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Increasing the photocatalytic efficiency of earth-abundant wide-bandgap semiconductors is of high interest for the development of cheap but effective light-driven chemical conversion processes. In this study, the coupling of ZnO and TiO2 with low contents of the rare-earth Ce species aimed to assess the photo-catalytic performance of the two semiconductors (SC). Structural and optical characterizations were performed to estimate the effect of the different interactions between Zn2+, Ti4+ and Ce4+ ions, and how the photo-responsive behaviour of Ce-Ti and Ce-Zn composites was affected. Therefore, photo-catalytic tests were performed for all Ce-modified SC to assess both their photo-oxidative and photo-reductive properties. Amongst all the tested materials, only Zn-based samples resulted in being suitable for the photo-oxidation of the methylene blue (MB) organic pollutant in a synthetic-dependent fashion.

TiO2 photocatalysts degrade pollutants in both the gas and liquid phase under UV radiation. To widen their application under solar and/or LED light, TiO2 surface decoration with noble metals offers a mean to achieve such a goal. Ag species as a decorating agent improve TiO2-based systems photoactivity and exhibit antibacterial properties under LED light and even in the dark. Ample literature is available on the synthesis of silver nanoparticles (Ag NPs) but few data are available on the interaction of such particles with micrometric samples. Indeed, micrometric samples pose less environmental and health concerns than the nano-sized powders widely adopted. The synthetic routes employed for Ag NPs decoration onto TiO2 clearly influence the photocatalytic activity, in particular referring to both NPs shape and fine structure. Thus, we report the preparation of Ag NPs by an electrochemical method followed by the subsequent decoration onto a micrometric TiO2 (Kronos 1077): different parameters, such as pH and the nature of physical nanoparticle dispersants were taken into account to evaluate their effect on the resulting Ag NPs features. We evaluated the photocatalytic activity towards the photodegradation of NOx under LED light, concluding that the best output was obtained by photocatalysts synthesised at basic pH.

TiO2/WO3 composites are widely in the literature as engineered systems for photocatalytic and (photo)electrochemical applications, since the presence of WO3 can promote both visible light absorption and electron transfer phenomena of TiO2. The preparation of these system, depending on the preparation method, can also affect the surface feature with respect to TiO2, modifying adsorption and performance, as well as the reaction mechanisms. Here, TiO2/WO3 composites were prepared by precipitation of WO3 onto the TiO2 surface and characterized in terms of their structural, morphological, optical and surface properties. Raman and IR spectroscopy as well as a marked shift in the isoelectric point support the preferential surface location of WO3. Samples were photocatalytically tested towards the degradation of ethanol and of tetracycline and the adsorption and degradation behaviour were studied, suggesting, in both cases, significant variations of the reaction paths by the addition of WO3.

The ingredients of Pharmaceuticals and Personal Care Products (PPCPs) persist in water and conventional treatment plants are not able to remove them efficiently. Sonochemical treatment is insufficient to mineralize organics such as ibuprofen into CO2 and H2O. TiO2 degrades ibuprofen (IBP) under UV light; however, it does not reach a high grade of conversion. Here, we investigated the mineralization of ibuprofen to CO2 by TiO2 UV-C photocatalysis. We replaced nano-sized P25 (the standard catalyst) with a micro-sized commercial sample of TiO2 to preclude the use of nanoparticles which are dangerous for human health and because typical filtration systems are expensive and inefficient. We deposited micro-TiO2 on glass Raschig rings to ensure an easy recovery and reuse of the photocatalyst and we studied its performance both with a batch and a continuous reactor. Micro-TiO2 mineralized 100% of IBP in 24 h. TiO2-coated glass Raschig rings degraded 87% of IBP in 6 h of UV-C irradiation in a continuous reactor, with a mineralization of 25%. Electronspray ionization mass spectrometer (ESI-MS, positive mode) analyses identified 13 different byproducts and we hypothised a degradration pathway for IBP degradation.

Currently, photocatalytic reactions under solar illumination have attracted worldwide attention due to the tremendous set of associated environmental problems. Taking sunlight into account, it is indispensable to develop highly effective photocatalysts. Strontium titanate, SrTiO3 (STO), is a cubic perovskite-type semiconductor, an inexpensive material with high thermal stability and corrosion resistance that exhibits a similar energy bandgap to TiO2 and can represent an interesting alternative in photocatalytic applications. Particle size can significantly affect both photocatalytic and photoelectrochemical properties of a photocatalyst, thus altering the photooxidation of organic pollutants in air or water. In this context, this research aims at investigating the photocatalytic features of nano- and micro-sized commercial STO powders towards the photodegradation of diclofenac (DFC), a non-steroidal, anti-inflammatory drug, widely used as analgesic, antiarthritic, and antirheumatic. Both nano- and micro-STO photocatalysts exhibited remarkable photocatalytic efficiency towards DCF, reaching photodegradation efficiency higher than 90% within one hour. Results obtained in simulated drinking water were also compared to those obtained in ultrapure water. Both STOs showed good stability during recycling tests, maintaining high performances after three cycles. Eventually, active species were identified using various scavengers by trapping holes and radicals generated during the photocatalytic degradation process.

The size of TiO2 can significantly affect both its photocatalytic and photo-electrochemical properties, thus altering the photooxidation of organic pollutants in air or water. In this work, we give an account of the photo-electrochemical and photocatalytic features of some nanosized TiO2 commercial powders towards a model reaction, the photooxidation of acetone. Cyclic voltammograms (CV) of TiO2 particulate electrodes under UV illumination experiments were carried out in either saturated O2 or N2 solutions for a direct correlation with the photocatalytic process. In addition, the effect of different reaction conditions on the photocatalytic efficiency under UV light in both aqueous and gaseous phases was also investigated. CV curves with the addition of acetone under UV light showed a negative shift of the photocurrent onset, confirming the efficient transfer of photoproduced reactive oxygen species (ROSs), e.g., hydroxyl radicals or holes to acetone molecules. The photocatalytic experiments showed that the two nano-sized samples exhibit the best photocatalytic performance. The different photoactivity of the larger-sized samples is probably attributed to their morphological differences, affecting both the amount and distribution of free ROSs involved in the photooxidation reaction. Finally, a direct correlation between the photocatalytic measurements in gas phase and the photo-electrochemical measurements in aqueous phase is given, thus evincing the important role of the substrate-surface interaction with similar acetone concentrations. This work has been developed in part in the context of project RTI2018–102061–B–I00 financed by FEDER/Ministerio de Ciencia e Innovación-Agencia Estatal de Investigación.

Photocatalysis is a green technology for tackling water and air contamination. A valid alternative to the most exploited photocatalytic material, TiO2, is bismuth oxyhalides, which feature a wider bandgap energy range and use visible radiation to attain photoexcitation. Moreover, their layered structure favors the separation of photogenerated electron&ndash, hole pairs, with an enhancement in photocatalytic activity. Controlled doping of bismuth oxyhalides with metallic bismuth nanoparticles allows for further boosting of the performance of the material. In the present work, we synthesized Y%Bi-doped BiO(Cl0.875Br0.125) (Y = 0.85, 1, 2, 10) photocatalysts, using cetyltrimethylammonium bromide as the bromide source and varying the chloride source to assess the impact that both length and branching of the hydrocarbon chain might have on the framing and layering of the material. A change in the amount of the reducing agent NaBH4 allowed tuning of the percentage of metallic bismuth. After a thorough characterization (XRPD, SEM, TEM, UV-DRS, XPS), the photocatalytic activity of the catalysts was tested in the degradation of NOx under visible light, reaching a remarkable 53% conversion after 3 h of illumination for the material prepared using cetylpyridinium chloride.

Valorisation of lignocellulosic biomass for chemical production is one of the main challenges of the 21st century. Levulinic acid (LA) has been chosen as the target product due to its potential as an intermediate to produce a wide variety of other chemicals. The attention has been focused on the formulation of an active solid acid catalyst for the hydrolysis of glucose to LA. Therefore, a deep modification of SBA-15 with sulfonic groups was performed using post-synthesis grafting method. In particular, this work focuses on the role of different grafting solvents. Since the traditional solvents such as toluene or hexane, are flammable and toxic, a safer and more environmentally friendly solvent, a mixture of water and NaCl has been investigated. It was found that the nature of the solvent highly affects the morphological and chemical features of the materials. Thus, the best catalytic results were obtained with the catalyst prepared in water and NaCl; indeed 30 % and 16 % of LA yield were obtained from fructose and glucose hydrolysis at 180 °C respectively. Water and NaCl mixture guarantees the best distribution of sulfonic groups over the surface, leading to the most balanced acid catalyst.

TiO2 modification by both non-metal and metal species is a popular strategy to promote the semiconductor visible light absorption and photocatalytic performance. In this work, tin and zinc are compared as metal promoters to enhance the photocatalytic activity of N-doped TiO2 under solar light. The synthesized samples were tested under both UV and simulated solar irradiation toward the photocatalytic degradation of tetracycline, an emerging water pollutant. All copromoted samples (N + Sn and N + Zn) revealed higher efficiency under solar light in the mineralization of the pollutant with respect to both the pristine and N-doped ones. The enhanced photocatalytic efficiency of these samples was traced back to the modifications introduced by the different guest species to the structural (X-ray Powder Diffraction, XRPD), morphological (High-Resolution Transmission Electron Microscopy, HR-TEM and Brunauer-Emmett-Teller analysis, BET), spectroscopic (X-ray Photoelectron Spectroscopy, XPS, Energy Dispersive X-ray Spectroscopy, EDX and Diffuse Reflectance Spectroscopy, DRS) and surface features (ζ-potential). In this regard, the increased surface area, the modifications of the phase composition and the enhanced visible light harvesting seem to play a pivotal role in affecting the photocatalytic performance. Mass spectrometry analyses allowed us to identify several reaction intermediates and propose different degradation mechanisms depending on the type of metal promoter.

We synthesized Ce doped TiO2 (Cex-T) and tested it in the photocatalytic degradation of NOx and ethanol under visible light. Pristine TiO2 (T) and different dopant ratios of Ce-TiO2 (Cex-T; x=0 to 1.0 wt%) were prepared by a water-based sol-gel method followed by spray drying. The successful doping of Ce in the lattice structure of TiO2 was confirmed by several characterizations such as X-ray diffraction (XRD), energy dispersive X-ray (EDX), Fourier transform infrared (FTIR), and Raman spectroscopy. All the prepared catalysts grew as spherical grains with a polycrystalline anatase phase. Ce0.8T revealed the lowest bandgap among all the prepared catalysts (2.8 eV) compared to 3.2 eV for T. The highest degradation of NOx and ethanol was attained by Ce0.8T (26±1% and 23±1%), which was 2.8 and 1.5 times the degradation by T, Furthermore, we proposed the photocatalytic degradation mechanism by the reactive oxidant species (ROS).

In this work, we investigate the ability of mesoporous bioactive glasses (MBGs) modified with cerium ions (Ce 3+ /Ce 4+ ) to act as catalase and superoxide dismutase (SOD) mimetic materials. We have previously reported that the catalytic properties of bioactive Ce-containing glasses based on 45S5 Bioglass ® and synthesized via melting are influenced by: i) composition (presence/absence of P 2 O 5 ); ii) Ce 3+ /Ce 4+ molar ratio. The introduction of cerium species drastically decreased the bioactivity in terms of Hydroxyapatite formation during bioactivity tests in vitro . We thus decided to add cerium to MBGs, a class of glasses with improved bioactivity with respect to classical molten glasses. MBGs exhibit a high surface area and their reactivity is increased with respect to the molten glasses, and they are able to induce the formation of Hydroxyapatite over the surface within shorter times with respect to the 45S5. The catalase and SOD mimetic activity tests revealed that the Ce-MGB are able to act as mimetic materials for the two enzymes. Both Infrared Spectroscopy and X-ray diffraction analysis have confirmed the presence of Hydroxyapatite over both 80SiO 2 –15CaO–5P 2 O 5 , and 80SiO 2 –20CaO samples modified by 5.3% mol of CeO 2 ; simultaneously the glasses maintain a good catalase activity. Moreover, the 80SiO 2 –15CaO–5P 2 O 5 potential bioactive glasses showed SOD mimetic activity. These results highlight that it is possible to obtain a glass with both antioxidant and bioactivity properties.

TiO

The photocatalytic degradation of NOx in the gas phase was investigated comparing several commercial TiO2 sold as pigmentary-powders and characterized by crystallite sizes ranging from nano to micrometer dimensions. In particular the photocatalytic activity of the micro-sized sample was evaluated in comparison with the well-known activity of the nano-sized samples, being these last photocatalysts potentially dangerous due to the risk towards the human safety. The studied samples were precisely chosen among different commercially available products on the basis of the following features: pure anatase, uncoated surface, undoped material, not sold as photocatalytic materials. All samples reveal good photoactivity in the photodegradation of NOx in gas phase with an evident superiority of the nano-sized sample. However, the gap of activity between nano and micro-sized samples tends to be canceled when the starting NO2 concentration was reduced and fixed from 1000 to 200 ppb, a precise amount that is the first alert threshold for NO2 in air (World Health Organization). A proper kinetic model, based on the Langmuir–Hinshelwood mechanism and on the hypothesis of irreversible adsorption of the products on the catalysts surface, has been developed and discussed.

Pharmaceutical compounds and their metabolites raise worrying questions because of their continuous release and lack of efficient removal by conventional wastewater treatments; therefore, they are being detected in groundwater, surface water and drinking water in increasing concentrations. Paracetamol and aspirin are two of the most commonly used drugs employed as fever reducer, analgesic and anti-inflammatory. They and their metabolites are very often found in river water, so their degradation is necessary in order to render water suitable for human consumption. The present work is focused on the comparison of the photocatalytic performance of industrial active grés porcelain tiles covered with a commercial micro-sized TiO

Aim of this work is the synthesis of titanium-based photocatalysts co-doped with both C and N, exhibiting improved photocatalytic activity under visible light irradiation. The preparation of the catalysts consists of a two step process: during the first one, the synthesis of the catalyst doped with nitrogen has been carried out, whereas in the second step carbon has been introduced in different amounts. The photocatalytic activity has been evaluated in the gas phase reaction of NOx abatement under visible light irradiation. The characterization has been carried out by N2 physisorption, TPO (temperature programmed oxidation), DRS (diffuse reflectance spectroscopy) and XPS (X-ray Photoelectron Spectroscopy) in order to investigate both structural and physico-chemical features of the samples and their correlation with the catalytic activity. An effective promotion effect of the dopants has been observed; in particular, the synergic co-presence of both N and C produced a significant narrowing of the TiO2 band gap with the consequent extension of the photocatalytic activity towards the visible part of the light spectrum.

Volatile organic compounds (VOCs) are prevalent components of indoor air pollution. The photocatalytic degradation could be an interesting method to degrade them. This paper reports the photoactivity study of two classical nano-sized and two micro-sized commercial TiO 2 powdered samples. Photocatalytic tests have been performed following the degradation of acetone, acetaldehyde and toluene in the gas phase under UV light. An accurate study of the intermediate oxidation products was performed. XPS and FTIR analyses allowed to highlight the relationship between TiO 2 surface properties and reactivity toward VOCs explaining the different behavior of the photocatalyst in case of hydrophilic and hydrophobic pollutants.

Gold-based catalysts over different supports were investigated in the oxidative esterification of furfural by employing an efficient and sustainable process. The catalytic performances follow the trend: Zirconia–Au > Ceria–Au ≫ Titania–Au. Zirconia came out to be the best support option to promote activity, selectivity and also stability. The chemical and morphological properties observed for zirconia-supported sample seem to fulfill a good compromise between high gold dispersion and the presence of suitable acid–base properties, for good selectivity. Moreover, stability and recycling of the catalysts were also investigated.

WO3/ZrO2 systems were prepared by sol–gel technique using different procedures for the solvent extraction: evaporation in vacuum at room temperature (xerogel) and extraction in supercritical conditions (aerogel). Two reactions of industrial interest were investigated under mild conditions: (i) acylation of veratrole with acetic anhydride; (ii) acylation of anisole with benzoic anhydride. Several techniques were employed in order to study the influence of the synthetic parameters on texture and catalytic activity: N2 physisorption, Fourier transformed-infrared spectroscopy, X-ray photoelectron spectroscopy, temperature programmed reduction and temperature programmed oxidation analyses. The solvent extraction strongly influences metal reducibility, surface area, pores organisation, W/Zr surface density and metallic interactions. The aerogel sample shows the best catalytic results for both conversion and yield. The supercritical extraction plays a central role especially in the recycling: by proper air activation, the aerogel sample attains the complete restoration of the catalytic activity even after three runs.

Micro-sized TiO

A CoFe2O4 inverse spinel calcined at two different temperatures (450 and 750 °C), in order to modulate the growth of the crystallites, has been employed in methanol anaerobic oxidation. A correlation between physicochemical properties and catalytic performances of the material has been pursued. The study of both surface and bulk properties has been carried out by means of different experimental techniques, among which are X-ray diffraction (XRD), transmission electron microscopy (TEM), and in situ FTIR spectroscopy. The FTIR study of both bulk and surface spectral features reveals that the calcination step is responsible for the different type of exposed surface sites and as a consequence for the different catalytic behavior. As the use of the spinel as the catalyst for methanol transformation into H2 necessarily implies a regeneration step with steam, in order to recover the oxidative capacity of the solid, both surface and bulk features of the reoxidized solids have been also studied. All results reveal that the two samples, originally morphologically quite different from one another, become very similar after just one redox cycle. Still, it has been also demonstrated that both used materials irreversibly modify their surface properties after the reduction/oxidation process.

TiO2-based photocatalysis under visible light is an attractive way to abate air pollutants. Moreover, developing photocatalytic materials on a large-scale requires safe and low-cost precursors. Both high-performance TiO2 nanopowders and visible-light active noble metals do not match these requirements. Here, we report the design of novel Mn-decorated micrometric TiO2 particles. Pigmentary TiO2 replaced unsafe nano-TiO2 and firmly supported MnOx particles. Mn replaced noble metals such as Au or Ag, opening the way for the development of lower cost catalysts. Varying Mn loading or pH during the impregnation affected the final activity, thus giving important information to optimize the synthesis. Photocatalytic activity screening occurred on the gas-phase degradation of ethanol as a reference molecule, both under ultraviolet (UV) (6 h) and Light Emitting Diode (LED) (24 h) irradiation. Mn-doped TiO2 reached a maximum ethanol degradation of 35% under visible light after 24 h for the sample containing 20% of Mn. Also, we found that an acidic pH increased both ethanol degradation and mineralization to CO2, while an alkaline pH drastically slowed down the reaction. A strict correlation between photocatalytic results and physico-chemical characterizations of the synthesized powders were drawn.

Fe- and Mn-promoted ZrO2–SO4 (ZS) powders were prepared both by a single step sol–gel reaction and by impregnation of the zirconia hydrous precursor. The samples were calcined at 890 K and characterized for the structural (XRD) and morphological features (BET method). Surface functionalities were investigated by XPS, 1H MAS NMR and FTIR analyses. The liquid medium catalytic activity was tested with respect to both the esterification of benzoic acid to methylbenzoate and the benzylation of toluene. The acidity features appeared not to be significantly different among the various samples while all surface characterizations showed a lower affinity to retain water by the metal-promoted samples with respect to ZS, the more so in the case of iron-containing samples. The presence of Mn reduced the surface area and depressed the catalytic activity. Iron-doped catalysts appeared, instead, to be more efficient than ZS especially for the benzylation of toluene.

Highly toxic o-toluidine pollutant was photo-degraded in water by using ZnO nanoparticles. The tested powders were both commercial and laboratory-made, the latter obtained by means of two innovative synthetic procedures. The disappearance and the relative mineralization of the molecule were followed by HPLC/UV and TOC determinations, respectively. Intermediate products were identified by coupling LC/MS of the eluate after 3 h of reaction and ATR-FTIR analyses of the used ZnO powders at the end of photocatalytic tests. Selected degradation paths, characterized by different kinetic degradation rates, can be suggested as a function of the different surface texture, the effective photocatalytic active area and the e−/h+ recombination processes of the ZnO particles.

The aerobic oxidation of trans-1,2-cyclohexanediol in the synthesis of adipic acid was studied. Two classes of catalysts are compared, 1) alumina-supported Ru(OH)3, and 2) Keggin type P/Mo/V polyoxometalates. These two classes are representative examples because they are active in alcohol oxidation under quite different reaction conditions. In the former case, basic conditions are needed in order to activate the substrate, whereas with polyoxometalates, acidic conditions are used. Their catalytic behavior showed remarkable differences; in basic conditions, the reaction network was very complex, and several side reactions led to a number of by-products, with a low selectivity to adipic acid in the end. The supported Ru(OH)3 catalyst was very efficient in 1,2-cyclohexanediol oxidative dehydrogenation to 1,2-cyclohexanedione, but several undesired reactions occurred starting from this key intermediate under basic conditions: rearrangement into 6-hydroxycaprolactone and 1-hydroxycyclopentanecarboxylic acid, and formation of the product of aldol condensation. The former compound was also an intermediate for adipic acid formation, but this reaction gave only a minor contribution to the reactant conversion. Polyoxometalates were extremely selective in 1,2-cyclohexanediol conversion into adipic acid, but under acidic conditions the product reacted with the unconverted reactant to yield the corresponding ester.

TiO 2 –montmorillonite composite (TiO 2 –M) was prepared by impregnation with TiCl 4 followed by calcination at 350 °C. The synthesized material was characterized by FTIR, TG–DTA, BET, XRD and SEM–EDX. The results show that TiO 2 was efficiently formed in Na–montmorillonite (Na–M) framework, and only a crystalline, pure anatase phase was produced. Photoactivity tests were carried out under UV-A irradiation using five selected organic dyes. The results indicate that the activity of TiO 2 –M is more important for cationic dyes, where the removal rates are in the order: crystal violet (97.1%) > methylene blue (93.20%) > rhodamine B (79.8%) > methyl orange (36.1%) > Congo red (22.6%). The results of the TiO 2 –M activity were compared with that of the commercial P25. The comparison demonstrates that the synthesized TiO 2 –M exhibits a higher adsorptive behavior and can be used as low-cost alternative to the commercial TiO 2 for wastewater treatment, showing also an extreme easiness to completely recover the composite catalyst at the end of the test.

Although the TiO2 is one of the most promising materials for its photocatalytic potential related to the pollution abatement, it strongly suffers from the low photocatalytic activity if it is used under visible light and not under UV light. Among the various possible modifications, the surface decoration with metal or metal oxides NPs can be a good strategy to increase the potential of TiO2 in the visible range. In this paper, a sonochemical method that exploits the use of high-energy ultrasounds is suggested to obtain this surface decoration. The support is a commercial and micrometric TiO2, cheaper and easier to handling than the nanometric P25. Samples were tested on the photodegradation of toluene and acetone in a gas phase system, using both the UV and LED lamp.

Ga 2 O 3 -promotion of ZrO 2 /SO 4 (SZ) systems has been shown to influence the catalytic activity of n -butane isomerization. This contribution reports a study on the influence of Ga 2 O 3 addition and of calcination temperature on ZrO 2 structure, morphology and activity. Small additions of Ga 2 O 3 (1–5 mol%) bring about an increase of specific surface area (SSA). By N 2 physisorption, X-ray diffraction, Raman spectroscopy and TEM microscopy, the increase of an amorphous phase and the decrease of SSA were observed when the Ga 2 O 3 content raised above 5 mol%. The catalytic activity went through a maximum with Ga loading of 3–5 mol%. In all cases, the typical spectral features of surface sulfates were observed, but they became more and more confused as the Ga 2 O 3 content increased. DTG/DSC measurements showed that Ga 2 O 3 addition tends to slow down both the formation of ZrO 2 crystallites and the thermal elimination of surface sulfates. After calcination at temperatures as high as 720 °C, the amount of amorphous phase is drastically reduced and an appreciable fraction of surface sulfates is lost. In particular, 15 mol% Ga 2 O 3 -doped SZ sample, which is amorphous and inactive in n -butane isomerization after a standard calcination at 650 °C, exhibits tetragonal crystalline features and a dramatic improvement of catalytic activity after a thermal treatment at 720 °C. TPR-MS analyses showed that Ga 2 O 3 -promoted SZ catalysts possess enhanced redox properties, with respect to plain SZ systems, and this can probably account for the higher catalytic activity.

Sulphated zirconia (SZ) was synthesized under different precipitation and ageing conditions. Catalysts were characterized by nitrogen adsorption–desorption, thermal analysis, FTIR and Raman spectroscopy. The catalytic performance of these SZ systems in both gas and liquid-phase reactions has been investigated. The effect of precipitation and ageing conditions has been studied and a correlation with catalytic activity has been tried.

The RT adsorption of CO2 was studied in order to compare the surface acid-base properties of yttria-stabilized tetragonal ZrO2, either plain or variously sulfated. The nature of the species formed upon CO2 adsorption, as well as their stability upon outgassing, was monitored by IR spectroscopy, whereas the population of the sites and their energy distribution was studied by microcalorimetry. The effect of sulfation on the basicity of cus Zr4+/O2- pairs and on the Lewis acidic strength of cus Zr4+ cations, as well as the influence of calcination on the amount and nature of surface sulfates were studied and correlated with the catalytic activity of SZ systems.

In this work the performance of CaO-doped Ni/ZrO2 catalysts in ethanol steam reforming was studied. The addition of CaO did not affect the morphology or the crystalline structure of the support. On the contrary, Ni reducibility markedly increased. Moreover, the Lewis acidity of zirconia gradually decreased as the CaO content increased, thus inhibiting coke deposition and improving the carbon balance. The addition of a basic oxide helps to prevent some of the side reactions responsible for coke formation and deposition, that can gradually deactivate the catalyst. (C) 2013 Elsevier B.V. All rights reserved.

The room temperature adsorption of CO2 on pure and sulphated tetragonal ZrO2 (t-ZrO2) was studied, in order to assess how and to what extent the acid–base properties of ZrO2 are modified by the presence of surface sulphate groups. The formation of different species, as well as their stability upon outgassing, was monitored by IR spectroscopy (2000–1000 and 2400–2300 cm−1 regions), whereas the population and the distribution of sites of different kind was quantitatively and energetically characterised by adsorption microcalorimetry. The formation of carbonate-like species was found to be a highly energetic (qads>100 kJ/mol) and irreversible process, occurring only on the (at least partially) dehydrated surface of pure t-ZrO2. Bicarbonate-like (hydrogen-carbonate) species (either of stable type) were found to form on both pure and sulphated t-ZrO2 specimens, and to be accompanied by a heat of adsorption variable in the 100–40 kJ/mol range. The presence at the surface of sulphate groups causes the basicity of the t-ZrO2 matrix to be dramatically depressed, the most basic OH− and/or coordinatively unsaturated (CUS) O2− ions being preferentially consumed by the sulphation process. Linear coordinated CO2 complexes were also found to form on CUS Zr4+ cations, the acidic strength of which increases with the extent of surface dehydration and as a consequence of the presence of charge-withdrawing surface sulphate groups.

Cubic sulfated zirconia (c-SZ) was prepared by sulfating phase-stabilised c-ZrO2, and its properties are compared with those of tetragonal (t-SZ) and monoclinic (m-SZ) systems. ZrO2 crystalline phases have been identified by XRD and, far more efficiently, by Raman spectroscopy. c-SZ exhibits better catalytic activity (n-butane isomerization at 423 K) than t-SZ, whereas m-SZ is virtually inactive. The better activity of c-SZ is not ascribable to changes of surface functionalities, but probably derives from a better stabilization of the high symmetry crystalline form (i.e., from a more favourable distribution of surface sulfates among regular and defective crystal terminations).

When high-area oxidic systems carry surface anionic species (in the present case: stable sulfate groups at the surface of sulfated zirconia catalysts), pyridine adsorption leads to an overestimated and thus partly artefact evaluation of the surface Lewis acidity. IR spectroscopic evidence is presented for the existence of a ligand competition at surface cationic centres (Lewis acid sites) between strong Lewis bases (pyridine) and surface sulfates. In the case of weak Lewis bases, like CO, there is no competition. The use of a “model” sulfated zirconia system, obtained by sulfation of an yttria-stabilized tetragonal zirconia preparation, turned out to be vital for obtaining the mentioned evidence, as this preparation allowed to compare the surface Lewis acidity in an homogeneous series of non-sulfated, sulfated, and sulfated-and-calcined systems of virtually unchanged crystal phase, surface area and crystal morphology. Also the conventional sulfated zirconia catalysts, prepared from an amorphous hydrate precursor, present the same type of surface ligand competition and the partly artefact evaluation of surface Lewis acidity, but in that case a piece of information is missing in that physical and chemical properties of the non-sulfated amorphous precursor cannot be compared with those of the crystalline sulfated systems.

IR spectra of surface species and of CO adsorption at ∼77 and ∼300 K on pure ZrO2, sulfated ZrO2, sulfated/calcined ZrO2 have been obtained and related to the catalytic activity of these systems in the isomerization of n-butane. Spectral data indicated that: (i) the catalytic activity, when present, requires the presence of both Bronsted and Lewis surface acidity; (ii) a catalyst calcination step is necessary for the elimination of sulfates from crystal defects, on which strong Lewis acid sites must form; (iii) strong Lewis acid sites actually involved in the catalytic process represent a small yet strongest fraction of all Lewis sites formed on the catalyst upon thermal activation.

A Fourier transform infrared (FTIR), UV−vis, and high-resolution transmission electron microscopy (HRTEM) study of fresh and used Au/ZrO2 catalyst is reported. FTIR data show that on a fresh sample CO is adsorbed on regular gold metallic sites, while on the used sample the adsorption sites are bidimensional gold clusters made positive by interaction with the support. NIR−UV−vis reflectance spectra show that the gold plasmonic peak appears broader and the ZrO2 absorption edge weaker on the used sample with respect to the fresh one. HRTEM indicates the disappearance of the gold metallic particles in the used catalysts. Moreover, a strong reduction in the CO oxidation activity has been evidenced on the used sample and ascribed to the positivization of gold and/or to the decrease of the number of highly uncoordinated gold sites, consistently with the spreading of gold at the support surface.

In situ FTIR spectroscopy has been used to study the adsorption at ∼77 K of CO on (i) tetragonal zirconia (t-ZrO2), (ii) non-calcined sulfated tetragonal zirconia (t-SZ) and (iii) calcined sulfated tetragonal zirconia ([t-SZ]C). CO adsorption at low temperature turned out to be a suitable probe to test the surface charge-withdrawing properties of the various zirconia-based systems. On t-ZrO2 it has been possible to distinguish the H-bonding adsorption of CO on at least two families of acidic surface OH groups and the coordinative adsorption of CO on surface Lewis acidic sites (i.e. coordinatively unsaturated Zr4+ surface centres) located either in regular patches of low-index crystal planes (the `top' termination of ZrO2 crystallites) or in defective terminations of the particles (the `side' termination of ZrO2 crystallites). On t-SZ, virtually only CO uptake by H-bonding on some surface OH groups is observed, as virtually all of the non-hydroxylated parts of the surface are occupied and maintained coordinatively saturated by sulfate groups. On [t-SZ]C, the calcination process selectively eliminates the sulfates that were initially located in the defective crystal terminations. As a consequence CO uptake reveals, besides two well resolved families of OH groups yielding adsorption by H-bonding, two well resolved families of Lewis acid sites located in defective crystal terminations (strong Lewis sites), whereas no CO uptake occurs in the regular terminations of the crystallites. The latter crystal positions remain occupied by a family of sulfates, that turn out to be responsible for the catalytic activity of [t-SZ]C systems.

The catalytic activity in the isomerization of butane of a variety of zirconia sulfate catalysts, both unpromoted (AZS samples) and promoted with Pt (PZS samples), prepared by an aerogel technique, is reported. Catalysts have either different sulfate contents (AZS samples) or different Pt content and constant sulfate content (PZS samples). Catalysts are studied in a continuous flow system at 150 and 250°C, both in the absence and in the presence of hydrogen in the feed. AZS samples have identical specific activity at 150°C, while differences are observed at 250°C both in the absence and in the presence of H 2 . PZS samples are more active and stable, particularly when activated in air only. No effect of Pt content on the catalytic activity is observed in the range explored (0.65–4.96%), while a negative effect of hydrogen can be evidenced under suitable conditions. An FTIR analysis performed on both AZS and PZS samples using a procedure that mimick the catalysis conditions suggest that contamination of the active sites on stream is mainly due to water and, in the absence of H 2 in the feed, to coke or oligomers deposition. A reaction mechanism is proposed involving an intermediate intermolecular butane dimerization where Zr 4+ Lewis acid centers promote the initial C4 carbenium ion formation, followed by addition to in situ formed butene. The roles of Pt in the catalysis are also discussed.

The population of coordinatively unsaturated (cus) Zr4+ ions acting as strong Lewis acid sites on superacid sulfated zirconia catalysts, as well as the relevant heats of adsorption, were measured by means of CO adsorption at 303 K. The presence of charge-withdrawing SO4 groups slightly enhances the electron-accepting ability of the residual free surface cations, not involved in sulfate/metal complexes. H2O adsorbed at 303 K by a stepwise procedure progressively eliminates the Lewis acidic sites, through a mechanism that suggests a competition in strongly binding H2O between cus Zr4+ cations and SO4 groups. Quantitative and energetic data are reported and correlated to IR spectroscopic and catalytic data previously reported on the same catalysts. A model for the catalytic active site is proposed, based on the assumption that a strict cooperation between Lewis and Bronsted acidic sites is likely to exist.

The surface acidity (of both Lewis and Bronsted type) of an anion-free t-ZrO 2 , stabilized in the tetragonal form by forming a solid solution with ca. 3 mol% Y 2 O 3 , of the corresponding sulfated t-ZrO 2 (SZ) system, and of another SZ t-ZrO 2 system prepared through a conventional method have been compared; the two SZ systems turned out to be essentially equivalent. By FTIR and microcalorimetry it was observed that the presence of sulfate modifies to a very limited extent both the concentration an strength of the types of strong (aprotic) Lewis sites that can be revealed by CO adsorption at 300 K. In absolute terms, the acidity of these Lewis sites turns out to be definitely lower than that of typical acidic oxides (e.g., catalytic aluminas). IR spectroscopic data indicate that surface sulfates induce in SZ systems the presence of (protonic) Bronsted acidity, otherwise absent in (anion-free) t-ZrO 2 . On SZ, Bronsted-acid centres are present over the whole vacuum-activation temperature range explored (300–823 K), though in decreasing amounts with increasing temperature. The acid strength of Bronsted sites is confirmed to be definitely lower than that of typical protonic oxide systems (such as, for instance, H-exchanged zeolites). As the Lewis-acid sites present on SZ systems are not particularly strong, and the Bronsted-acid sites present on SZ systems in catalytic conditions are not particularly strong (nor very abundant), it is concluded that the unique catalytic properties of SZ systems, sometimes termed superacid catalysts, must have another origin, possibly connected with the simultaneous presence at the surface of SZ of acid sites of both types.

Through a one-step sol-gel synthetic method, several sulfated zirconia systems with different sulfate content and several Pt-promoted sulfated zirconia systems with a fixed amount of sulfate and different amounts of Pt were prepared. S and Pt in the resulting catalysts were determined by analytical methods. Crystallographic and morphological features of the ZrO2support and, where present, of the supported Pt were examined by XRD and TEM. The adsorptive capacity of Pt-promoted systems toward H2and O2was determined with a pulse-flow system, and toward CO both with a pulse-flow system and by FTIR spectroscopy. FTIR was also used to characterize the sulfate species present at the surface of the various systems, and to evaluate the resistance of surface sulfates toward vacuum thermal treatments and toward reductive treatments at various temperatures; the latter property was also determined by TPR–MS. The preparation method leads to catalysts that are either pure tetragonal or mainly monoclinic, depending on the amount of sulfuric acid. Reductive treatments deactivate (shield) the exposed Pt, whereas oxidative treatments reactivate it; the presence of Pt, which is known to improve the performance and the stability of sulfated ZrO2systems, renders surface sulfates much easier to eliminate either by thermal treatmentin vacuoor by reduction in H2.

The catalytic properties of Fe,Mn-promoted sulfated zirconia catalysts have been tested as a function of: (i) the temperature of the preliminary calcination step; (ii) the conditions of the catalyst activation step; (iii) the temperature of the catalytic reaction. It was observed that the promotion effect is mainly ascribable to the Fe component, and requires: (i) a preliminary calcination at Tcalc>850 K, most likely to liberate from sulfates as much as possible of the surface Fe component; (ii) an activation cycle (at Tact≈ 700 K) in strictly oxidizing conditions, in order to have as much as possible of the surface FeIII component in a reducible form; (iii) reaction temperatures close to ambient temperature, in order to prevent the predominance of poisoning reactions and to avoid an extensive reduction of the Fe component. When the Fe component becomes reduced, the catalytic promotion effect is lost, and the reduced Fen+ component (n>3) can be easily revealed by the ambient temperature adsorption of CO, which yields a typical IR band centered at ~2170 cm-1.

Different samples of sulphated zirconia and mixed zirconia/titania ( SO 4 2 - / ZrO 2 and SO 4 2 - / 80 % ZrO 2 – 20 % TiO 2 ) were prepared with traditional- and ultrasound (US)-assisted sol–gel synthesis and tested in the free fatty acids esterification. The catalysts were characterized through acid sites quantification by ion exchange, specific surface area and porosity measurements (N2 adsorption at 77 K), XRD, XPS and FT-IR spectroscopy. SEM–EDX and TEM analyses were also used to investigate the morphology of the samples. The results of this study demonstrate the possibility of increasing the acidity and the surface area of sulphated zirconia through the addition of TiO2 and tune the same properties with the continuous or pulsed US. It is also demonstrated that it is necessary to combine specific values of both acidity and surface area and which type of active sites are essential to obtain better catalytic performances in the free fatty acids esterification.

A new innovative methodology for the single-stage preparation of ZrO2-SO4 and Pt/ZrO2-SO4 catalysts is reported, based on the sol-gel technique. Catalysts are characterized by analysis, XRPD, BET and IR methods and are tested in the isomerization of butane.

A series of titanium oxides was prepared by using a surfactant-template method (STM) and used as a carrier for the sustained release of ibuprofen, which was chosen as a model drug. This STM provides an efficient route to TiO(2) matrices with both high surface area (when compared with those that were obtained by using traditional synthetic approaches) and well-defined mesoporous textures. Some parameters of the synthetic procedure were varied: pH value, surfactant, and thermal treatment. The physicochemical nature of the surface carriers were investigated by means of N(2) -physisorption measurements and FTIR spectroscopy. The effect of the amount of drug on the release kinetics was also investigated. The drug delivery was evaluated in vitro in four different physiological solutions (that simulated the gastrointestinal tract) to analyze the behavior of the TiO(2) -based systems if they were to be formulated as oral DDSs. Our optimized approach is a good alternative to the classical methods that are used to prepare efficient TiO(2) -based drug-delivery systems.

The enzyme soybean peroxidase (SBP) is able to catalyze the oxidation of a large number of substrates and is characterized by high resistance to both chemical and thermal denaturation. In this contribution SBP was covalently immobilized on aminopropyl glass beads (APG) in order to obtain a solid biocatalyst, useful either in degradation of pollutants or in specific oxidative reactions. Several samples of immobilized SBP were first synthesized and then characterized by means of some experimental techniques (FT-IR, ESR, and UV–visible spectroscopies, gas-volumetric adsorption of nitrogen at 77 K, SEM). Moreover, different kinetic measurements were carried out to determine activity and stability properties of these biocatalysts. Our data indicate that (i) the SBP catalytic site was partially modified during the immobilization process, but the enzyme retained about 35% of its specific activity after immobilization, and (ii) the biocatalyst exhibits a significant improvement of SBP stability over time, preserving up to 50% of its initial activity after 70 days of storage and 85% when used in ten consecutive reaction cycles.

XRD, HRTEM, and FTIR spectroscopy have been used to characterize the structure, morphology, and surface acidic activity of a family of sulfate-doped ZrO2 systems, prepared by (low loading) sulfation with H2SO4 of ZrO2 from Zr isopropoxide. Crystallinity and morphological features of the sulfated ZrO2 systems are found to vary with preparative and activation conditions. Type and relative concentration of surface acidic sites (both Bronsted and Lewis centres) turn out to depend primarily on type and relative concentration of surface sulfates, which in turn depend on several preparative parameters. The role played by three of them is examined: the temperature of calcination of the nonsulfated ZrO2 precursor, the overall surface concentration of sulfates, and the temperature of vacuum thermal activation of the sulfated ZrO2 system. The ambient temperature adsorption of pyridine and of carbon monoxide, investigated by in situ FTIR spectroscopy, yield complementary information on the nature and heterogeneity of surface acidic centres.

Characterization by high-resolution transmission electron microscopy of differently pretreated Cu/TiO[sub 2] samples and IR and mass spectroscopic studies of NO-CO interaction on them from room temperature to 473 K are presented. All samples are characterized by Cu particles well dispersed on TiO[sub 2] surface. The adsorption of CO produces an absorption in the 2112-2130 cm[sup [minus]1] frequency range; the intensity and position of the band strongly depends on the sample pretreatment, and it is strongly affected by NO interaction. NO dosing on a sample reduced at low temperature (LTR) precovered with CO leads to the formation of some CO[sub 2] but the reaction is not complete after heating at 473 K; on a sample reduced at high temperature (HTR) large amounts of N[sub 2]O and Co[sub 2] are detected already after short contact times at room temperature. By heating at 473 K an almost complete conversion to CO[sub 2] and N[sub 2] is observed. On both LTR and HTR samples neither NO nor isocyanate-adsorbed species are detected. Reaction products are observed if the sample HTR is contacted, after outgassing of a previous interaction mixture without desorption of the oxygen atoms produced in the NO dissociation, with a 1:1 NO-CO mixturemore » or with CO and then with NO. If NO is preadsorbed prior to CO dosing in a second run of the reaction, almost no N[sub 2]O and CO[sub 2] are observed. The experimental data indicate that HTR Cu/TiO[sub 2] is significantly more active than LTR Cu/TiO[sub 2], the activity being related to an easy dissociation of the NO molecules, determined by an electron transfer from reduced titania to antibonding orbitals of the NO. Free reduced copper sites are needed for CO activation, the reaction being to some extent inhibited by NO oxidation of the copper. 20 refs., 9 figs., 1 tab.« less

Several sulfate-doped ZrO2 catalysts (s.d.-ZrO2) have been prepared by sulfating, with either sulfuric acid or ammonium sulfate, samples of monoclinic ZrO2, Y2O3-stabilized tetragonal ZrO2, and amorphous Zr hydroxide, and by calcining the sulfated precursors at T ≥ 673 K. We then examined (by TEM, XRD, FTIR, and catalytic tests) the effect of sulfation on ZrO2 crystal phase and morphology, the effect of ZrO2 crystal phase on the spectroscopic features of the surface sulfate groups, and the catalytic behaviour of the three families of s.d.-ZrO2 systems in the isomerization of n-butane. It could be concluded that the sulfated monoclinic ZrO2 phase is catalytically not very active (if at all), the nonstabilized tetragonal ZrO2 phase is unstable to the sulfation process, and the sulfated tetragonal ZrO2 phase is catalytically active, no matter what the preparative route has been, provided that the sulfated system is calcined at T ≥ 823 K. The latter condition is discussed in terms of the structural and spectroscopic features of the surface sulfate layer.