La convergenza digitale. Lo scenario di riferimento, le soluzioni su cui puntare e la grande sfida: i contenuti e la loro destrutturazione

2007-10-30Sardegna Ricerche, Edificio 2, Località Piscinamanna 09010 Pula (CA) - ItaliaContenuti Digitali: una vera rivoluzione

Advances in Infrared Spectroscopy of Catalytic Solid-Liquid Interfaces: The Case of Selective Alcohol Oxidation

Progress in the use of ATR-IR spectroscopy to improve the understanding of liquid-phase heterogeneous catalytic reactions is illustrated using the example of the oxidation of benzyl alcohol over Pd/Al2O3 and Bi-Pd/Al2O3. The in situ studies performed in both batch and continuous reactor cells provide rich information on the reaction pathway and important facets of the mechanism, such as the nature of active Pd sites and the effect of the Bi-promoter. The combination of CO site blocking prior to reaction and isotopic labeling suggests that alcohol dehydrogenation occurs uniformly over Pd nanoparticles, but only selected sites may allow desorption of the product benzaldehyde thus providing the required selectivity. Promotion of Pd/Al2O3 using bismuth produces infrared spectra free of adsorbed CO. This information demonstrates that Bi is deposited on selected adsorption sites (terraces rather than defects) and simultaneously confirms that open terraces favor product decomposition. Experiments performed in the continuous reactor cell using different catalyst film thickness show that reactions can be studied under kinetic or mass transfer limited conditions depending on catalyst film thickness. This allowed to study the alcohol oxidation under conditions of oxygen diffusion limitation, which are preferably applied in praxis in order to prevent catalyst deactivation by over-oxidatio

Modulation Excitation X-Ray Absorption Spectroscopy to Probe Surface Species on Heterogeneous Catalysts

The advantages and open questions of the combination of modulation excitation spectroscopy and phase sensitive detection (PSD) with X-ray absorption spectroscopy (XAS) for the analysis of heterogeneous catalysts at work are reviewed. The characteristic spectral signatures of two different edges (Pd K and Pt L3) are described in relation to the red-ox chemistry of Pd/Al2O3 and Pt/Al2O3 with respect to NO reduction by CO and CO oxidation, respectively. Both examples demonstrate that PSD makes XAS sensitive to potentially active species for the catalytic reactio

Structural Reversibility of LaCo1-xCuxO3 Followed by In Situ X-ray Diffraction and Absorption Spectroscopy

Combinations of perovskite-type oxides with transition andprecious metals exhibit a remarkable self-regenerable propertythat could be exploited for numerous practical applications. Theobjective of the present work was to study the reversibility ofstructural changes of perovskite-type oxides under cyclicreducing/oxidizing atmosphere by taking advantage of thereducibility of LaCoO3. LaCoO3 dand LaCo0.8Cu0.2O3 dwereprepared by ultrasonic spray combustion and were character-ized by scanning electron microscopy (SEM), X-ray diffraction(XRD), X-ray absorption spectroscopy (XAS) and temperature-programmed reduction (TPR). XRD and XAS data confirmed thatcopper adopted the coordination environment of cobalt at theB-site of the rhombohedral LaCoO3under the selected synthesisconditions. The structural evolution under reducing atmospherewas studied byin situXRD and XANES supporting the assign-ment of the observed structural changes to the reduction of theperovskite-type oxide from ABB’O3(B’=Cu) to B’0/ABO3and toB’0B0/A2O3. Successive redox cycles allowed the observation of anearly complete reversibility of the perovskite phase, i.e. copperwas able to revert into LaCoO3upon oxidation. The reversiblereduction/segregation of copper and incorporation at the B-siteof the perovskite-type oxides could be used in chemicalprocesses where the material can be functionalized bysegregation of Cu and protected against irreversible structuralchanges upon re-oxidation.Ministerio de Investigación de España (MINECO)-CTQ2014-60524-RUniversidad de Sevilla-IV PPIT-U

Energy conversion processes with perovskite-type materials

Mixed oxides derived from the perovskite structure by combination of A- and B-site elements and by partial substitution of oxygen provide an immense playground of physico-chemical properties. Here, we account for own research conducted at the Paul Scherrer Institute on perovskite-type oxides and oxynitrides used in electrochemical, photo(electro)chemical and catalytic processes aiming at facing energy relevant issues

Preferential oxidation of CO on a La-Co-Ru perovskite-type oxide catalyst

A Ru-containing perovskite-type oxide La(Co,Ru)O3 of nominal composition LaCo0.8Ru0.2O3 was prepared by ultrasonic spray combustion and tested for the preferential oxidation of CO (PROX). EXAFS indicated that Ru adopted the coordination environment of Co in LaCoO3 while Co was present as LaCoO3 and Co3O4. PROX activity was replaced by CO hydrogenation activity above 250 °C. Short oxidation at 500 °C between temperature programmed reaction ramps did not restore the initial La(Co,Ru)O3 structure but generated a catalyst with improved PROX activity compared to the initial La(Co,Ru)O3. Under reductive PROX conditions the material experienced structural changes that improved its overall catalytic activity only if the catalyst was oxidized after each temperature programmed ramp.Spanish Ministry of Research (Project CTQ2014-60524-R)University of Seville for a scholarship for R.P. and the Swiss National Science Foundation (SNF)(Project nr. 200021_159568

PdO x /Pd at Work in a Model Three-Way Catalyst for Methane Abatement Monitored by Operando XANES

The oxidation state of palladium in a model Pd/ACZ three-way catalyst was monitored by synchronous XANES and mass spectrometry during two consecutive heating (to 850°C) and cooling (to 100°C) cycles under stoichiometric conditions simulating exhaust after treatment of a natural gas engine. During heating in the first cycle, PdO reduction occurred around 500°C and the initial fully oxidized state of Pd was never recovered upon heating and cooling cycles. A mixed Pd2+/Pd oxidation state was at work in the second cycle. Hence, the operando XANES study reveals that the PdO x /Pd pair exists in a working catalyst but is less active than the catalyst in its initial state of fully oxidized palladium. It is also evident from XANES spectra that ceria-zirconia promotes re-oxidation of metallic Pd, thus reasonably sustaining catalytic activity after exposure to high temperature