Gloria Berlier

Determination of the oxidation and coordination state of copper on different Cu-based catalysts by XANES spectroscopy in situ or in operando conditions

The use of XANES spectroscopy, both in classical and in dispersive geometries, is illustrated for the study of copper-based catalysts under in situ or in operando conditions. As case studies, copper-exchanged MFI zeolites and CuCl2/γ-Al2O3 systems are considered. In the former case, in situ XANES spectroscopy was used to characterise well defined complexes (Cu+N2, Cu+(CO)3, Cu+(NH3)(CO) and Cu+(NO)2) formed on copper ions inside the zeolite cavities under controlled conditions. From these results, useful information concerning the symmetry of the formed complexes can readily be gained. The latter case shows how the use of dispersive XANES spectroscopy allows to follow, in real time, the evolution of a system in working conditions. The simultaneous determination of the catalyst activity and of the average oxidation state of copper in the catalyst allows the evolution of a system in working conditions to be followed in real time. The criteria used for the quantification of the Cu(I) and Cu(II) fraction from XANES spectra are discussed in detail.

An in situ temperature dependent IR, EPR and high resolution XANES study on the NO/Cu+–ZSM-5 interaction

We report an in situ IR, EPR, and high resolution XANES study on the Cu+(NO) and Cu+(NO)2 complexes formed at 80 K in Cu+–ZSM-5. Bare Cu2+ ions (<1%) exhibit an axial EPR spectrum, while bare Cu+ ions exhibit well resolved 1s→4pxy and 1s→4pz transitions (pxy/pz splitting of 3.1 eV), reflecting the same local symmetry. Cu+(NO) complex exhibits an anisotropic EPR signal, while XANES spectrum of dinitrosyl adducts presents three resolved components ascribed to the 1s→4px, 1s→4py, and 1s→4pz transitions (px/py and py/pz splitting of 3.8 and 2.6 eV, respectively) testifying the rupture of the axial symmetry of Cu+ bare cations upon NO adsorption. Upon increasing the temperature to 300 K, NO oxidizes a fraction of 75–85% of the cuprous ions.

The role of Al in the structure and reactivity of iron centers in Fe-ZSM-5-based catalysts: a statistically based infrared study

Abstract A statistical analysis of the infrared data obtained upon absorption of NO on a large number of Al-free Fe-silicalite and Fe-ZSM-5 samples highlighted the influence of Al on the formation and stabilization of extraframework iron species and shed more light on the superior activity of Fe-ZSM-5-based catalysts. It was concluded that Al favors the dispersion of extraframework iron species and that isolated Fe II species with one or two Al atoms in the immediate vicinity are the active sites in partial oxidation reactions. The structure of the α -oxygen species adsorbed on iron centers is also briefly discussed.

Interaction of N2, CO and NO with Cu-exchanged ETS-10: a compared FTIR study with other Cu-zeolites and with dispersed Cu2O ☆

Abstract After a brief overview of the reasons why, in spite of the high fraction of framework Ti(IV) atoms, Engelhard titanosilicate (ETS-10) cannot be used as competitive catalyst in partial oxidation reactions, we draw the attention on the fact that the high cation density of ETS-10 can be the key property for potential new catalytic applications of this recent material. Among all, cation exchange with Cu2+ can yield to Cu-ETS-10, a promising material for environmental catalysis. We so present a detailed characterization of this material using N2, CO and NO as probe molecules. In spite of the rather high complexity of the obtained spectra, a comparison with similar experiments (described in the literature or ad hoc performed for this work) on other Cu-exchanged zeolites and on Cu2O dispersed on silica and on MCM-41, allows a full interpretation of the spectroscopic properties. It is shown that copper is present both as counterion and in the form of Cu2O nanoclusters dispersed in the ETS-10 channels and in the external surface. Finally, IR spectroscopy has been used to demonstrate that Cu-ETS-10 is active in the decomposition of NO.

Activity and deactivation of Fe-MFI catalysts for benzene hydroxylation to phenol by N2O

Abstract Isomorphously substituted Fe-MFI zeolite catalysts with various Si/Al and/or Si/Fe ratios were synthesized and characterized by many different techniques, such as ICP, XRD, SEM, TPR, microcalorimetry, FTIR, and EPR. Under standard reaction conditions the best catalyst gave 20% benzene conversion and over 90% selectivity to phenol. For Fe-ZSM5 catalysts, addition of steam to the feed improved catalyst activity, selectivity, and durability. Phenol formed onto Fe-based sites only. Active sites could very likely be composed of oxygen-bridged, extraframework binuclear Fe redox species, charge-compensating the framework Fe 3+ or Al 3+ ions. Surface acidity was not responsible for activity in the main reaction, but it was heavily involved in catalyst deactivation by coking. Catalyst deactivation derived mainly from the decomposition-condensation of phenol onto acid sites; the stronger the latter, the quicker was the coking rate.

The Cu-CHA deNOx Catalyst in Action: Temperature-Dependent NH3-Assisted Selective Catalytic Reduction Monitored by Operando XAS and XES

The small-pore Cu-CHA zeolite is today the object of intensive research efforts to rationalize its outstanding performance in the NH3-assisted selective catalytic reduction (SCR) of harmful nitrogen oxides and to unveil the SCR mechanism. Herein we exploit operando X-ray spectroscopies to monitor the Cu-CHA catalyst in action during NH3-SCR in the 150-400 °C range, targeting Cu oxidation state, mobility, and preferential N or O ligation as a function of reaction temperature. By combining operando XANES, EXAFS, and vtc-XES, we unambiguously identify two distinct regimes for the atomic-scale behavior of Cu active-sites. Low-temperature SCR, up to ∼200 °C, is characterized by balanced populations of Cu(I)/Cu(II) sites and dominated by mobile NH3-solvated Cu-species. From 250 °C upward, in correspondence to the steep increase in catalytic activity, the largely dominant Cu-species are framework-coordinated Cu(II) sites, likely representing the active sites for high-temperature SCR.

Mesoporous silica as topical nanocarriers for quercetin: characterization and in vitro studies.

The flavonoid quercetin is extensively studied for its antioxidant and chemopreventive properties. However the poor water-solubility, low stability and short half-life could restrict its use in skin care products and therapy. The present study was aimed to evaluate the potential of aminopropyl functionalized mesoporous silica nanoparticles (NH2-MSN) as topical carrier system for quercetin delivery. Thermo gravimetric analysis, X-ray diffraction, high resolution transmission electron microscopy, nitrogen adsorption isotherms, FT-IR spectroscopy, zeta potential measurements and differential scanning calorimetry allowed analyzing with great detail the organic-inorganic molecular interaction. The protective effect of this vehicle on UV-induced degradation of the flavonoid was investigated revealing a certain positive influence of the inclusion on the photostability over time. Epidermal accumulation and transdermal permeation of this molecule were ex vivo evaluated using porcine skin mounted on Franz diffusion cells. The inclusion complexation with the inorganic nanoparticles increased the penetration of quercetin into the skin after 24h post-application without transdermal delivery. The effect of quercetin alone or given as complex with NH2-MSN on proliferation of JR8 human melanoma cells was evaluated by sulforhodamine B colorimetric proliferation assay. At a concentration 60 μM the complex with NH2-MSN was more effective than quercetin alone, causing about 50% inhibition of cell proliferation.

Stabilization of quercetin flavonoid in MCM-41 mesoporous silica: positive effect of surface functionalization

Antioxidants can prevent UV-induced skin damage mainly by neutralizing free radicals. For this purpose, quercetin (Q) is one of the most employed flavonoids even if the potential usefulness is limited by its unfavorable physicochemical properties. In this context, mesoporous silica (MCM-41) is herein proposed as a novel vehicle able to improve the stability and performance of this phenolic substrate in topical products. Complexes of Q with plain or octyl-functionalized MCM-41 were successfully prepared with different weight ratios by a kneading method, and then, they were characterized by XRD, gas-volumetric (BET), TGA, DSC, and FTIR analyses. The performances of the different complexes were evaluated in vitro in terms of membrane diffusion profiles, storage and photostability, antiradical and chelating activities. The physicochemical characterization confirmed an important host/guest interaction due to the formation of Si-OH/quercetin hydrogen-bonded adducts further strengthened by octyl functionalization through van der Waals forces. The immobilization of Q, particularly on octyl-functionalized silica, increased the stability without undermining the antioxidant efficacy opening the way for an innovative employment of mesoporous composite materials in the skincare field.

FTIR and UV–Vis characterization of Fe-Silicalite

Abstract FTIR and diffuse reflectance UV–Vis spectroscopies were used to investigate the nature of the extra-framework iron species in Fe-Silicalite using NO as probe molecule. After removal of the template at 773 K, ferrous species present in two different coordinative states, namely Fe A 2+ and Fe B 2+ , were mainly detected. The Fe A 2+ species are highly coordinatively unsaturated and can form a [Fe A (NO) n ] 2+ (with n >2) polynitrosyl complex characterized by IR bands at 1914, 1880–1850, and 1808 cm −1 and by an electronic transition at 23,000 cm −1 . Upon reducing the NO pressure, this complex is transformed into a [Fe A (NO) 2 ] 2+ dinitrosyl characterized by a doublet of IR bands at 1839 and 1765 cm −1 . Fe B 2+ is less coordinatively unsaturated and forms only [Fe B (NO)] 2+ mononitrosyl (absorbing in the IR at 1839 cm −1 and at 26,500 and 17,500 cm −1 in the UV–Vis). Upon dosage of H 2 O, the Fe B 2+ species becomes able to uptake further NO ligands to give new polynitrosyl species spectroscopically indistinguishable from those formed on the Fe A 2+ species. Based on these results, some hypotheses about the structure of Fe A 2+ and Fe B 2+ are advanced.

Description of a flexible cell for in situ X-ray and far-IR characterization of the surface of powdered materials

Abstract We have designed and realized a cell where a powdered sample, in form of self-supported pellet, can be (i) in situ heated up to 900 K, either under dynamical vacuum or in reducing/oxidizing atmosphere; (ii) contacted with the desired amount of adsorbed gas; (iii) cooled down to 77 K for measurements. The cell (transmission geometry) has been employed in X-ray absorption experiments at LURE DCI (EXAFS13) and ESRF (GILDA BM8 and ID24), in far-IR experiments at LURE Super-ACO (SIRLOIN) and in conventional mid-IR experiments in our laboratory, only by changing the windows (mylar, silicon and KBr, respectively). A brief overview on the results obtained with this cell is reported to illustrate the potentialities of the instrument. Literature is quoted to allow possible in-depth study.