place of traditional industrial processes. The sustainability of photocatalysis mainly comes from the exploitation of renewable sources, such as solar light, and the possibility to avoid unsafe reagents/solvents and severe temperatures and pressures. In this chapter we give a critical presentation of some case studies concerning the use of heterogeneous photocatalysts, such as modified and bare TiO2, ZnO, ZnS, WO3, titanium silicalite, V2O5, polyoxometalates, CdS, CdSe, Bi2O3, PbBi2Nb2O9, PbBiO2Br and SrBi2Nb2O9, in organic synthetic paths. Given the huge number of studies, a selection has been made among reactions of synthetic significance and/or of industrial interest, such as for instance (poly)aromatic partial oxidation, hydration and oxidation of propene, reduction and alkylation reactions. Special attention was paid to selectivity issues, the influence of catalyst features on selectivity and the possible use of green organic solvents when water-insoluble species have to be converted.

Strontium titanate perovskite (SrTiO3) and analogous materials in which Y partially substitutes Sr have been prepared as basis to integrate Co in the structure. The Co inserrtion has been performed by wet impregnation or coprecipitation methods. The obtained powders have been physico-chemically characterized and tested as photocatalysts in the propene partial oxidation by using a solar simulating reactor. Correlation between photocatalytic performance and physicochemical characteristics of the different catalysts allows to assess a key role of local nanostructuring of CoOx sites on the selectivity and distribution of products.

General considerations on the differences and similarities between heterogeneous photocatalysis and thermal catalysis are presented. Some research papers are reviewed where a reaction has been carried out in the presence of an inorganic material used both as catalyst and photocatalyst. The existing literature often compares catalytic reactions undertaken with the contemporaneous presence of radiation, showing only that photocatalytic reactions can occur under milder experimental conditions and at much lower temperatures. Nevertheless, differences in mechanistic aspects, conversions and selectivities between catalytic and photocatalytic reactions should also be highlighted. These are due to various reasons, relating to the effects of the interaction of light with the solid surface, adsorption-desorption of species involved in the (photo)reactions, and activation energy.

Catalytic and photocatalytic tests for propene hydration to 2-propanol were successfully carried out by using binary materials obtained by supporting a Keggin or Wells-Dawson heteropolyacids via impregnation method to commercial SiO2 or TiO2. (Photo)catalytic hydration was studied in gas-solid regime by using a continuous (photo)reactor working at atmospheric pressure and 80 °C. The alcohol was the main product. The acidity of the cluster accounts for the catalytic role, whereas both the acidity of the cluster and the oxidant ability were responsible for the increase of the reaction rate of the photo-assisted catalytic reaction. Moreover, the presence of a photoactive semiconductor support showed a beneficial effect to enhance the reactivity of the binary material.

Catalytic and photocatalytic 2-propanol dehydration was carried out by using a supported Keggin heteropolyacid H3PW12O40 (PW12). Binary materials were prepared by impregnation and/or solvothermal treatment by using commercial supports: SiO2 (Mallinckrodt), TiO2 (Evonik P25) and multiwall carbon nanotubes (Sunnano) or home solvothermically prepared SiO2 and TiO2. All the materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM) coupled with EDX microanalysis, specific surface area measurements, diffuse reflectance spectroscopy (DRS), FTIR and Raman spectroscopy. (Photo)catalytic 2-propanol dehydration was studied in gas-solid regime by using a continuous (photo)reactor working at atmospheric pressure and 80 °C. FTIR spectra of the gas-phase over the PW12-support composites, where 2-propanol had been previously adsorbed, were recorded. Propene and diisopropyl ether were the main reaction products. For the continuous photo-assisted runs the reactor was also illuminated with UV light. The apparent activation energy of 2-propanol catalytic and photocatalytic dehydration was determined in the range 60–120 °C. The irradiance increased significantly the dehydration reaction rate. Important differences were observed between the different supported materials. The Keggin heteropolyacid species played a key role both for the catalytic and the photo-assisted catalytic reactions; in fact, the acidity of the cluster accounts for the catalytic role, whereas both the acidity of the cluster and the oxidant ability of PW12 were responsible for the increase of the reaction rate of the photo-assisted catalytic reaction. Moreover, the photo-generated electrons on the solid semiconductor conduction band can account for a further increase of the reaction rate, when the heteropolyacid was supported on TiO2. Formation of a pseudo-liquid phase played an important role to determine the (photo)activity.

Tra i più studiati poliossometallati (nanoagglomerati di ossigeno con metalli transizionali), figurano gli eteropoliacidi (EPA) che sono degli acidi inorganici forti con ben defin ite strutture molecolari. In funzione della loro geometria, essi vengono classificati come Keggin e Wells-Dawson. Gli (EPA) sono usati in catalisi omogenea ed eterogenea e funzionano anche come fotocatalizzatori, essenzialmente in sistemi omogenei. Questi materiali sono, inoltre, economici e non tossici.

Catalytic and photocatalytic tests for 2-propanol dehydration to propene were successfully carried out by using binary materials obtained by supporting a Keggin or Wells-Dawson heteropolyacids via impregnation method to commercial SiO2 or TiO2. (Photo)catalytic 2-propanol dehydration was studied in gas-solid regime by using a continuous (photo)reactor working at atmospheric pressure and 80 °C. Propene and diisopropyl ether were the main reaction products. For the continuous photo-assisted runs the reactor was also illuminated with UV light. The heteropolyacid species played a key role both for the catalytic and the photo-assisted catalytic reactions; indicating that the acidity of the cluster accounts for the catalytic role, whereas both the acidity of the cluster and the oxidant ability were responsible for the increase of the reaction rate of the photo-assisted catalytic reaction. Moreover, the presence of a photoactive semiconductor support showed a beneficial effect to enhance the reactivity of the binary material. The increasing of the 2-propanol concentration in the secondary structure of both PW12 and P2W18, i.e. in the pseudo-liquid phase, gave rise to an increase of the (photo)activity up to a maximum value above which a further absorption of the reagent cause a decrease. The apparent activation energy of 2-propanol of the catalytic and photocatalytic dehydration has been determined in the range 60-120 °C for all of the (photo)catalysts used.

The photoassisted oxidative transformation of the highly recalcitrant cyanuric acid was examined in the liquid−solid regime at pH 3 and natural pH 7.5 under UV irradiation in oxygen- and ozone-saturated ZnO suspensions using ZnO as a photomediator. Loss of cyanuric acid was assayed by HPLC UV absorption spectroscopy, whereas intermediates and final products were determined by HPLC ion chromatography (IC), by MS techniques using an electrospray ionization mass spectrometer operated in the negative-ion mode, and by FT-IR spectroscopy. Final reaction products were CO2 gas and NO3- ions. The measure of nitrate in solution quantified the degree of mineralization of the substrate; its concentration in solution was lower than indicated by the loss of cyanuric acid owing to adsorption of the latter to the ZnO surface. Some degree of corrosion of ZnO occurred as evidenced by the quantity of Zn2+ present in acidic and near-neutral aqueous media before and during the photoassisted process. The possible site(s) and m...

Polyoxometalates (POMs) are a wide class of discrete nanosized transition metal–oxygen clusters. The synthesis of POMs has received great interest not only because they present intriguing architectures but also because they have potential applications in catalysis, medicine, electrochemistry, materials design or models for self-assembling nanoscale systems. Recently, POMs have also been studied as green and cheap photocatalysts. The potentialities of POMs are attributed to their unique structural features; indeed, POMs are photostable and non-toxic, have oxygen-rich surfaces and excellent redox properties and possess photochemical characteristics similar to those of the semiconductor photocatalysts. Heteropolyacids (HPAs), including their anions, are a POM subclass. In this chapter their photocatalytic properties when they are immobilized on various supports are described citing a part of the existing literature.

Catalytic and photocatalytic tests for 2-propanol dehydration to propene were successfully carried out by using binary materials obtained by supporting a Keggin heteropolyacid H3PW12O40 (PW12) via impregnation method and/or solvothermal treatment. The supports used were commercial SiO2 (Mallinckrodt), TiO2 (Evonik P25) and multiwall carbon nanotubes (Sunnano) or home solvothermically prepared SiO2 and TiO2. (Photo)catalytic 2-propanol dehydration was studied in gas-solid regime by using a continuous (photo)reactor working at atmospheric pressure and 80 °C. the reaction was also studied by performing FTIR spectra of the gas-phase over the HPA-support composites, where the 2-propanol had been previously adsorbed. Propene and diisopropyl ether were the main reaction products. For the continuous photo-assisted runs the reactor was also illuminated with UV light. The Keggin heteropolyacid species played a key role both for the catalytic and the photo-assisted catalytic reactions; indicating that the acidity of the cluster accounts for the catalytic role, whereas both the acidity of the cluster and the oxidant ability of PW12 were responsible for the increase of the reaction rate of the photo-assisted catalytic reaction. Moreover, the presence of a photoactive semiconductor support showed a beneficial effect to enhance the reactivity of the binary material. The increasing of the 2-propanol concentration in the secondary structure of PW12, i.e. in the pseudo-liquid phase, gave rise to an increase of the (photo)activity up to a maximum value above which a further absorption of the reagent cause a decrease. The apparent activation energy of 2-propanol catalytic and photocatalytic dehydration, determined in the range 60-120 °C, decreased in the presence of light for all of the (photo)catalysts used.

Catalytic and photocatalytic 2-propanol dehydration was carried out by using a supported Keggin heteropolyacid H3PW12O40 (PW12). Binary materials were prepared by impregnation and/or solvothermal treatment by using commercial supports: SiO2 (Mallinckrodt), TiO2 (Evonik P25) and multiwall carbon nanotubes (Sunnano) or home solvothermically prepared SiO2 and TiO2. All the materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM) coupled with EDX microanalysis, specific surface area measurements, diffuse reflectance spectroscopy (DRS), FTIR and Raman spectroscopy. (Photo)catalytic 2-propanol dehydration was studied in gas-solid regime by using a continuous (photo)reactor working at atmospheric pressure and 80 °C. FTIR spectra of the gas-phase over the HPA-support composites, where 2-propanol had been previously adsorbed, were recorded. Propene and diisopropyl ether were the main reaction products. For the continuous photo-assisted runs the reactor was also illuminated with UV light. The apparent activation energy of 2-propanol catalytic and photocatalytic dehydration was determined in the range 60-120 °C. The irradiance increased significantly the dehydration reaction rate. Important differences were observed between the different supported materials. The Keggin heteropolyacid species played a key role both for the catalytic and the photo-assisted catalytic reactions; in fact, the acidity of the cluster accounts for the catalytic role, whereas both the acidity of the cluster and the oxidant ability of PW12 were responsible for the increase of the reaction rate of the photo-assisted catalytic reaction. Moreover, when the heteropolyacid was supported on TiO2 the photo-generated electrons on the solid semiconductor conduction band, can account for a further increase in the reaction rate. Formation of a pseudo-liquid phase played an important role to determine the (photo)activity.

Commercial and home prepared bare and Pt-supported TiO2 samples were used as the photocatalysts for the aqueous aerobic and anaerobic photo-conversion of glucose at ambient pressure and temperature. H2 and valuable chemicals were the obtained products. The home prepared samples resulted more active than the commercial ones

The present work deals with a short review of some applications of photocatalysis to green organic synthesis of valuable products in mild experimental conditions and in the presence of water as solvent.

Commercial and home prepared TiO2 samples were functionalized with a commercial Keggin heteropolyacid (HPA) H 3PW12O 40 (PW12) or with a hydrothermally home prepared K 7PW11O 39 salt (PW11). All the materials were characterized by specific surface area measurements (BET), XRD analyses, Raman, DRS along with SEM observations and they have been used for glucose photocatalytic conversion in an aqueous suspension. Different reaction extents and distribution of intermediate oxidation products were observed depending on the photocatalyst. Gluconic acid, arabinose, erythrose and formic acid were observed as oxidation products when bare TiO2 or HPA/TiO2 composite materials were used. Glucose isomerization to form fructose was also observed and in some runs traces of glucaric acid and glyceraldehyde were also found. The carbon mass balance was accomplished in the presence of the commercial Evonik P25 TiO2 powder and the composites where TiO2 was present, whereas the presence of the solvothermically prepared TiO2 gave rise to a carbon unbalance, due to strong adsorption of the products on the photocatalyst surface. No reactivity was observed in the presence of PW12 alone while PW11 induced only isomerization of the glucose.

This contribution gives an account of TiO2-based selective photocatalysis as a green synthetic tool for the production of organics. Some case studies of the most common transformations carried out by means of photocatalytic reactions are illustrated.

(Photo)catalytic propene hydration to 2-propanol and glycerol dehydration to acrolein were carried out by using Keggin heteropolyacids (HPAs) supported on TiO 2 . Binary materials have been prepared by impregnation of H 3 PW 12 O 40 , H 3 PMo 12 O 40 and H 4 SiW 12 O 40 , on TiO 2 Evonik P25. Moreover, a binary material consisting of H 4 SiW 12 O 40 and TiO 2 was prepared via a hydrothermal treatment and tested for the same reactions. All the materials were characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM) coupled with energy dispersive X-ray (EDX) measurements, diffuse reflectance spectroscopy (DRS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The supported Keggin HPA species played a key role both for the catalytic and for the photo-assisted catalytic reactions due to their strong acidity and ability to form strong oxidant species under UV irradiation.

Catalytic and catalytic photo-assisted dehydration of 2-propanol to form propene in gas-solid regime at atmospheric pressure and 80°C was carried out by using a Keggin heteropolyacid H3PW12O40 (PW12) supported on different oxides. Binary materials have been prepared by impregnation of PW12 on different commercial and home prepared supports (TiO2, SiO2 or carbon nanotubes). The supported Keggin PW12 species played a key role both for the catalytic and the photo-assisted catalytic reactions, due to their strong acidity and ability to form strong oxidant species under UV irradiation, respectively. The contemporary presence of heat and UV light improved the activity of almost all POM supported materials.

La disidratazione catalitica e fotocatalitica di 2-propanol a propilene è stata effettuata usando eteropoliacidi di Keggin H3PW12O40 (PW12) e Wells-Dawson H6P2W18O60 (P2W18). Sono stati utilizzati sia supportani che non. Materiali binari sono stati preparati per l'impregnazione degli eteropoliacidi su supporti commerciali: SiO2 (Aldrich) e TiO2 (Evonik P25). I materiali sono stati caratterizzati e la loro (foto) attività catalitica rispetto alla disidratazione 2-propanol evaluata in regime gas-solido utilizzando un reattore continuo a pressione atmosferica e un range di temperatura fra 60 e 120 ° C. Inoltre, per gli esperimenti fotoassititi il reattore è stato illuminato da un LED UV. Importanti differenze sono state osservate fra le attività catalitiche di entrambi eteropoliacidi. I Wells-Dawson erano più attivi dei Keggin cataliticamente che foto-cataliticamente. Le differenze sono state evidenziate dalla dispersione su SiO2, ma l'uso del TiO2 come supporto ha massimizzato l'attività, in particolare nel caso dei Wells-Dawson, soprattutto in presenza di irradiazione UV.

LaCoO3 perovskites substituted by Sr at the A site and/or by Fe at the B site have been prepared by the citrate method. Characterizations by several techniques, such as specific surface area (BET method), XRD, TPR, SEM, UV–vis in DRS mode, XPS and TGA analyses, have been performed. The so prepared La1−xSrxCo1−yFeyO3−δ perovskites are semiconductor materials showing band gap energy values from 1.9 to 3.2 eV. They displayed solar photocatalytic activity for the 2-propanol degradation in gas–solid regime. The photocatalytic results suggest that the perovskites containing Fe are less active and the activity decreases by increasing the Fe content, however the presence of iron avoids the catalyst deactivation. The best photocatalytic activity in the 2-propanol degradation was found for the sample La0.6Sr0.4CoO3−δ.

Photocatalytic conversion of glucose was carried out in aqueous suspensions in the presence of dfifferent commercial and home prepared TiO2 samples functionalized with a commercial heteropolyacid. Different reaction extents and distribution of intermediate oxidation products were observed depending on the photocatalyst.

Both commercial and home prepared (HP) TiO2 samples have been tested for the photocatalytic reduction of CO2. (HP) TiO2 powders were prepared by using TiCl4 or Ti(OC4H9)4 as the precursors to obtain HP1 and HP2 samples, respectively. Also HP Cu-loaded and SiO2 supported TiO2 powders were prepared. The HP samples were more active than the commercial ones for the photoreduction of CO2 with and without water vapour. HP1 produced mainly formaldehyde, HP2 principally methane. Acetaldehyde was found to be the primary product obtained when HP1 was supported on SiO2. The addition of Cu increased the photocatalytic reactivity either of bulk and SiO2-supported HP1. In particular, 1 wt % of Cu improved the formaldehyde yield obtained with the bare HP1 by one order of magnitude. Differently, the presence of Cu or SiO2 in the HP2 samples markedly reduced the production of methane.

Nanostructured, photoactive anatase TiO2 sol prepared under very mild conditions using titanium tetraisopropoxide as the precursor is used to functionalise extruded expanded polystyrene (XPS) sheets by spray-coating resulting in stable and active materials functionalised by TiO2 nanoparticles. Photocatalytic tests of these sheets performed in a batch reactor in gas-solid system under UV irradiation show their successful activity in degrading probe molecules (2-propanol, trimethylamine and ethene). Raman spectra ensure the deposition of TiO2 as crystalline anatase phase on the polymer surface. The presence of TiO2 with respect to polymer surface can be observed in SEM images coupled to EDAX mapping allowing to monitor the surface morphology and the distribution of TiO2 particles. Finally thermoforming of these sheets in industrial standard equipment leads to useful containers for foodstuffs. (C) 2012 Elsevier B. V. All rights reserved.

The presence of (±)α-pinene, (+)β-pinene, (+)3-carene, and R-(+)limonene terpenes in wastewater of a citrus transformation factory was detected and analyzed, in a previous study, by using Solid Phase Micro-extraction (SPME) followed by GC analyses. Purpose of that research was to compare the genotoxic responses of mixtures of terpenes with the genotoxicity of the individual compounds, and the biological effects of actual wastewater. Genotoxicity was evaluated in the Salmonella reversion assay (Ames test) and in V79 cells by Comet assay. Ames tests indicated that the four single terpenes did not induce an increase of revertants frequency. On the contrary, the mixtures of terpenes caused, in the presence of metabolic activation, a highly significant increase of the revertants in TA100 strain in comparison to the control. The Comet assay showed a significant increase in DNA damage in V79 cells treated for 1 h with single or mixed terpenes. Moreover, the actual wastewater was found highly genotoxic in bacterial and mammalian cells. Photocatalytic tests completely photodegraded the pollutants present in aqueous wastewater and the initial high genotoxicity of samples of wastewater collected during the photocatalytic run, was completely lose in 3 h of irradiation.

The aim of this work was to study the biological effects of four monoterpenes, i.e. α-pinene, β-pinene, 3-carene and d -limonene present in the wastewater of a citrus transformation factory. The study was carried out by exposing V79 Chinese hamster cells to single terpene or to the mixture of four terpenes at concentrations corresponding to those in the wastewater evaluated by head space solid phase micro extraction and gas chromatography (HS-SPME-GC) analyses. Treatments with single or combined terpenes similarly affected cell vitality, but only the combined treatments induced the 6-thioguanine resistant mutants. Moreover the photocatalytic degradation of the four terpenes was successfully achieved with the photocatalyst TiO 2 Degussa P25 in both the actual effluent and in synthetic solutions.

The aim of this work was to compare the genotoxic responses of mixtures of terpenes present in wastewaters of a citrus transformation factory with the genotoxicity of the individual compounds. Samplings of wastewater collected before (untreated sample) and past water purification by biological method (treated sample) were analyzed using Solid Phase Micro-extraction (SPME) followed by GC analyses. The chromatograms showed in all effluents the presence of four terpenes: pinene, -pinene, 3-carene, D-limonene. The concentrations of terpenes in the untreated sample were 1–3 orders of magnitude higher than in the treated sample. Genotoxicity was evaluated in the Salmonella reversion assay (Ames test) and in V79 cells by comet assay, by utilizing aqueous solutions the four terpenes at concentrations corresponding at those determined by SPME. In the Ames test, when tested individually, the four terpenes induced no or only a modest increase of genotoxic effects. On the contrary, the mixtures of terpenes present in untreated sample caused an increase highly significant of the revertants in TA100 strain, in presence of metabolic activation, in comparison to the control. The comet assay showed a significant increase in DNA migration in V79 cells after 1 or 6 h treatment with single or mixed terpenes. The possibility to photodegrade terpenes by using polycrystalline TiO2 irradiated with UV light was investigated. Photocatalytic tests carried out on both synthetic and actual aqueous effluents indicated that all terpenes were completely photodegraded, confirming the methodology effectiveness.