Chimet SpA

Arezzo, Italy

Chimet SpA

Arezzo, Italy
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Bugaev A.L.,University of Turin | Guda A.A.,Southern Federal University | Lomachenko K.A.,European Synchrotron Radiation Facility | Shapovalov V.V.,Southern Federal University | And 10 more authors.
Journal of Physical Chemistry C | Year: 2017

We report an in situ, temperature and H2 pressure-dependent, characterization of (2.6 ± 0.4) nm palladium nanoparticles supported on active carbon during the process of hydride phase formation. For the first time the core-shell structure is highlighted in the single-component particles on the basis of a different atomic structure and electronic configurations in the inner "core" and surface "shell" regions. The atomic structure of these particles is examined by combined X-ray powder diffraction (XRPD), which is sensitive to the crystalline core region of the nanoparticles, and by first shell analysis of extended X-ray absorption fine structure (EXAFS) spectra, which reflects the averaged structure of both the core and the more disordered shell. In the whole temperature range (0-85 °C), XRPD analysis confirms the existence of two well-separated α- and β-hydride phases with the characteristic flat plateau in the phase transition region of the pressure-lattice parameter isotherms. In contrast, first shell interatomic distances obtained from EXAFS exhibit a slope in the phase transition region, typical for nanostructured palladium. Such difference is explained by distinct properties of bulk "core" which has crystalline structure and sharp phase transition, and surface "shell" which is amorphous and absorbs hydrogen gradually without forming distinguishable α- and β-phases. Combining EXAFS and XRPD we extract, for the first time, the Pd-Pd first-shell distance in the amorphous shell of the nanoparticles, that is significantly shorter than in the bulk core and relevant in catalysis. The core/shell model is supported by the EXAFS analysis of the higher shells, in the frame of the multiple scattering theory, showing that the evolution of the third shell distance (ΔR3/R3) is comparable to the evolution of (Δa/a) obtained from XRPD since amorphous PdHx shell gives a negligible contribution in this range of distances. This operando structural information is relevant for the understanding of structure-sensitive reactions. Additionally, we demonstrate the differences in the evolution of the thermal parameters obtained from EXAFS and XRPD along the hydride phase formation. © 2017 American Chemical Society.

Agostini G.,University of Turin | Agostini G.,European Synchrotron Radiation Facility | Piovano A.,Laue Langevin Institute | Bertinetti L.,Max Planck Institute of Colloids and Interfaces | And 4 more authors.
Journal of Physical Chemistry C | Year: 2014

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 distributions is compatible with given values of ACN and AD. In this way, we have established a general method to properly take into account the above-mentioned parameters and to allow for an accurate analysis and comparison of results. Furthermore, it will be shown that unfavorable distribution shape makes the comparison among techniques critical and potentially misleading if performed with an oversimplified model of the PSD such as those using the average diameter only. © 2014 American Chemical Society.

Pellegrini R.,Chimet SpA | Agostini G.,University of Turin | Groppo E.,University of Turin | Piovano A.,University of Turin | And 2 more authors.
Journal of Catalysis | Year: 2011

A systematic study on several spent catalysts, withdrawn from different terephthalic acid purification reactors loaded with the same fresh catalyst (0.5 wt.% Pd/C, type D3065, supplied by Chimet SpA), has been carried out. Spent catalysts characterized by different lifetimes, position in the catalytic bed, sintering degree, and types of contaminant (mainly S, Pb, and Mo) have been investigated by TEM coupled with EDS detection, XRPD, EXAFS spectroscopy, and CO chemisorption. The Pd sintering process involves all catalysts, irrespective of the nature and amount of contaminants that have no influence on sintering rate except for S poisoning. Pd sintering occurs following different steps, leading to the formation of larger crystals, aggregates, and agglomerates, the last being the primary cause of the loss of Pd surface area and, consequently, of the decrease in catalytic activity. Among the investigated contaminants, S and Pb are the worst, because they strongly interact with Pd, forming from surface adlayers (not detectable by XRPD, but visible by EDS mapping) up to bulk Pd 4S or Pd3Pb alloys (easily detectable by XRPD). In both cases, the catalytic activity decreases. In contrast, Mo, Cr, Fe, Ti, and Al do not interact preferentially with Pd (no alloys have been detected, although the contaminants are present in relevant concentrations): They have been found to be spread on the whole catalyst surface. Accordingly, no direct effect of these contaminants on catalytic activity loss has been evidenced. © 2011 Elsevier Inc. All rights reserved.

Preti D.,University of Pisa | Resta C.,University of Pisa | Squarcialupi S.,Chimet SpA | Fachinetti G.,University of Pisa
Angewandte Chemie - International Edition | Year: 2011

AUROlite, consisting of gold supported on titania (picture shows extrudates in a steel net cage), is a robust catalyst for the production of catalyst-free HCOOH/NEt 3 adducts from H 2, CO 2, and neat NEt 3. Pure HCOOH is freed from the adducts by amine exchange. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preti D.,University of Pisa | Squarcialupi S.,Chimet SpA | Fachinetti G.,University of Pisa
Angewandte Chemie - International Edition | Year: 2010

"Chemical Equaction Presented" Adding HCOOH to NEt3 gives a biphasic system of amine and an adduct with a molar acid/amine ratio (AAR) of 1.33. In the presence of a suitable catalyst, CO2/H 2 (1:1) acts as HCOOH if both amine and 1.33-adduct phases are present. For example, at 4O°C and 120 bar, neat amine, "doped" with both 1.33 adduct and catalyst, is quantitatively converted into 1.78 adduct, which is distilled as an azeotrope with AAR = 2.35. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

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