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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.

The reaction of small-grain Bioglass® 45S5 in artificial saliva (AS), to produce a layer of hydroxy-apatite (HA) and/or hydroxy-carbonate apatite (HCA), has been studied and compared to the results obtained in a simple buffered solution (TRIS). Some potentially bioactive glasses based on the composition of Bioglass® and containing CaF2 (HCaCaF2 5% and HNaCaF2 5%) have also been studied, in order to analyze the effects/changes produced when a F-containing glass surface is contacted with AS. The insertion of fluorine has been proposed to improve bioactive glass bone-bonding ability, and to parallel fluorine-containing glass-ceramics currently used in dentistry. ICP-OES analysis of the solution, and FTIR spectroscopy of the solid samples provided compositional information on the stages of reaction. These data were integrated with XRD and the textural and morphological data, obtained by specific surface areas determination and TEM-EDS measurements. In the case of Bioglass® 45S5, a comparison at corresponding reaction times indicates that the precipitation of an amorphous Ca-phosphate phase is faster in AS, but the crystallization of HA/HCA is delayed in AS with respect to the TRIS solution. For fluoride-containing glasses, the sample HCaCaF2 5%, in which CaF2 replaces part of CaO, possesses the fastest rate for HA/HCA crystallization (1 week) in AS. Some lines of interpretation for these results are proposed.

The combined use of adsorption microcalorimetry/gas-volumetry and in situ FTIR spectroscopy was employed to investigate qualitative and quantitative/energetic aspects of the ambient (beam-) temperature adsorption of acetone on silica-supported Al, Zr, and Ca oxides. All oxidic systems examined possess strong Lewis acidity, though of different strength (Al > Zr > Ca), whereas only the first two mixed oxides present Bronsted acidity of comparable strength. Acetone uptake yields different types of molecular adsorption: two types of H-bonding interaction with surface silanols, as typical of pure silica systems; coordinative interaction with Lewis acidic sites, part of which is not vacuum reversible at ambient temperature in the case of Al- and Zr-doped systems; strong H-bonding interaction with Bronsted acidic centers (when available), a large fraction of which is not vacuum reversible at ambient temperature. In addition, and only on the Ca-doped system, acetone undergoes the aldol condensation reaction yield...

Bioactive glasses containing gold nanoparticles (AuNPs) have been synthesized via the sol-gel route using HAuCl(4) x 3 H(2)O as gold precursor. The formation process of AuNPs was studied as a function of the thermal treatment, which induces nucleation of Au particles and influences their nature, optical properties, shape, size, and distribution. The physicochemical characterization indicates that the sample treated at 600 degrees C presents the best characteristics to be used as a bioactive material, namely high surface area, high amount of AuNPs located at the glass surface, presence of micropores, and abundant surface OH groups. In the case of samples either aged at 60 degrees C or calcined at 150 degrees C, AuNPs just begin their formation, and at this stage the gel is not completely polymerized and dried yet. A thermal treatment at higher temperatures (900 degrees C) causes the aggregation of AuNPs, forming "AuMPs" (i.e., Au microparticles) in a densified glass-ceramic material with low surface area, absence of pores, and low number of surface OH groups. These features induce in the glass-ceramic materials treated at high-temperatures a lower bioactivity (evidenced by SBF reaction), as compared with that exhibited by the glass samples treated at 600 degrees C.

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.

This paper reports a physico-chemical study devoted to reactivity towards hydroxo-carbonate apatite (HCA) formation of bioactive glass 45S5 (H glass; commercially known as Bioglass) and of two preparations of zinc-doped 45S5-derived systems (HZ5, HZ20), immersed in Tris(hydroxymethyl)aminomethane (Tris) and Dulbecco's modified Eagle's medium (DMEM) buffer solutions. The activity/toxicity of the glasses was also tested using endothelial cells (EC). Zn caused a drastic reduction in the overall leaching activity of glasses and, at high Zn concentration (HZ20), the formation of HCA on the glass surface was thoroughly inhibited. The presence of Zn also decreased the increment of pH after glass immersion in both Tris and DMEM solution. EC are known to be very sensitive to pH changes and, for this reason, the rapid increase in pH brought about by H glass dissolution is likely to affect cell adhesion and spreading, whereas the high zinc release from HZ20 causes a drastic reduction in cell proliferation after a long contact time (approximately 1 week). This study shows that only HZ5 glass containing 5 wt.% Zn presents at the same time: reduced solubility, bioactivity (monitored by HCA formation) and conditions allowing EC growth over a 6-day period.

This work, by means of Raman spectroscopy, studies the vibrational modifications of a silica-based sol-gel bioactive glass (77S) in direct contact with a simple TRIS-buffered solution. The novelty of this contribution with respect to similar previous works consists in the adoption of an in situ setup, designed to avoid all kinds of external contamination. The time-dependent formation of the characteristic vibrational features of surface hydroxy-carbonate apatite (HCA) is evidenced, and followed as a function of contact time. Copyright © 2007 John Wiley & Sons, Ltd.

Morphological and structural variations of particles of Bioglass with two different grain sizes reacted in Tris-buffered solution were analyzed by means of N(2) adsorption/desorption at 77 K and HR-TEM/EDS. A remarkable increase in specific surface area (ssa) was observed after the first hour of dissolution. A plateau value corresponding to an increase of at least 2 orders of magnitude was reached after 2 days of dissolution. The ssa increase was faster for the smaller particle size sample, and the ratio between the ssa of the starting samples was not maintained during dissolution. Both micro- and mesopores were formed at different stages of the reaction for the two samples. Increasing ssa was also connected to the formation of a microcrystalline structure rich in Ca and P, as shown by TEM images. The segregation of both a SiO(2)-rich amorphous phase and a Ca/P-rich crystalline phase was observed after the first hour of dissolution. After 2 days of reaction, Ca/P-rich particles made of fine aciculate crystals were found either in close contact with SiO(2) particles or deposited on a small SiO(2)-rich core. A preliminary analysis of TEM data showed the formation, together with hydroxy carbonate apatite, of different types of calcium phosphates not detectable by powder X-ray diffraction.

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.

The adsorptive interaction of 1-butyne and 1-butene with a highly dehydrated pyrogenic silica system has been studied to understand the thermodynamic behavior of the adsorption process by the application of the Langmuir model and of the Van't Hoff equation. In situ FTIR spectroscopy allowed the characterization of the adsorption phenomenon in terms of involved surface sites, gas-volumetric determinations yielded quantitative information relative to the adsorption process, and microcalorimetric results allowed the comparison between calculated and experimental data. K(eq) and Delta(ads)G degrees were obtained from Langmuir's model application; Delta(ads)H data were obtained from the Van't Hoff equation and by the isosteric heats method and were compared with experimental values. The virtual constancy of Delta(ads)H with equilibrium pressure and surface coverage (Langmuir model) allowed us to obtain the Delta(ads)H degrees values and, consequently, the Delta(ads)S degrees values for the systems of interest.

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 ambient temperature adsorption of acetonitrile, in its perdeuterated form (CD3CN), was used for the surface characterization of both pure and sulfate-doped t-ZrO2. In most pure t-ZrO2 specimens, the absence of terminal and bi-bridged surface hydroxyls hinders completely the base-catalyzed CD3CN reactions which yield on other oxides either acetamide-like species or carbanionic surface species. In the case of sulfated t-ZrO2, even if some terminal hydroxyls are present, the mentioned surface reactions are hindered by the presence of acidic (sulfate) functionalities. On pure t-ZrO2, the predominant adsorbed species are represented by CD3CN molecules Lewis-coordinated to coordinatively unsaturated (cus) surface cationic sites. These sites are made available either by surface dehydration or by ligand-displacement of surface-coordinated (undissociated) water molecules. Lewis-coordinated CD3CN species dominate also on sulfated t-ZrO2, and the relevant adsorbing sites are made available both through the two m...

The present work deals with the physico-chemical characterization of the surface features of two powdery sol–gel-synthesized bioglass specimens (58S and 77S) employed in repair of human bones and soft tissues. In-situ transmission FTIR spectroscopy and adsorption microcalorimetry (with the use of water as a probe molecule) were adopted in parallel to study on one hand bioglasses (amorphous Si, Ca and P oxides) and on the other hand pure and doped silica specimens, as reference materials. It was observed that the presence of Ca and P moieties induces the formation of surface sites that possess higher strength and higher capability towards water coordination than do the hydroxy groups present on pure silica. In particular, the presence of some irreversibly coordinated water was observed both on these bioglasses and on doped silica. The Ca/P ratio seems to play a major role: (i) an excess of Ca induces the presence of coordinatively unsaturated surface (cus) Ca2+ ions, that generate Lewis acid sites that can strongly interact with water and can yield surface carbonates; (ii) the presence of P species increases the surface hydrophilic character and leads to the formation of Si–O–P labile bridges, which exhibit an enhanced propensity to dissociate water.

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.

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.

To check if the adsorption/desorption of 2,6-dimethylpyridine (2,6-DMP) is a suitable probe for the surface acidity of oxides, and to assign a band of controversial interpretation often observed upon 2,6-DMP adsorption, the ambient temperature uptake of 2,6-DMP on several oxidic systems was carried out. SiO2 was observed to yield a plain H-bonding interaction, characterized by an 8a band of adsorbed 2,6-DMP that is typical of silanols. Several (spinel) transition aluminas and the corundum α-alumina phase were examined and allowed to test the suitability of 2,6-DMP in distinguishing different types of surface Lewis acidity. Sulfated alumina and a β-zeolite in its H-form were used to check the sensitivity of 2,6-DMP uptake toward either induced or intrinsic Bronsted acidity and the possibility of observing (weak) Lewis-coordinated 2,6-DMP also in the presence of (strong) Bronsted-bound 2,6-DMP.

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.

The presence of lead in three-way converters (TWC) is considered to be one of the most important causes of catalyst deactivation: its poisoning effect has been ascribed to the irreversible interaction with the catalytically active metal supported on the washcoat, leading to the formation of stable inert alloys. This paper considers the lethal poisonous effect played by lead under certain conditions (e.g., at the high temperatures easily reached by a working catalyst) also on the alumina support (washcoat). The analysis was carried out on pure transition aluminas (A samples) and on Pb-containing alumina systems (APb samples). Structural and morphological studies were carried out by BET, XRD and (high-resolution) TEM, whereas surface features of pure and Pb-containing aluminas were analysed by in-situ FTIR spectroscopy. Data are reported for: (i) the adsorption of CO at room temperature (RT) (reveals strong Lewis acidity) and at 77 K (reveals total Lewis acidity); (ii) the RT adsorption of CO2 (reveals both Lewis acidity and, in the 1900–1200 cm−1 spectral region, surface basicity). It could be concluded that the presence of Pb on transition alumina supports does not modify appreciably the surface area nor the range of existence of the various crystal phases (i.e., there are no physical effects), but selectively eliminates both strong Lewis acidic properties, and basic properties of the alumina support (surface chemical effects).

The interaction of acetonitrile and adamantane–carbonitrile with hydroxy groups of zeolites causes changes in the OH stretching mode that render the zeolite surface IR-readable. Acetonitrile can penetrate inside the channels of medium-pore zeolites, while adamantane–carbonitrile (due to its larger molecular size) cannot. By using both IR probe molecules, discrimination between external and internal OH groups can be accomplished. The method is demonstrated by studying the interaction of the probe molecules with an H-ZSM-5 zeolite sample. Within the limits of experimental error, bridged Si(OH)Al groups (Bronsted acid sites) were all found to be located at the internal surface of the zeolite, while SiOH groups (silanols) were found to be mainly at external surfaces.

The ambient temperature adsorption of acetonitrile (in its d3 deuterated form, to avoid Fermi resonance band splitting in the analytical νCN spectral region) was studied on pure γ-alumina, γ-alumina doped with two different amounts of sulfates, γ-alumina doped with Ca, and a Ca-doped alumina that was thermally transformed into the δ,θ-alumina form. Acetonitrile adsorption readily reveals the different Lewis acidity due to different surface cationic species (e.g., Al3+ and Ca2+) but is only partly sensitive to the acid strength heterogeneity exhibited by Lewis sites due to the same cationic species (Al3+ ions, in the present case). Acetonitrile uptake perturbs all surface hydroxyl species that are free from H-bonding of the OH···OH type by either ligand insertion (the OH species at ∼3780 cm-1) or by (weak) H-bonding (the OH species at ∼3740 cm-1). When a plain H-bonding is formed, the relevant νCN mode is hardly distinguishable from that of a liquidlike physisorbed phase. The presence of large amounts of s...

Lewis acidic properties of transition aluminas whose surfaces have been doped with alkaline-earth metal cations (Ca2+ and Ba2+) were studied by means of the room temperature adsorption of carbon monoxide. The vibrational features of CO adsorbed at the surface of doped aluminas were investigated by IR spectroscopy in comparison with pure parent aluminas, while the quantitative and energetic features were studied by adsorption microcalorimetry. Various CO adspecies were found to form at the surface of both pure and doped-alumina, owing to the structural heterogeneity of the Al2O3 surface and to the presence of alkaline-earth metal cations. The surface heterogeneity was revealed by different vco stretching frequencies, namely vco≈2230, 2218 and 2205 cm−1 for coordinatively unsaturated tetrahedral Al3+ cations in different crystallographic configurations, and vco≈2186 and 2172 cm−1 for coordinatively unsaturated Ca2+ and Ba2+ cations, respectively. Heats of adsorption of ≈80, 70 and 55 kJ/mol were assigned to the formation of Al3+/CO complexes, ≈45 kJ/mol for Ca2+/CO and ≈30 kJ/mol for Ba2+/CO complexes. The latter value was estimated through a correlation curve existing between vco stretching frequencies and adsorption enthalpies. This correlation, already proposed in the past for CO adsorbed on non-d/d0/d10 metal cations, has been revisited and confirmed here, by including Al2O3 data for which an apparent lack of correlation between the two parameters was first observed. With respect to pure alumina, the population of Lewis acidic sites was found to be significantly depressed by the presence of alkaline-earth cus metal cations. These acidic sites are intrinsically weaker than tetrahedral cus Al3+ cations, as witnessed by smaller upward shifts of the vco stretching frequencies with respect to CO gas and lower heats of adsorption, in accordance with expectations from the charge/ionic radius ratios. Ca2+ cations were found to compete in adsorbing CO with Al3+ cations more efficiently than the larger Ba2+ cations. In the case of CaO/Al2O3 systems outgassed at 1023 K, a thin surface layer of calcium aluminate, not detected by XRD or HRTEM, was suggested to form.

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.

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.

Structure and morphology of ZrO 2 samples calcined at increasing temperatures have been examined by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), and the crystal planes most favorably exposed have been identified. Fourier transform infra-red (FTIR) spectroscopy has been used to describe the surface hydrated layer of the various samples, in which are present two types of OH groups and undissociated coordinated water molecules, and to extrapolate the surface hydrated layer of an ideal `perfect' monoclinic ZrO 2 system. Most of the surface features determined experimentally can be reproduced and explained by computer simulation of a regular crystal of monoclinic ZrO 2 cut along some of the crystal planes that were identified as most favorably exposed.

Several samples of m-ZrO2, characterized by different degrees of sinterization, were studied by FTIR and computer graphics. Crystallites of m-ZrO2 fired at high temperatures present a fairly regular termination, mostly along the (111) plane. When highly dehydrated, these materials adsorb CO in an ordered way, forming various surface CO clusters characterized by different degrees of dipole-dipole interaction. If CO2 is pre-adsorbed, surface carbonate-like species are formed which interrupt the ordered formation of CO clusters and the extent of the surface dipole-dipole interactions.

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.

In situ FTIR spectroscopy was employed to investigate some aspects of the ambient temperature (actually, IR-beam temperature) adsorption of acetone on various pure and sulfate-doped zirconia specimens. Acetone uptake yields, on all examined systems and to a variable extent, different types of specific molecular adsorption, depending on the kind/population of available surface sites: relatively weak H-bonding interaction(s) with surface hydroxyls, medium-strong coordinative interaction with Lewis acidic sites, and strong H-bonding interaction with Brønsted acidic centres. Moreover acetone, readily and abundantly adsorbed in molecular form, is able to undergo the aldol condensation reaction (yielding, as the main reaction product, adsorbed mesityl oxide) only if the adsorbing material possesses some specific surface features. The occurrence/non-occurrence of the acetone self-condensation reaction is discussed, and leads to conclusions concerning the sites that catalyze the condensation reaction that do not agree with either of two conflicting interpretations present in the literature of acetone uptake/reaction on, mainly, zeolitic systems. In particular, what turns out to be actually necessary for the acetone aldol condensation reaction to occur on the examined zirconia systems is the presence of coordinatively unsaturated O(2-) surface sites of basicity sufficient to lead to the extraction of a proton from one of the CH3 groups of adsorbed acetone.

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.

Transition phase aluminas have been used as catalysts, and their surface chemical properties have been studied for over 30 years. The various steps of the gradual comprehension of the surface structure and surface chemistry of aluminas are here summarized. Our main attention has been devoted to various aspects of the surface chemistry of aluminas, as revealed by the adsorption of selected probe molecules, rather than to a systematic description of the adsorption of the very many probe molecules used over the years. Among the various physico-chemical aspects of aluminas, some were thought to be of particular interest: solid (bulk) and surface vibrations, the surface hydrated layer, surface basicity and surface acidity. Whenever possible, a comparison between spectroscopic and quantitative data has been proposed.

The addition of CeO2 to Al2O3 supports and Al2O3-based catalysts leads to improved performance, that can be explained by surface chemical rather than structural morphological effects. Surface characterization of CeO2–Al2O3 systems has been carried out by in situ FTIR spectroscopy. The adsorption–desorption of pyridine as a surface probe allowed us to test for Bronsted acidity, never found, and the total Lewis acidity, which is higher for CeO2–Al2O3 systems than for pure Al2O3 supports. Several types of surface centres of different acidity could be identified, mainly by testing the competitive adsorptivity towards CO after stepwise desorption of pyridine at various temperatures. The adsorption of CO2 was used to test the basicity of CeO2–Al2O3 systems. The presence of CeO2, a basic oxide, does not modify appreciably the basic properties of Al2O3, on which a low concentration of rather weak basic centres is present, whereas the presence of Al2O3 tends to inhibit the high basicity typical of CeO2.

In catalysis, it has been suggested that the addition of CeO2 and other rare-earth metal oxides to alumina can stabilize the surface area and the spinel transition phases of the alumina support used in automotive catalysis. As this structural stabilizing effect by CeO2 was recently observed to occur only to a very limited extent, it was thought that the beneficial effect of CeO2 addition to Al2O3 supports would be useful for surface chemistry rather than structurally and morphologically. The surface characterization of several CeO2–Al2O3 systems has been carried out mainly by in situ FTIR spectroscopy and adsorption microcalorimetry. Specific OH groups bound to Ce surface cations are difficult to identify, but the usual OH profile of aluminas is modified by the presence of CeO2 to an extent that depends on CeO2 content and on activation temperature. Using CO as a surface probe molecule the surface Lewis acidity of the CeO2–Al2O3 mixed systems was characterized and it was revealed that CeO2 accumulates preferably on the flat patches of low-index crystal planes of the spinel structure, and that the presence of Ce cations stabilizes, also at high temperatures, the most acidic Lewis centres. The latter are constituted by coordinatively unsaturated Al ions with (incomplete) tetrahedral coordination and are probably located in crystallographically defective situations. Moreover, the presence of CeO2 brings about the formation of a family of Lewis-acid sites of medium strength, which are not present at the surface of bare (transition) aluminas.

The surface chemical features and sintering behaviour of two preparations of tetragonal zirconia (t-ZrO2) stabilized with 3 mol % Y2O3 have been examined, and have been compared with those of a 2 mol% t-ZrO2 preparation and a monoclinic zirconia (m-ZrO2) preparation.The adsorption of CO2 indicates that the most peculiar features of the genuine t-ZrO2 phase are: (i) the almost complete absence of surface hydrogencarbonates, related to the virtual absence of monodentate surface OH groups; (ii) the presence of various types of bidentate carbonates; and (iii) the formation of a peculiar monodenate carbonate species, characterized by a very small spectral separation between the coupled CO oscillators (and observed only on all t-ZrO2 preparations). In some stages of the thermal sintering process, some of the characteristics of t-ZrO2 become modified, and the surface chemical behaviour becomes similar to that of m-ZrO2. When metastable t-ZrO2 specimens start to segregate out an amorphous phase, which coats the crystallites, the adsorptivity towards CO2 declines sharply, and the usual carbonate-like species observed on most crystalline oxides no longer form.When CO2 is preadsorbed onto t-ZrO2, the overall capacity for CO uptake is decreased to a variable extent (15–50%), whereas the IR band corresponding to adsorbed CO is shiffed to higher wavenumbers by surface inductive effects only when CO2 yields appreciable amounts of surface hydrogencarbonate species.

Some soda-lime-phospho-silicate glasses, such as Hench's Bioglass(®) 45S5, form bone-like apatite on their surface when bound to living bone. To improve their osteointegration for clinical purposes, the fluoride insertion in their structure has been proposed, but we recently showed that fluoride causes oxidative damage in human MG-63 osteoblasts, via inhibition of pentose phosphate oxidative pathway (PPP) and its key enzyme glucose 6-phosphate dehydrogenase (G6PD). In the same cells we have now investigated the role of nitric oxide (NO) in these effects. Fluoride-containing bioactive glasses and NaF caused, as expected, release of lactate dehydrogenase in the extracellular medium, accumulation of intracellular malonyldialdehyde, inhibition of PPP and G6PD: we have now observed that these effects were significantly reverted not only by superoxide dismutase (SOD) plus catalase (scavengers of reactive oxygen species), but also by N-monomethyl l-arginine (l-NMMA, a NOS inhibitor) and 2-phenyl-4,4,5,5,-tetramethylimidazoline-1oxyl 3-oxide (PTIO, a NO scavenger). Moreover the two highest concentrations of both fluoride-containing bioglasses and NaF caused increase of nitrite (a stable derivative of NO) levels in the culture supernatant, which was inhibited by l-NMMA, erythrocytes, PTIO and SOD/catalase, and increase of intracellular NO synthase (NOS) activity. The incubation with bioglasses or NaF increased also the phosphorylation of Ser(1177) in the endothelial NOS isoform. Furthermore, the NO donor spermine NONOate was able to inhibit G6PD activity in vitro, and this effect was partly reverted by PTIO. Therefore our results suggest that most cytotoxic effects of fluoride are mediated by the production of NO: reactive oxygen species are important, causing NOS phosphorylation. We also observed, for the first time, that Tempol, but not SOD/catalase, besides inhibiting the oxidative stress induced by fluoride, also scavenges fluoride ions. For this reason it is not a selective inhibitor of the oxidative effects of fluoride.

Two Zn-doped sol―gel glasses with the same ZnO content (5 wt %; 4% mol) but different overall composition have been synthesized and characterized, in comparison with a bioactive Zn-free reference glass. The role of ZnO in modifying the bioactivity of sol―gel glasses was investigated by soaking the glasses in a simple tris(hydroxymethyl)aminomethane-buffered solution (TRIS-BS), so as to maximize the solubility and to minimize back-precipitation phenomena, which will depend only on the nature and concentration of dissolved glass components. Glass dissolution/ions release in TRIS-BS was monitored by ion coupled plasma emission spectroscopy, whereas modifications of surface composition upon reaction were checked by X-ray photoelectron spectroscopy (XPS). The deposition of a Ca―P layer and the consequent crystallization to hydroxy―apatite (HA) and/or hydroxy―carbonate―apatite (HCA) at the glass surface were investigated by X-ray diffraction and Raman, Fourier transform infrared (FTIR), and XPS spectroscopies. Glass dissolution rate, back-precipitation of silica gel, and formation/crystallization of an apatite-like layer on Zn-containing glasses were found to be either inhibited or delayed, according to the overall glass composition, in that the presence of the network former ZnO component enhances glass reticulation, with the consequent formation ofSi-O-Zn units. The presence of a ZnO component has no effect per se, but its influence depends on the overall composition of the glass and, in particular, on the CaO/SiO 2 and ZnO/CaO ratios, which determine the nature/structure of Zn and Ca surface species. Glass surface features were investigated by the combined use of in situ FTIR spectroscopy and adsorption microcalorimetry. The role played by surface Ca species, thought to be the most hydrophilic sites, was found to be a decisive factor in both glass dissolution mechanism and formation of an apatite-like surface layer: (i) the scarce dissolution in aqueous media of a (non bioactive) low-Ca and high-silica glass is due to the high reticulation caused by the scarce population of Ca 2+ cations in the role of network modifiers; and (ii) the amount of the latter species is, instead, much larger in the corresponding (moderately bioactive) high-Ca and low-silica glass, which dissolves more, although exhibiting a larger durability in aqueous solution than the Zn-free glass.

In vitro bioactivity features of a Ga-modified sol gel Si–Ca–P glass (SGGa) were investigated, in comparison with a plain ternary Si–Ca–P system (SG). Reaction/dissolution of the glass at increasing soaking times in simulated body fluids (SBF) and the consequent growth of an apatite-like layer, monitoring bioactivity, were studied by employing a variety of chemical and physical techniques. The growth of a crystalline apatitic layer at the Ga-modified-glass/SBF interface is severely delayed with respect to the Ga-free glass, and the reasons for it have been looked for in the dramatic changes induced, at the glass/SBF interface, by the presence of the Ga2O3 component. In situ Fourier transform infrared spectroscopy allowed to describe the nature/structure of surface terminations for the two glasses and to reveal/quantify the acidic strength of different Ga species exposed at the SGGa glass surface. 2,6-Dimethylpyridine and carbon monoxide were employed as molecular probes to reveal Bronsted and Lewis acidit...

Infrared and microcalorimetric data for the adsorption of CO onto a CaO/Al 2 O 3 system are reported, and related to the adsorption on pure Al 2 O 3 . The CO/Al 2 O 3 system is severely modified, as Ca 2+ ions accumulate at the surface of alumina, favouring the occupation of regular crystallographic terminations and gradually converting them into a bidimensional Ca aluminate layer. Unlike unsupported CaO, CaO/Al 2 O 3 adsorbs CO as linear complexes σ-coordinated onto coordinatively unsaturated Ca 2+ ions. Spectral and thermodynamic features of the CO/Ca 2+ complexes agree with the behaviour previously postulated for CO on non-d metal oxides.

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.

The every-day problem represented by the coexistence of several overlapped components in a narrow spectral range is treated. A home-made deconvolution program (Asymgrad) has been developed in order to deal with this problem. Asymgrad is able to perfom spectral deconvolutions into up to 13 peaks. The number of peaks, their analytical dependence and their symmetry can be defined by the user. The application of this software to some IR spectra of adsorbed species is presented and discussed in detail; particular attention is devoted to the description of the proper use of this complex deconvolution facility. Examples are reported showing the way to escape some deconvolution traps.

Two preparations of tetragonal zirconia (t-ZrO2) stabilized with 3 mol% Y2O3 have been characterized, and their features compared with those of a 2 mol% t-ZrO2 preparation and of a monoclinic zirconia (m-ZrO2) preparation.At ambient temperature, CO adsorption occurs only on surface cationic Lewis acid sites located in crystallographically defective configurations. The various t-ZrO2 preparations present several types of such defective sites, depending on the temperature of the sintering stage. The spectral features of the ambient-temperature interaction of t-ZrO2 with CO are complemented, on quantitative grounds, by gas-volumetric and microcalorimetric data. At high firing temperatures, amorphous phases start segregating from the t-ZrO2 crystallites, causing the ambient-temperature adsorptive capacity towards CO to decline.Upon CO adsorption at low temperaure (ca. 77 K), weaker adspecies form prevalently. These are ascribed to CO adsorption on cationic Lewis acid sites located in regular patches of low-index crystal planes, and to CO H-bonded to surface OH groups.Different t-ZrO2 preparations and differently sintered samples exhibit different particle sizes and various proportions of crystal surface defect sites vs. regular-face terminations: these differences are reliably monitored by CO adsorption patterns observed via IR spectroscopy, both at 300 and ca. 77 K.

The surface chemical features and sintering behaviour of two preparations of tetragonal zirconia (t-ZrO2) stabilized with 3 mol % Y2O3 have been examined, and have been compared with those of a 2 mol% t-ZrO2 preparation and a monoclinic zirconia (m-ZrO2) preparation.The adsorption of CO2 indicates that the most peculiar features of the genuine t-ZrO2 phase are: (i) the almost complete absence of surface hydrogencarbonates, related to the virtual absence of monodentate surface OH groups; (ii) the presence of various types of bidentate carbonates; and (iii) the formation of a peculiar monodenate carbonate species, characterized by a very small spectral separation between the coupled CO oscillators (and observed only on all t-ZrO2 preparations). In some stages of the thermal sintering process, some of the characteristics of t-ZrO2 become modified, and the surface chemical behaviour becomes similar to that of m-ZrO2. When metastable t-ZrO2 specimens start to segregate out an amorphous phase, which coats the crystallites, the adsorptivity towards CO2 declines sharply, and the usual carbonate-like species observed on most crystalline oxides no longer form.When CO2 is preadsorbed onto t-ZrO2, the overall capacity for CO uptake is decreased to a variable extent (15–50%), whereas the IR band corresponding to adsorbed CO is shiffed to higher wavenumbers by surface inductive effects only when CO2 yields appreciable amounts of surface hydrogencarbonate species.