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Nanoparticles research represents one of the most active fields in science due to the importance of nanosized materials in a wide variety of applications. Their characterization needs the comparison of data coming from different experimental techniques, but the peculiar properties of the nanosystem that each technique points out are not always properly taken into account and misleading results have been often reported. In this work, we generated transmission electron microscopy like (TEM-like) data to predict the extended X-ray absorption fine structure (EXAFS) and chemisorption-like typical outputs as the average coordination numbers up to fourth shell of the particles distribution and the surface area. The aim of the simulations is to explore the dependence of the calculated average coordination number (ACN) and average dispersion (AD) values from each parameter characterizing a particle size distribution (PSD), as the mean diameter, the width, the shape, and the profile, and shows that a range of distr...

In two recent contributions [PCCP 12 (2010) 5605; Dalton Trans. 39 (2010) 8437], we combined in situ and in operando XANES/EXAFS, CO chemisorption and catalytic tests to elucidate the role that dopants (LiCl, KCl, CsCl, MgCl2 LaCl3) have in the nature, relative fraction, reducibility, and dispersion of Cu-phases on CuCl2/γ-Al2O3 catalysts for C2H4 oxychlorination reaction, a key step of PVC chemistry. In the present work, we extend these studies by investigating the effect that the dopants have on the nature, population, and strength of surface Lewis and Bronsted sites of the support, using IR spectroscopy of adsorbed CO at liquid nitrogen temperature. The doping eliminates all the surface Lewis acidity in CsCl- and KCl-doped catalysts and strongly suppresses it in the remaining cases. The increase of the strength of the Bronsted sites is remarkable in all cases but the CsCl-doped one. To understand both the effect of Cl- anions and dopant cations a set of dopant free, HCl-impregnated and of Cu-free dopant-impregnated supports have been investigated. Addition of chlorine decreases the density and the strength of Lewis sites, while it increases those of the Bronsted sites. Catalytic testing of each material revealed that formation of chlorinated by-products was directly correlated with the density of Lewis acid sites. Furthermore, an empirical correlation was found between the strength of the Bronsted acid sites of the support and the stretching frequency of CO adsorbed on the reduced fraction of the active copper chloride phase. The present study is aimed to complement the published literature on alumina, underlining the usefulness of the molecular approach made by IR spectroscopy low temperature adsorbed CO to investigate the surface of catalyst support.

International audience; Adsorption of N-2 at 77 K and scanning electron microscopy have been used to measure the changes in the support morphology, at nano- and microscale level, along the processes involved in the preparation of a supported Pd catalyst: Pd deposition, doping, and thermal treatments. Among the investigated supports, viz., activated carbons, gamma-Al2O3, SiO2, and SiO2-Al2O3 (SA), the SA one was found particularly sensitive to these processes, as a result of its high plasticity and reactivity. Involved processes can be summarized as follows: (i) During the I'd deposition, the support itself is partially dissolved and removed as a result of both the basicity of the precipitating agent and the final washing. (ii) When the undoped sample is thermally treated up to 823 K, only modest phenomena are observed. (iii) Upon doping with potassium carbonate, the support dissolution continues, and the greater the carbonate concentration, the greater the dissolution extent. In this case the dissolved material is not removed, but reprecipitates (partially outside the pores), during the subsequent drying at 393 K. (iv) When doped samples are thermally treated, the reaction between carbonate and support causes the mobilization of the support itself, with sintering phenomena that can reach the total collapse of the porous structure. The starting temperature of the pore collapse decreases with increasing potassium carbonate concentration. The modification of the support influences, directly or indirectly, the surface properties and the availability of Pd particles that can be doped or even covered by materials from support and made more or less accessible or even inaccessible by pore narrowing, widening, or blocking.

International audience; Activated carbons are widely used as supports for industrial catalysts based on metal nanoparticles. The catalytic performance of carbon-supported catalysts is strongly influenced by the carbon activation method. Notwithstanding this important role, the effect induced by different activation methods has been rarely investigated in detail. This work deals with two carbons of wood origin, activated either by steam or by phosphoric acid, and the corresponding catalysts based on supported Pd nanoparticles. We demonstrate that the catalysts perform in a different way in hydrogenation reactions depending on the nature of the carbon used as a support, being the palladium dispersion the same. We propose a multi-technique approach to fully characterize both carbons and catalysts at the micro-and nanoscale. In particular, we investigate how the activation procedure influences the texture (by N-2 physisorption), the morphology (by Scanning Electron Microscopy), the structure (by Solid State Nuclear Magnetic Resonance, Raman spectroscopy and X-ray Diffraction) and the surface properties (by X-ray Photoelectron Spectroscopy, Diffuse Reflectance Infrared Spectroscopy and Inelastic Neutron Scattering) of carbons and of the related catalysts. The comprehensive characterization approach proposed in this work allows the rationalization, at least in part, of the role of activated carbons in enhancing the performance of a hydrogenation catalyst

A complete catalytic cycle was performed on CuCl2/Al2O3 catalyst for ethylene oxychlorination at 500 K. X-ray absorption near-edge spectroscopy, extended X-ray absorption fine structure, electron paramagnetic resonance, and IR of adsorbed CO were used to demonstrate that the ethylene oxychlorination reaction, C2H4+2HCl+1/2 O2→C2H4Cl2+H2O, follows a three-step mechanism: (i) reduction of CuCl2 to CuCl (2CuCl2+C2H4→C2H4Cl2+2CuCl), (ii) oxidation of CuCl to give an oxychloride (2CuCl+1/2 O2→Cu2OCl2), and (iii) closure of the catalytic circle by rechlorination with HCl, restoring the original CuCl2 (Cu2OCl2+2HCl→2CuCl2+H2O). The dispersing/sintering effect of the different reagents on the active phase has been also investigated.

Alumina supported CuCl2, the basic catalyst for ethylene oxychlorination, has been investigated by UV-Vis spectroscopy, EPR, EXAFS and XANES in a wide range (0.25-9.0 wt%) of Cu concentration. We have evidenced that, at low Cu content, the formation of a surface aluminate species takes place. The formation of this surface copper aluminate stops at 0.95 wt% Cu / 100 m2; at higher Cu concentrations excess copper chloride precipitates directly from solution during the drying step forming an highly dispersed CuCl2.H2O, phase, overlapping progressively the surface aluminate. Depletion tests and IR spectroscopy of adsorbed NO have demonstrated that the latter is the only active phase. A complete catalytic cycle has then been performed on CuCl2/Al2O3 catalyst. EPR, XANES and EXAFS, have been used to demonstrate that the ethylene oxychlorination reaction: C2H4 + 2HCl + ½ O2 --> C2H4Cl2 + H2O follows a three steps mechanism: (i) reduction of CuCl2 to CuCl (2CuCl2 + C2H4 --> C2H4Cl2 + 2CuCl), (ii) oxidation of CuCl to give an oxychloride (2CuCl + ½ O2 --> Cu2OCl2) and (iii) closure of the catalytic circle by rechlorination with HCl, restoring the original CuCl2 (Cu2OCl2 + 2HCl --> 2CuCl2 + H2O). Finally, we have shown that time resolved, in situ, spectroscopy is a very promising technique to investigate the interplay between catalyst activity and oxidation state of copper.

The conversion of ethylchloride into ethylene+HCl on pure and doped alumina supports and on CuCl 2 –Al 2 O 3 -based oxychlorination catalysts has been investigated by pulse reactor and FT-IR spectroscopy. FT-IR spectra of ethylchloride adsorbed on γ-Al 2 O 3 show weakly molecularly adsorbed species and ethoxy groups formed by nucleophilic substitution. Additionally, adsorbed diethylether is also observed. The analysis of the gas-phase species shows that ethoxy groups decompose, giving rise to ethylene at 523 K. Under the same conditions, gaseous HCl is also released from the surface and diethylether is also observed in the gas phase. Chlorination of alumina with HCl only partially hinders the dehydrochlorination mechanism occurring through ethoxy groups. Experiments performed on alumina doped with MgCl 2 and KCl indicate that the site reactivity scale for EtCl conversion to ethylene is the following: bare Al 2 O 3 >CuCl 2 on Al 2 O 3 >MgCl 2 on Al 2 O 3 >KCl on Al 2 O 3 . Doping with MgCl 2 and in particular with KCl limits the activity of the bare support in the dehydrochlorination. These data strongly support the previous proposal that the exposed alumina surface catalyzes the dehydrochlorination of EDC to VCM, with a consequent loss in selectivity in the oxychlorination reactor. The beneficial effect of doping with KCl and MgCl 2 is due to the reduced dehydrochlorination activity.

The effect of aging and heating treatments up to 500 K on alumina-supported CuCl2, i.e., the base catalyst for ethylene oxychlorination, has been investigated by UV‐vis spectroscopy, a solubility test, EXAFS, XRD, and EPR in a wide range (0.25‐9 wt%) of Cu concentration. It is shown that the catalyst undergoes significant changes with both time and thermal treatments, so accounting for some contradictory results reported in the literature. While the surface Cu aluminate (formed during impregnation) does not change upon aging and heating, supported CuCl2 (precipitated from impregnating solution during the drying process) undergoes a slow hydrolysis reaction with the formation of paratacamite and HCl. The HCl formed during the hydrolysis reacts with the alumina surface with the formation of >Al‐Cl species. Upon heating, the initially formed paratacamite can react with surface >Al‐Cl species with nearly total restoration of CuCl2, which is consequently the main species present on the catalyst at the beginning of the oxychlorination reaction. The obtained picture is able to explain the results emerging from activity tests on the whole set of catalysts, indicating that surface aluminate is not active and that the active phase is CuCl2. c ∞ 2000 Academic Press

CuCl 2 /Al 2 O 3 ethylene oxychlorination catalysts have been characterized by using IR spectroscopy of the surface hydroxy-groups and of adsorbed pyridine and CO 2 . The ethylene oxychlorination reaction to 1,2-dichloroethane has been investigated by using pulse reactor studies and in-situ IR experiments in static conditions. The results allowed emphasizing the negative role of uncovered alumina surface, evidenced by IR experiments, considered to be responsible for the dehydrochlorination of 1,2-dichloroethane with a consequent loss in selectivity that is very important in low Cu-loading samples.

The origin, the classification and the effect on catalytic performance of pore texture of heterogeneous catalysts are briefly examined. The techniques and the methods suitable for the determination of related properties (surface area, pore volume and pore size distribution) are reviewed. Particular attention is paid to the most widely used ones: vapour adsorption at low temperature, mercury porosimetry, incipient wetness impregnation and picnometry. Advantages, disadvantages and applicability of each method to different pore textures are pointed out. The best choice of a group of methods, allowing a complete characterization of catalysts, is proposed.

The effect of pre-reduction in solution with chemical reagents on the catalytic performance and catalyst properties of Pd/carbon catalysts was systematically investigated with a multitechnique approach. The results are critically discussed in comparison to those recently obtained on analogous Pd/alumina catalysts. It was proved that the Pd phase on the carbon surface is characterized by a high mobility, opposite to what occurs on alumina. As a result, the Pd particles on carbon aggregate together during pre-reduction, with a consequent decrease in available metal surface. Pd particles remain aggregated also in reaction conditions; the decreased Pd dispersion negatively affects the catalyst activity in the debenzylation of 4-benzyloxyphenol.

The most remarkable difference between catalysis during the 50s and 60s and nowadays is the remarkable development of characterization techniques. Various factors contributed to that growth: (i) need of having a better control on the catalyst in order to meet the requirements for further optimization of processes already in operation and/or for realization of new processes; (ii) appearance of new classes of solids with catalytic properties and peculiar characteristics (zeolites, zeolite-like materials, oxides with controlled porosity, very high pore volume silica, superacids, etc.); (iii) technology and computer development have placed on the market more powerful and friendly to use versions of known techniques (FT-IR, FT-Raman, calorimeter, etc.) or new techniques, often initially developed for other sectors use (XPS, EXAFS, SIMS, ISS, EPMA, etc.). To realize how large is the growth of the characterization influence in the development of catalysts it is enough to look at scientific magazines and catalysis congresses proceedings. Because of the tremendous variety of disposable techniques it is impossible to review all of them in few pages. So we have to decide what techniques to describe and what to treat deeply. The choice has been done on the basis of: (i) applicability to real catalysts (so spectroscopies on single crystals like LEED, UPS, etc. were rejected); (ii) easy access, either in cost and/or in necessary facilities (however also techniques both expensive like XPS, NMR, TEM and of difficult access like EXAFS, requiring synchrotron radiation, will be reported because of their importance); (iii) applicability to many different systems (then little space will be devoted to Miissbauer and PAS, much more to N, adsorption, IR spectroscopy and temperature programmed techniques, etc.); (iv) informative content, or capacity to give a manifold information (multipurpose techniques like IR spectroscopy are preferred). On the whole 35 techniques, i.e. a number enough to face adequately nearly all the problems of daily practice, are described; on a few other (about 20) a short description is given. For all of them an adequate bibliography useful for a first deepening will be given. Techniques have been grouped on the basis Of: 1. morphology and physical characteristics, 2. surface characteristics

While the most frequently used characterization techniques in catalysis have been described in the first part of this paper, in this part the application of the techniques to the solution of practical problems is described.

The application of IR, Raman, UV–visible, EPR, XANES, EXAFS, and TPR techniques to the determination of the Fe 3+ local environment in Fe-silicalite is described and discussed. These methods give information concerning the structural changes of the zeolitic structure, upon thermal treatments and interaction with adsorbates. In particular the effect of template burning at 773 K or at 973 K on the local Fe 3+ environment has been discussed in detail. The reactivity of the zeolite towards NH 3 has also been considered.

The effects on the local environment of metal centres in Ti- and Fe-silicalites, induced by a vacuum treatment and by subsequent NH3 dosage, has been studied by means of XANES and UV-vis spectroscopies. The Ti(IV) environment is mainly tetrahedral in vacuo and becomes octahedral after interaction with NH3. Fe(III) is in tetrahedral coordination in presence of adsorbates, while in vacuo it is in a distorted tetrahedral symmetry. These conclusions are qualitatively supported by IR and Raman data.

The change in structural and surface properties of Pd/Al2O3 catalysts as the effect of reduction in liquid phase during preparation is investigated by a multi-technical approach. It has been found that, although the treatment leaves an external shell of oxidized Pd because of the exposure to air of final wet catalyst, it affects both the catalyst reducibility and the properties of the supported Pd nanoparticles, in terms of dispersion, particle size, morphology, interaction with the support, structural order, and surface properties. Consequently, unreduced and pre-reduced catalysts show different performances in the debenzylation of 4-benzyloxyphenol reaction.

In this work a comparison is made between values of the metal surface areas of several alumina-supported Ru, Rh, and Pt catalysts obtained by hydrogen adsorption isotherms, here defined as the “Multiple Introductions” method, and those calculated by a very simple technique defined as the “Single Introduction” method. With the systematic application of the procedure designated “Back-Sorption,” particularly good agreement is observed between the two techniques if dispersion is calculated on the basis of the irreversibly adsorbed hydrogen. “Back-Sorption” is a necessary practice because of the presence on the above-mentioned metals of more than one adsorbed species not to be considered for the calculation of dispersion, as shown in a more detailed manner for a Pt Al 2 O 3 catalyst using temperature-programmed desorption. Whenever the conditions for its applicability are satisfied, the Single Introduction method provides a faster and more reliable way to measure the dispersion of metal-supported catalysts than the Multiple Introductions technique.

X-ray absorption at the Ti K edge (both XANES and EXAFS) of a very pure Ti-silicalite containing a small fraction of Ti(IV) substituting Si(IV), has been performed in order to study the effect of the presence or absence of ligands such as H2O and NH3 on the Ti(IV) coordination sphere. In particular, the effect of an outgassing treatment at 400 K and of the interaction with NH3 has been studied and described in detail. It has been found that the Ti(FV) is fourfold coordinated in the samples outgassed at 400 K and expands its coordination sphere number under the action of adsorbates.

The understanding, at the atomic level, of the role played by additives (dopants or promoters) in the chemistry of an industrial catalyst is a very complex and difficult task. We succeeded in this goal for the ethylene oxychlorination catalyst (CuCl(2)/gamma-Al(2)O(3)), used to produce dichloroethane, a key intermediate of the polyvinyl chloride chemistry (PVC). Among the most used additives for both fluid and fixed beds technologies (LiCl, KCl, CsCl, MgCl(2), LaCl(3), CeCl(4)) we have been able to highlight that KCl, and CsCl, forming in reaction conditions a mixed phase with CuCl(2), strongly modify the catalyst behaviour. In particular, these additives are able to displace the rate determining step from the CuCl oxidation (undoped catalyst) to the CuCl(2) reduction. This results from the decrease of the rate of the latter reaction, thus the overall activity of the system. For all remaining additives the rate determining step remains the CuCl oxidation, as for the undoped catalyst. These results have been obtained coupling the catalyst activity monitored with a pulse reactor working in both non-depletive and depletive modes with time resolved XANES spectroscopy performed under in operando conditions (i.e. coupled with mass spectrometry). Formation of CuK(x)Cl(2+x) and CuCs(x)Cl(2+x) mixed phases has been proved monitoring the Cu(II) d-d transitions with UV-Vis spectrometer and the CO stretching frequency of carbon monoxide adsorbed on reduced catalyst by in situ IR spectroscopy. Finally, of high relevance is the observation that the fully oxidized catalyst is inactive. This unexpected evidence highlight the role of coordinatively unsaturated Cu(I) species in adsorbing ethylene on the catalyst surface indicating that copper, in the working catalyst, exhibits a (I)/(II) mixed valence state.

The preparation by the deposition-precipitation method (using Na(2)PdCl(4) as a palladium precursor and Na(2)CO(3) as a basic agent) of Pd catalysts supported on gamma-Al(2)O(3) and on two different types of active carbons has been followed by several techniques (UV-vis, EXAFS, XRPD, and TPR). This work consists of four successive parts: the investigation of (i) the palladium precursor liquid solution (in the absence of substrate), (ii) the solid precipitated phase (in the absence of substrate), (iii) the precipitated Pd(2+)-phase on the supports as a function of Pd loading from 0.5 to 5.0 wt % (i.e., the final catalyst for debenzylation reactions), and (iv) the Pd(0)-phase formed upon reduction in H(2) atmosphere at 393 K. A time/pH-dependent UV-vis experiment indicates that Pd(2+) is present in the mother solution mainly as PdCl(2)(H(2)O)(2)] and [PdCl(H(2)O)(3)](+). Upon progressive addition of NaOH (3.0pHapproximately 3.8), the concentration of the two complexes is almost constant and then they rapidly disappear because of the precipitation of an amorphous aggregation of Pd(2+)-polynuclearhydroxo complexes. This phase represents a model material for the active supported phase. Thermal treatments at increasing temperature of this phase cause progressive water loss and resulted in a progressive increase in crystallinity typical of a defective PdO-like phase. The EXAFS spectrum of the final catalysts has been found to be intermediate between that of the unsupported amorphous Pd(2+)-polynuclearhydroxo complexes and that of the PdO-like phase. Independent of the support, EXAFS was not able to evidence any fraction of reduced metallic Pd, meaning that all Pd is in the 2+ oxidation state within the sensitivity of the technique (a few percent). Analogously, independent of the support, XRPD was not able to detect the presence of any crystalline supported phase. The Pd local environment of the as-precipitated samples changes slightly as a function of Pd loading from 0.5 to 2.0 wt %: at higher loadings, no further modification has been observed. After reduction in an H(2) atmosphere, two trends have been observed: (i) the dispersion of Pd nanoparticles tends to decrease with increasing Pd concentration, less significantly on Al(2)O(3)-supported samples and more significantly on carbon-supported ones and (ii) the dispersion depends on the carrier following the sequence Al(2)O(3)CpCw according to the increasing palladium-support interaction strength.

The changes in the support morphology, at nano- and micro-scale level, have been investigated along the two-step processes involved in the preparation of a Pd supported on SiO 2 -Al 2 O 3 (SA) catalyst: Pd deposition and K 2 CO 3 doping. During the latter step part of the support dissolves and re-precipitates (partially outside the pores) covering the Pd particles. XRPD shows a significant rearrangement of the support at the long range order scale, while 29 Si and 27 Al solid-state (SS) NMR indicate that the average local environment around both Si and Al atoms remains unaltered.

The preparation by a deposition-precipitation method (using Na2PdCl4 as palladium precursor and Na2CO3 as basic agent) of Pd catalysts supported on γ-Al2O3 and on two different types of activated carbons has been studied by EXAFS and TPR as a function of Pd loading from 0.5 to 5.0 wt%. Independently from the support, neither reduced metal fraction nor crystalline phase has been observed. EXAFS shows that the Pd local environment of the final catalysts changes slightly as a function of the Pd loading from 0.5 to 2.0 wt%: at higher loadings no further modification has been observed.

The physical properties (microcrystal morphology, crystallinity, internal perfection, adsorptive capacities toward CO and N 2 , and IR manifestations of the skeletal modes and of the hydroxyl groups) of a Na- and Al-free silicalite (S) prepared following a specifically designed method are investigated. Comparison is made with the silicalite containing Na and Al impurities prepared following a more conventional (classical) path (SNa)

In paper 1 we have shown that the structural properties of silicalites depend upon the preparation procedure. In particular Na- and Al-free sample (S) prepared following a specifically designed method is characterized by the presence of internal atomic-dimension defects (nanodefects and microcavities). On the basis of spectroscopic data and computer graphic simulations, it is shown that the microcavities derive from one or more missing [SiO 4 ] units and can contain up to four OH groups per missing tetrahedron

This work is devoted to understand the effect of K-doping (from K2CO3) on the reducibility, sintering, and surface properties of Pd metal nanoparticles deposited on a peculiar high surface area SiO2–Al2O3 (SA) support. The effect of K-doping on the Pd/SA catalyst is systematically investigated by means of several complementary techniques (TPR, TEM, CO chemisorption and FTIR spectroscopy), trying to separate the effects of the doping loading (spanning the large 0.25–20.3 K/Pd atomic ratio interval), of the activation temperature (up to 823 K) and of the activation atmosphere (air or H2). It is shown that the presence of dopant, already at the lowest loading, causes an important increase of the PdO reduction temperature. The sulphur poisoning released from the support in the undoped sample during the thermal treatments in H2 atmosphere is inhibited in the presence of K2CO3. The dramatic loss of metal area measured by CO chemisorption for samples H2-treated at high temperature is not justified by the small particle sintering observed by TEM, and is assigned to the progressive particle encapsulation due to the mobilization of the support by reaction between carbonate and support itself. FTIR spectroscopy of adsorbed CO, allowing to probe the nature of the Pd surface available for adsorption, confirms the hypothesis.

The preparation of a Pd/C catalysts for hydrogenation reactions has been followed with different techniques in all its key steps: precursor precipitation from solution, partial reduction from the support, chemical reduction and, to complete the process for sake of study, H2 reduction.

By diluting optically opaque carbon-supported Pd particles in silica Aerosil® we succeeded in observing the IR bands of adsorbed carbonyls and extracting information on the particle dispersion. Comparison with literature single crystal data and with silica–alumina supported Pd allowed us to make an assignment in terms of linear and 2-fold bridged carbonyls formed on Pd(111) and Pd(100) faces. Two Pd/C samples have been investigated. The relative intensities of the two carbonyl families observed on the two samples are consistent with the Pd dispersion independently measured with CO chemisorption, TEM and EXAFS analysis.

We present a methodology that allows us to extract quantitative information from EXAFS data collected on complex samples where the absorbing species is present in more than one phase. We have chosen as our case study the CuCl2/Al2O3 material, which represents the basic catalyst for the ethylene oxychlorination reaction (a fundamental intermediate step in PVC production). In previous studies [J. Catal. 2000, 189, 91, and J. Catal. 2000, 189, 105], it has been shown that three different copper species are present on CuCl2/Al2O3a Cu-aluminate phase, a highly dispersed copper chloride phase, and an aggregated paratacamite (Cu2(OH)3Cl) phase, whose relative fraction depends on copper loading, sample aging, and heating conditions. In this work, we extract from the EXAFS spectra the fraction of the three phases on a quantitative ground. A study of the corresponding XANES spectra allows us to qualitatively support the EXAFS results. This methodology represents a generalization of the standard EXAFS procedure that...

International audience; Activated carbons arematerials with relevance in different industrial applications. Due to the inherent complexity and heterogeneity of their structures, an easy assignment of the species present on their surface has a challenging result. Only recently, with the possibility to collect well-resolved inelastic neutron spectra and to simulate by DFT methods more or less extended graphitic clusters, this task is starting to become feasible. Here we report our investigation on a steam activated carbon and we show that different vibrations in the region of out-of-plane C-H bending modes are specifically connected to hydrogen terminations belonging to extended and regular borders or to short and defective ones. Furthermore, simulations including heteroatoms such as oxygen allowed us to point out spectral regions with a contribution from carboxyl species

CuCl 2 on γ-alumina, the base catalyst for oxychiorination reactions, has been investigated by several techniques as a function of Cu loading, sample aging and heating. The results point out the formation of a surface Cu aluminate species and a highly dispersed CuCl 2 . The latter slowly hydrolyzes under aging, but CuCl 2 is restored under heating and is the active species in oxychiorination as demonstrated by activity tests.

CuCl 2 /Al 2 O 3 based ethylene oxychlorination catalysts have been characterized by using JR spectroscopy of the surface hydroxy-groups and of adsorbed pyridine and CO 2 . The ethylene oxychlorination reaction to 1,2-dichloroethane and the dehydrochlorination of ethylchloride (chosen as a probe molecule) have been investigated by using both pulse reactor measurements and in-situ JR experiments in static conditions. Experiments performed over doped alumina and doped CuCl 2 /Al 2 O 3 confirmed that the exposed support surface can be responsible of the dehydrochlorination of 1,2-dichloroethane (EDC) to vinyl chloride monomer (VCM), with a consequent loss in selectivity in the oxychlorination reactor. Doping alumina with MgC1 2 and in particular with KC1 limits the activity of the bare support in this side-reaction.

Publisher Summary Silicalites and Al-substituted Silicalites are characterized by substantially identical optical UV-Vis and EPR spectra. Substitution of Si with a variety of heteroatoms can cause dramatic changes in the spectroscopic properties of the zeolite. Fe-Silicalite has been studied by means of optical (DRS UV-Vis, IR Raman) and EPR spectroscopies to characterize the coordination state of framework species and to identify the presence of extraframework species (isolated and clustered). It is found that the ratio between framework and extraframework Fe species is strictly related to the sample calcination procedure. Probe molecules like CO, NO, and NH3 prove their utility to characterize the properties of this material, through interaction with Brensted and Fe sites and formation of adducts having simple vibrational properties.

The influence of the synthesis parameters over the physico-chemical features of poroussilica gels derived from tetraethyl orthosilicate has been studied using nitrogen adsorption and FT-IR. Under acid conditions long shaped siloxane particles were produced and microporous amorphous silicas with high surface area were obtained. These samples showed a relatively high concentration of H-bonded and/or “internal” hydroxy groups. The base-catalyzed samples exhibited features of colloidal gel and mesoporous amorphous materials were obtained. The structure is characterized by relatively low surface area with a monomodal porosity. These silicas have an high concentration of the free surface silanol groups. The acid-catalyzed samples resulted completely inactive in the ammoximation reaction, while the base-catalyzed silicas were active in the same reaction.

The synthesis of hydroxylamine by oxidation of ammonia with hydrogen peroxide on titanium based catalysts is reported. Titanium silicalite is the best catalyst for the reaction. The influence of some reaction parameters on the main and side reactions is discussed and the reaction network is proposed. The role of titanium is pointed out by results of spectroscopic studies.

In a series of combined adsorption, reactivity and spectroscopic experiments in solution with ketones of different size and shape, the fundamental role of the hydroxylamine pathway in the cyclohexanone ammoximation is established. In presence of H 2 O 2 and NH 3 , framework Ti(IV) forms octahedrally distorted aquohydroperoxo and ammonia-hydroperoxo mixed complexes: the latter one being the precursor of the hydroxylamine formation. This intermediate immediately reacts with cyclohexanone in the channels or diffuses to the external solution where it gives oximation reaction with larger ketones which could not penetrate the channels.

The most important spectroscopic features in the UV-Vis of framework and extraframework Ti(IV) in titanium silicalite are briefly summarized. The spectroscopic manifestations of the complexes formed by framework Ti(IV) in presence of H2O2 are reported. The formation of EPR active species is also considered.

Nests of OH groups localized at defective positions inside the silicalite framework can react with chromic acid to give grafted chromate (and/or dichromate) species. Successive reduction in CO yields mainly Cr(II) species anchored to the framework, which upon CO and/or NO dosage form well-defined polycarbonylic, polynitrosylic, and mixed CO/ NO complexes fully characterized by IR spectroscopy. The grafted Cr(II), and possibly Cr(III), ions are efficient centres for ethylene polymerization. Time-resolved IR spectra show that the polymeric chains formed inside the silicalite channels are short and have spectroscopic features different from those of the longer chains formed on the external surface.

The application of UV-Vis diffuse reflectance, IR transmission, Raman and ESR spectroscopies to the determination of extraframework and framework Ti in Titanium-silicalite is discussed in detail. The four methods give complementary information. In particular the utility of the UV-Vis and Raman spectroscopies to detect extraframework Ti is definitely established, while IR proves to be more useful for framework Ti. ESR spectroscopy can be also utilized on reduced samples to distinguish between the two types of Ti.

Summary Sorption measurements of small (N 2 ) and large (i.e. xylenes) probe molecules together with spectroscopic and diffractometric techniques have been used to characterize the porous structure of Ti-silicalite before and after thermal treatments in the range 823–1573K. It is noticeable that N 2 and p-xylene adsorption are correlated to the zeolite framework while m-xylene uptake depends on the content of Ti in the framework. The results also indicate that the Ti extraction from the lattice during the thermal treatments begins before the framework collapse.

Summary The synthesis of Ti silicalite was studied in a sealed silica tube via a dry impregnation of a preformed microspheroidal porous silica with a solution containing TPAOH and a soluble alkyltitanate. In few hours the crystallization proceeds towards the formation of the zeolite having substantially all Ti included in the framework. Extra structural Ti appears only in long time synthesized products.

The IR band at 960 cm−1 observed on TS is due to a local stretching mode of a [TiO4] unit in the silicalite framework. Framework Ti does not show Lewis acidity as probed by CO adsorption at 77 K. TiOH and SiOH have undistinguishable IR properties. At 77 K they form with CO very weak 1:1 OH…CO adducts. Small amount of extralattice Ti in form of TiO2 can be probed by CO adsorption at 77 K.

The stability and deactivation behavior of Ti-silicalite employed as a catalyst in the ammoximation of cycloexanone to cycloexanonoxime have been investigated. The reaction was performed in liquid phase using H2O2 as an oxidizing agent. The solid was characterized by various techniques: chemical analysis, thermogravimetry, IR and UV-Vis spectroscopy, XRD, gas adsorption and a Standard Activity Test. Three main deactivation processes are identified: (i) slow dissolution of the framework with accumulation of Ti on the external surface of the remaining solid; (ii) direct removal of Ti from the framework and (iii) pore filling by by-products.

As a part of a research devoted to selective oxidation of organic compounds, we have studied the synthesis of cyclohexanonoxime by direct ammonia oxidation in presence of cyclohexanone. By using titanium silicalite as catalyst the reaction took place in a smooth and selective way. The effect of the most important experimental conditions was investigated. The role of the catalyst and some possible reaction mechanisms were discussed. Our results provided a promising starting point for the development of a new technology for cyclohexanonoxime synthesis.

A systematic investigation of the IR and Raman spectra of pure and Al-, B-, Ti- and Fe-substituted silicalites in the SiO stretching region (1500–700 cm–1) is presented. As well as the characteristic stretching modes of the skeleton, silicalites containing hydroxylated nests show also broad bands at ca. 960 cm–1(IR) and at ca. 976 cm–1(Raman), associated with O3Si—OH group modes, with prevailing Si—OH stretching character. The replacement of Si with heavier elements (like Ti or Fe) causes the appearance of new IR- and Raman-active modes (i) at 960 cm–1(IR and Raman) and at 1127 cm–1(Raman) in Ti silicalite; (ii) at 1015 cm–1(IR) and at 1020 cm–1(Raman) in Fe silicalite. Neither the Raman nor the IR spectra of the skeletal modes are substantially modified by the introduction of Al (ZSM5). The presence of boron induces the appearance in the IR spectra of a complex absorption at 1380 cm–1 and at 960–930 cm–1, which corresponds to the absorptions at 1417 and 976 cm–1 in the Raman spectra. The assignment of the absorptions associated with heteroatoms and hydroxylated nests is discussed in detail.

The crystallization of ZSM—5 zeolite, from a 3.6 Na 2 O, 6.6 TPA-Br, 1 Al 2 O 3 , 24.0 SiO 2 , 180 H 2 O system at 120°C, proceeds through various steps which have been followed by many techniques. The results suggest that a Silicalite-like zeolite initially crystallizes quickly and thereafter the aluminum enters the structure probably through dissolution of the crystal aggregates and formation of real ZSM—5 zeolite.

Toluene disproportionation was performed at 300°–360°C in a fixed-bad reactor (carrier H 2 ) over samples of HZSM-5 differing in surface acidity, organic compound used for the synthesis, crystal size and procedure used for decationation. Xylene isomers in the product were in equilibrium ratios. The catalyst activity was found to be clearly dependent on surface acidity. An interpretation is given, in terms of a slow toluene disproportionation within the zeolite pores, followed by fast xylene isomerization on the external surface. Measurements of the reaction rate at 300°C over one of the catalysts confirmed a kinetic model as previously suggested.

The activity and selectivity to para -ethyltoluene in toluene alkylation with ethanol have been correlated to the structural and morphological features of the ZSM-5 and ZSM-11 zeolites employed as catalysts. In particular, as the particle size increases and correspondingly the surface area outside the zeolite channels decreases, lower activities and higher para -isomer selectivities (up to 90%) are obtained. This behavior has been interpreted by supposing a two-step mechanism: in the first step, para -isomer forms by toluene alkylation with high selectivity inside the zeolitic channels (shape selectivity), while in the second step the isomerization toward the thermodynamic equilibrium of the three isomers proceeds just on the external surface

Surface characterization of silicalite and titanium-silicalite is made by combined use of IR and UV-Vis reflectance spectroscopy. The nature of the IR modes and of the electronic transitions associated with framework titanium is discussed in detail. The perturbation caused by the adsorption of small polar molecules (H 2 O, NH 3 , CH 3 OH) on both the IR and UV-Vis spectra is discussed in terms of the formation of six-coordinated complexes by ligand insertion in the Ti(IV) coordination sphere. All the Ti(IV) is accessible to the interaction with the molecules.