Publications (14)23.58 Total impact
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Article: Electron paramagnetic resonance analysis of La(1-x)M(x)MnO(3+δ) (M = Ce, Sr) perovskite-like nanostructured catalysts.
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ABSTRACT: The physical-chemical properties of some nanostructured perovskite-like catalysts of general formula La(1-x)M(x)MnO(3+δ) (M = Ce, Sr) have been investigated, in particular by using the electron paramagnetic resonance (EPR) technique. We show that the interplay between the -O-Mn(3+)-O-Mn(4+)-O- electron double-exchange and the electron mobility is strictly dependent on the dopant nature and the annealing conditions in air. A relationship between the observed properties of these samples and their activity in the methane flameless catalytic combustion is proposed.Inorganic Chemistry 07/2012; 51(15):8433-40. · 4.60 Impact Factor -
Article: Spectroscopic Enlightening of the Local Structure Of VOX Active Sites in Catalysts for the Odh of Propane
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ABSTRACT: Site isolation of V active sites has been often correlated to catalytic performance for the oxidative dehydrogenation (ODH) of propane to propylene. In particular, catalyst selectivity seems favored by high V dispersion. The latter property is hardly attainable by traditional preparation methods, especially by impregnation except at very low V loading, which however may lead to a too high surface exposure of the acidic sites of the support. In this paper, the effect of the preparation procedure on catalyst properties has been investigated, particularly considering catalysts prepared by flame pyrolysis, a synthesis method which induced a very high V dispersion also at relatively high vanadium loading. Transmission electron microscopy also allowed us to assess V oxide dispersion depending on both the support type and the preparation method. Furthermore, the local structure of the V active sites has been deeply investigated by X-ray absorption spectroscopy, allowing us to propose a possible structure of the active sites. The average oxidation state of surface V species was then studied by X-ray photoelectron spectroscopy (XPS), showing a role of V oxidation state on catalyst selectivity. The catalytic performance has been interpreted on the basis of V species and catalyst acidity (as measured by IR spectroscopy), another fundamental parameter that in turn results to be correlated with V dispersion on different supports. More selective catalysts were indeed characterized by the presence of weaker Brønsted acidic sites.The Journal of Physical Chemistry C 01/2012; 116(42):22386. · 4.80 Impact Factor -
Article: EXAFS-XANES evidence of in situ cesium reduction in Cs-Ru/C catalysts for ammonia synthesis.
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ABSTRACT: We present here a X-ray absorption spectroscopy (XAS) investigation on the local chemical order and electronic structure of Cs and Ba, promoters of the Ru/C catalysts for ammonia synthesis that attracted interest because of highly increased productivity. The role of the promoters is still largely unclear, although indirect evidence for Cs partial reduction has been obtained by this and other groups. Our XAS analysis with in situ H(2) reduction directly supports the partial Cs reduction in the promoted Ru/C catalysts, depending on the presence of Ru and on the graphitization degree of the support. Higher coordination of Ba was observed with respect to Cs in the reduced samples, without evidence of heavy atoms (Ru, Cs, and Ba) in the surroundings. Because of the strong electropositive nature of Cs, direct experimental evidence of its partial reduction is of outstanding significance also for other applications.Inorganic Chemistry 03/2011; 50(8):3757-65. · 4.60 Impact Factor -
Article: A photocatalytic water splitting device for separate hydrogen and oxygen evolution.
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ABSTRACT: A two-compartment Plexiglas cell has been set up and tested for separate hydrogen and oxygen production from photocatalytic water splitting on a thin TiO2 layer deposited by magnetron sputtering on a flat Ti electrode inserted between the two cell compartments.Chemical Communications 01/2008; · 6.17 Impact Factor -
Chapter: Oxide Nanomaterials for the Catalytic Combustion of Hydrocarbons
07/2006: pages 563 - 601; , ISBN: 9780470108970 -
Article: Kinetic Study of Ammonia Synthesis on a Promoted Ru/C Catalyst
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ABSTRACT: A set of kinetic tests on a promoted Ru/C catalyst for ammonia synthesis has been carried out under industrially relevant reaction conditions (T = 370−460 °C, P = 50−100 bar). The results have been elaborated by using some kinetic models either derived from literature or here-developed. The best results, as for fitting and consistency of the optimized parameters, were obtained by simply modifying the Temkin equation with the addition of H2 and NH3 adsorption terms, to take into account their inhibiting effect on catalyst performance. Such an equation can be advantageously applied for better design and operation of ammonia synthesis reactors using Ru/C catalysts. The activation energy for the synthesis reaction was 23 kcal/mol, much lower than that previously found for Fe-based catalysts. From a practical point of view, it has been shown that the working pressure can be decreased, with the same plant productivity, by 40−50% when using the present Ru/C catalyst. Likewise, the ammonia concentration in the exit gas can be increased by about the same value if the working pressure is not decreased.05/2006; -
Article: Promoters effect in Ru/C ammonia synthesis catalyst
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ABSTRACT: A series of carbon-supported, ruthenium-based catalysts, variously promoted with alkali and alkali-earth compounds, were prepared, aiming at investigating the effect of such promoters on catalyst activity and stability. It was found that a simultaneous action of three promoters (K + Ba + Cs) maximised both activity and thermal resistance of the catalyst. In particular, Ba is very effective in providing catalyst activity and resistance to methanation, while Cs strongly improves resistance to metal sintering. A further activity improvement is given by K as third promoter. Through a XPS study, the promoter effect was confirmed to be essentially of electronic nature. The optimal catalyst composition, in terms of activity, thermal resistance in the reaction environment and cost, corresponds to Ru ca. 5 wt.%, Ba/Ru = 0.6, Cs/Ru = 1 and K/Ru = 3.5 atomic ratios.Applied Catalysis A: General. 01/2001; 208:271-278. -
Article: Preparation by flame spray pyrolysis of ABO3±δ catalysts for the flameless combustion of methane
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ABSTRACT: Perovskitic mixed oxides prepared through flame-spray pyrolysis possess a good stability in high-temperature application, viz. the catalytic flameless combustion of methane. Some preparation operating parameters are here analysed, such as O2 pressure drop along the spraying nozzle, O2 discharge velocity and flow rate. These parameters have been correlated with specific surface area, activity and durability of the prepared samples, as well as with flame temperature, varied by using different fuel mixtures. It was found that specific surface area increases with increasing O2 velocity and flow rate and with decreasing the combustion enthalpy of the solvent mixture. This reflects on both activity and durability of the catalyst.Catalysis Today 117(4):549-553. · 3.41 Impact Factor -
Article: Carbon-supported promoted Ru catalyst for ammonia synthesis
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ABSTRACT: A series of alkali- and/or alkali-earth-promoted, carbon-supported Ru catalysts have been prepared by impregnation from aqueous solutions of the precursors. The supports have been pretreated by heating in inert atmosphere at various temperatures, followed by partial oxidation in air at 425°C and then by hydrogen treatment at 900°C. The catalyst samples, diluted 1/22 with quartz powder, have been studied in ammonia synthesis by means of a bench-scale, downflow, continuous, tubular reactor, under standard reaction conditions (430°C, 100 bar total pressure, H2/N2 = 1.5/1 feeding ratio). Caesium and Barium proved to be much more effective promoters than Potassium as promoters and the optimal temperature range for support pretreatment was found to be about 1900°C. The ammonia productivity, on a catalyst volume basis, of our best Ru catalyst was about twice higher than that of the most widely used Fe-based commercial catalysts.Applied Catalysis A: General. 185(2):269-275. -
Article: Catalytic flameless combustion of methane over perovskites prepared by flame–hydrolysis
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ABSTRACT: A set of perovskite-type catalysts of general formula LaBO3±δ (B=Co, Mn, Fe) and a sample of La2NiO4±δ were prepared by means of a recently proposed innovative flame–hydrolysis procedure. The catalysts were characterised by nanometer-size particles (20–60 nm), relatively high surface area (ca. 20 m2/g), high thermal stability and high phase purity. Their high activity for the catalytic flameless combustion of methane confirmed the validity and versatility of the preparation method.Temperature-programmed -desorption and -reaction, coupled with mass spectrometric analysis, allowed to better understand some aspects of the catalytic behaviour shown by the present samples for the cited reaction. In particular, an interesting correlation between the availability of oxygen at various temperatures, as revealed by the so-called α and β oxygen desorption peaks, and reaction mechanism was found for the different B metals.Applied Catalysis B: Environmental. -
Article: Effect of surface acidity on the behaviour of Fe-MFI catalysts for benzene hydroxylation to phenol
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ABSTRACT: FTIR and microcalorimetric analysis of adsorbed pyridine has been employed for the characterisation of a set of Fe-MFI zeolite catalysts with different Si/Al and Si/Fe ratios, used for the gas phase hydroxylation of benzene to phenol by N2O. Catalysts behaviour in terms of activity and deactivaton rate is discussed in relation to the nature, concentration and strength of their surface acid sites. Surface acidity, though not involved directly in the hydroxylation reaction, plays a major role in determining catalyst lifetime. Coke formation, leading to catalyst deactivation, is triggered by further undesired reactions of phenol and is favoured by the strong adsorption of the latter on Lewis acid sites, restraining its diffusion out of the zeolite pores.Applied Catalysis A: General. -
Article: Graphitised carbon as support for Ru/C ammonia synthesis catalyst
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ABSTRACT: In the present work, we compared the catalytic activity and mainly the stability under the usual ammonia synthesis conditions, of some carbon supports, differing as for their nature, purity and temperature of pretreatment. The effect of catalyst composition (metal and promoters loading) on stability was also investigated. XRD and N2 adsorption/desorption analysis helped in elucidating the effect of carbon treatment. It was found that only after the support has been heated at least at 1900 °C the stability of the tri-promoted catalyst becomes fully satisfactory and virtually independent of Ru loading. For practical purposes such high temperature treatment must be compatible with the preservation of a sufficiently high surface area.Catalysis Today. -
Article: Flame-spray pyrolysis preparation of perovskites for methane catalytic combustion
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ABSTRACT: A flame spray pyrolysis apparatus was set up and optimised for the preparation of perovskitic mixed-metal oxides in nanoparticle-size powder form. LaCoO3 was chosen as test catalyst, aiming at correlating crystallinity, surface area, particle size, catalytic activity, and durability with some fundamental operating parameters of the apparatus. In particular, the feeding rate of the precursor solution, the flow rate of the O2/CH4 mixture for the igniter, and flow rate and linear velocity of the main dispersing-oxidising oxygen were thoroughly analysed. The activity of the prepared samples was tested for the catalytic flameless combustion of methane, a reaction requiring the proper combination of catalyst activity and thermal stability. Provided that a crystalline perovskitic phase forms, activity increases with increasing surface area of the powder. In contrast, the higher the initial sintering of catalyst particles within the flame, the higher is thermal stability. Tuning up the operating parameters allows us to properly address the desired catalyst properties.Journal of Catalysis. -
Article: Characterisation of Ru/C catalysts for ammonia synthesis by oxygen chemisorption
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ABSTRACT: A standard chemisorption procedure has been set up for the determination of Ru dispersion in Ru/C catalysts. Pulse chemisorption of oxygen was carried out at 0 °C, after having proved that no corrosive chemisorption phenomena are present. An average chemisorption stoichiometry was experimentally determined through measurements on Ru black. The procedure was applied to the investigation of promoted and unpromoted Ru/C catalysts for ammonia synthesis, supported on two different carbon supports. The main factor influencing Ru dispersion showed to be Ru loading, while the addition of even large amounts of Ba–Cs–K promoters has practically no influence. It is also briefly discussed how such results can help in elucidating several aspects of the behaviour of Ru/C as catalyst for ammonia synthesis.Applied Catalysis A: General.
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Institutions
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2001–2012
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University of Milan
- • Department of Chemistry, Biochemistry and Biotechnologies for Medical Sciences
- • Department of Physical Chemistry and Electrochemistry
Milano, Lombardy, Italy
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