Ilenia Rossetti

Perovskite catalysts for the catalytic flameless combustion of methane: Preparation by flame-hydrolysis and characterisation by TPD–TPR-MS and EPR

Abstract A new method was employed for the preparation of a set of lanthanum cobaltites of general formula La1−xMxCoO3+δ with M=Ce, Eu and x=0, 0.05, 0.1, 0.2. All the samples thus prepared were nanostructured, thermally very stable and characterised by highly crystalline perovskite-like structure and high surface area. Their activity as catalysts for the catalytic flameless combustion (CFC) of methane was by ca. one order of magnitude higher than that of their analogues, prepared through the usual calcination-milling (CM) procedure. Adsorption of oxygen was accompanied by formation of paramagnetic species. Desorption of preadsorbed oxygen was dependent on the nature of the doping element and on the value of the stoichiometric coefficient x of their formula. A correlation between the temperature of the maximal rate of oxygen release and catalytic activity was found. The following scale of activity for the title reaction versus x values could be set up: 0.1Ce>0.05Ce>0>0.05Eu>0.1 Eu≅0.2Ce. The higher activity of Ce-doped catalysts as compared to those doped with Eu was found to be related to the strength of the bond between oxygen and Co ions.

Catalytic combustion of hydrocarbons over perovskites

Abstract The advantages and disadvantages of the catalysts so far employed or proposed for the low temperature catalytic combustion of hydrocarbons, in both static and mobile energy production devices, are discussed. Furthermore, a La0.9Ce0.1CoO3±δ perovskite has been prepared by a recently proposed new flame-hydrolysis (FH) method. This proved a high surface area, thermally highly resistant catalyst. The partial substitution of Ce for La in such a cobaltite led to a relatively low suprafacial activity, but to a high bulk oxygen mobility, leading to high intrafacial activity for the catalytic flameless combustion of methane. The best operating conditions have been also found, for supporting the so prepared active phase, by dip-coating of a cordieritic honeycomb support, after deposition of an alumina primer. A very active and durable catalyst was so obtained, useful for practical application in the environmentally friendly low temperature combustion of methane.

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.

Nickel Catalysts Supported Over TiO2, SiO2 and ZrO2 for the Steam Reforming of Glycerol

Ni‐based catalysts supported on TiO2, ZrO2 and SiO2 (in the form of mesoporous Santa Barbara Amorphous 15 (SBA‐15) and amorphous dense nanoparticles), were employed in the steam reforming of glycerol. Each sample was prepared by liquid phase synthesis of the support followed by impregnation with the active phase and calcination at 800 °C or by direct synthesis through flame pyrolysis. Many techniques have been used to assess the physical chemical properties of both the fresh and spent catalysts, such as atomic absorption, N2 adsorption/desorption, XRD, SEM, TEM, temperature‐programmed reduction (TPR), X‐ray photoelectron spectroscopy (XPS), Micro‐Raman and FTIR spectroscopy. The samples showed different textural, structural and morphological properties, as well as different reducibility and thermal resistance depending on the preparation method and support. Some of these properties were tightly bound to catalyst performance, in terms of H2 productivity and stability towards coking and sintering. A key parameter was the metal–support interaction, which strongly depended on the preparation procedure. In particular, the stronger the interaction, the more stable the metallic Ni clusters, which in turn lead to a higher catalytic activity and stability. Surface acidity was also taken into account, in which the nature of the acid sites was differentiated (silanols, titanols or Lewis acid sites). The characterisation of the spent catalysts also allowed us to interpret the deactivation process. The formation of multi‐walled nanotubes was observed for every sample, though it was only in some cases that this led to severe deactivation.

Effect of primer on honeycomb-supported La0.9Ce0.1CoO3±δ perovskite for methane catalytic flameless combustion

Abstract A set of La0.9Ce0.1CoO3 combustion catalysts, supported onto commercial cordierite monoliths, through either La2O3 or Al2O3 as primer, was prepared with different active phase/primer combinations. Two different salts were tested as precursors of the La-based primer. The behaviour of the catalysts for the methane flameless combustion was compared with that of samples prepared in the absence of any primer. The primers and the active phase were deposited by means of the dip-coating technique. The preparation conditions of the suspension and/or solution for the dip coating were studied, aiming at obtaining a uniform and resistant deposition. The catalysts were characterised, before and after the activity tests, by BET, X-ray diffraction analysis (XRD) and scanning electron microscope (SEM). The comparison between the catalysts showed that with Al2O3 as primer the catalyst possesses a higher surface area (SA) and hence a higher initial activity, while with La2O3 as primer a very high thermal stability can be obtained.

A photocatalytic water splitting device for separate hydrogen and oxygen evolution.

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.

Benzyl Alcohol Oxidation on Carbon‐Supported Pd Nanoparticles: Elucidating the Reaction Mechanism

Experiments were conducted on the liquid‐phase oxidation of benzyl alcohol over Pd nanoparticles, with the aim of determining the operative chemical reaction. Experiments were conducted in a batch reactor with para‐xylene as the solvent and continuous gas purging of the headspace. The following experimental parameters were varied: the initial benzyl alcohol concentration, the oxygen partial pressure in the headspace, and the reactor temperature. From trends in the concentration profiles and integrated production of each product, it was determined that there are two primary reaction paths: A) an alkoxy pathway leading to toluene, benzaldehyde, and benzyl ether, and B) a carbonyloxyl pathway (“neutral carboxylate”) leading to benzoic acid, benzene, and benzyl benzoate. From the mechanism elucidated, it is clear that the coverages of atomic hydrogen, atomic oxygen, and surface hydroxyls must be accounted for to achieve a complete description of the quantitative kinetics.

Hydrogen Production by Photoreforming of Renewable Substrates

This paper focuses on the application of photocatalysis to hydrogen production from organic substrates. This process, usually called photoreforming, makes use of semiconductors to promote redox reactions, namely, the oxidation of organic molecules and the reduction of H

Wustite as a new precursor of industrial ammonia synthesis catalysts

Contradictory results about the best oxidic precursor of Fe ammonia synthesis catalyst prompted the present comparative investigation on wustite- and magnetite-based catalysts. Many physical (density, porous texture, crystalline phases, reduction rate, metal surface, abrasion loss) and catalytic (kinetic constants, thermoresistancy) properties have been determined on both catalysts. The wustite-based catalyst proved to be much more active, especially at lower temperatures, approaching the performances of Ru/C catalyst, except at high conversion. Possible reasons for such a behavior of the wustite-based catalyst are discussed, suggesting that a reconsideration of the present consolidated knowledge on Fe ammonia synthesis catalyst might be convenient.

Study of Fe-silicalite catalyst for the N2O oxidation of benzene to phenol

Abstract A set of Fe-silicalite samples of MFI structure have been prepared by the hydrothermal technique, followed by steaming and by further chemical treating of the solid. After characterisation by nitrogen adsorption/desorption, X-ray diffraction (XRD), scanning electron microscopy-electron probe micro analysis (SEM-EPMA), the samples have been tested as catalysts for the oxidation of benzene to phenol by N 2 O. The best performing catalyst has been studied also by temperature programmed desorption-mass spectrometry and temperature programmed reaction-mass spectrometry (TPD-TPR-MS), after pre-adsorption of both reactants and products. It was found that phenol forms when N 2 O is adsorbed first, followed by benzene. Almost no phenol formation was observed when adsorbing benzene before N 2 O. Furthermore, on this catalyst N 2 O decomposed since 50°C or less, forming gaseous N 2 and adsorbed oxygen, which started to become available for the oxidation of benzene since 100–200°C. However, the so formed phenol remained adsorbed onto the catalyst. It desorbed within the 225–425°C temperature range, with a maximum around 300°C.