Elisabetta Finocchio

Surface and structural characterization of CexZr1-xO2 CEZIRENCAT mixed oxides as potential three-way catalyst promoters

The textural and structural properties of high specific surface area (HS) CexZr1-xO2 mixed oxides (CeZrMO) and their modification upon thermal aging have been investigated. Results from BET area determination and complete porosity analysis, as well as high-resolution electron microscopy, XRD, Raman and FTIR spectroscopies are presented. Some relationships between the molar composition of the binary systems and their textural and structural properties are presented. In addition, it has been possible to propose an explanation for structural features of the mixed oxides (solid-solution structures and possible phase segregation) as a function of Ce content, a point of great interest for the knowledge of phase composition and stability of CeZrMO.

On the role of acidity in catalytic oxidation

Abstract The role of the catalyst surface acid-base properties on the heterogeneously-catalyzed oxidation reaction mechanisms is discussed. Acid-base properties depend on the covalent/ionic character of the metal-oxygen bonds and are involved in some steps of the oxidation reactions, such as the activation of the CH hydrocarbon bonds, the step associated with the evolution of alkoxide species and the desorption/overoxidation of the partial oxidation products. Thus they participate with the cation redox properties in determining the selective/unselective catalyst behavior.

FTIR studies on the selective oxidation and combustion of light hydrocarbons at metal oxide surfaces. Part 2.—Propane and propene oxidation on Co3O4

The interaction of propane and propene and of C3, C2 and C1 oxygenates (propane-1-ol, propan-2-ol, allyl alcohol, acetone, propanal, acrolein, acrylic, propionoic, acetic and formic acids and CO2) on oxidized Co3O4 +x has been studied by FTIR spectroscopy, with the aim to collect data on the mechanism of hydrocarbon catalytic combustion. Propene is already oxidized to acrylate species at RT and burns completely starting from 473 K. Propane already gives rise to acetate, propanoate and acrylate species below 373 K. A reaction scheme for catalytic propane oxidation is proposed. The behaviour of Co3O4 +x combustion catalyst surfaces are compared with those of MgCr2O4 +x, previously investigated. In both cases nucleophilic oxygen species (lattice O2– anions at the oxidized surface) are thought to be involved in catalytic combustion, which occurs via overoxidation of adsorbed partially oxidized compounds.

Characterization and hydrocarbon oxidation activity of coprecipitated mixed oxides Mn3O4/Al2O3

Abstract The surface and redox properties of the manganese oxides Mn3O4 (hausmannite), Mn2O3 (bixbyite) and MnO2 (pyrolusite) and of coprecipitated manganese aluminum Mn3O4/Al2O3 mixed oxide catalysts have been investigated by FT-IR spectroscopy of adsorbed probe molecules methanol and pyridine. Methoxy groups interacting with Mn3+, Mn2+ and Al3+ cations are well distinguishable with respect to the position of their C–O stretching band. The evolution of methoxy groups to formate species allows to obtain information on the reducibility of the surfaces. Also pyridine allows to distinguish such sites and to evaluate their surface acidity. The results concerning the catalytic oxidation of propane over these materials are discussed in relation to their surface properties. The effect of bulk oxygen diffusion rate on the catalytic oxidation rate is evident.

Transition metal mixed oxides as combustion catalysts : preparation, characterization and activity mechanisms

Abstract A number of transition metal mixed oxides with spinel-type, corundum-type and perovskite-type structures have been prepared and characterized. Attempts have been made to improve their morphological properties and their stability. Some of them have been tested in the catalytic combustion of methane, CO and H 2 (perovskites), of propane and of phenantrene. FT-IR experiments allowed to obtain a quite complete picture of the mechanism of catalytic combustion of C3 organic compounds on spinel-type oxides MgCr 2 O 4 and Co 3 O 4 . Nucleophilic oxygen species (lattice oxygen) is thought to be involved in both partial and total oxidation.

IR studies on the activation of C–H hydrocarbon bonds on oxidation catalysts

Abstract The total oxidation of propane and its oxy-dehydrogenation to propene have been studied on spinel-type catalysts Mn3O4, Co3O4 and MgCr2O4 in a flow reactor and in an IR cell. Analogous studies have been performed on the oxy-dehydrogenation of n-butenes to 1,3-butadiene over MgFe2O4. Information on the reaction mechanism have been reached. The activation of the hydrocarbons is thought to occur by abstraction of a hydrogen from the weakest C–H bond, with a simultaneous reduction of a surface site and with the formation of a surface alkoxy-group.

IR study of alkene allylic activation on magnesium ferrite and alumina catalysts

The interaction of propene and butenes with a butene oxydehydrogenation catalyst, MgFe2O4, and with an isomerization catalyst, γ-Al2O3, have been studied by FTIR spectroscopy. Allyloxy species (prop-2-en-1-oxides from propene and but-3-en-2-oxide from but-1-ene) were observed over MgFe2O4, while allyl species (prop-2-en-1-yl from propene, but-3-en-2-yl from but-1-ene and 2-methylprop-2-en-1-yl from isobutene), thought to be σ-bonded to Al3+ ions, were observed over γ-Al2O3. It is proposed that in all cases the allylic C—H bond is heterolytically broken at cation–anion couples (Mn+O2–) to give rise to anionic allyls. However, when the cation is reducible, as on the Fe3+ centres of magnesium ferrite, the allyl anion is further rapidly oxidized to allyloxy species that, at high temperature, can act as cationic allyls which interact weakly with oxide anions. From propene, the cationic allyls can act as symmetric species, as is expected for acrolein synthesis.

Reactivity of Keggin-type heteropolycompounds in the oxidation of isobutane to methacrolein and methacrylic acid: Reaction mechanism

Abstract The oxidation of isobutane to methacrolein and methacrylic acid over a Keggin-type heteropolycompound of composition K 1 (NH 4 ) 2 PMo 12 O 40 Fe 1 O 1.5 was studied in both flow reactor studies and with FT-IR spectroscopy of species which develop at the surface. In both cases either isobutane or possible reaction intermediates were used as probe molecules. It is proposed that the activation of the isobutane at the tertiary CH bond leads to the formation of an alkoxy species, which is then converted to an allylic alkoxy species, precursor for the formation of methacrolein and methacrylic acid. The mechanism proposed explains the experimental evidence relative to the absence of isobutene among the reaction products, and the parallel pathways to the two products. Competitive pathways are the formation of acetic acid, maleic anhydride and carbon oxides.

A study of the abatement of VOC over V2O5-WO3-TiO2 and alternative SCR catalysts

Abstract The conversion of C3 organic compounds (propane, propene, 1- and 2-propanol, allyl alcohol, propanal, acrolein, acetone and 1- and 2-chloropropane) in the presence of excess oxygen has been investigated over two V–W–TiO2 commercial SCR catalysts differing in the V content and over Mn–TiO2 alternative SCR catalysts. V–W–Ti catalysts show poor activity in the oxidation of hydrocarbons and oxygenates and give significant amounts of partial oxidation products. Moreover they give rise to CO in excess of CO2. The sample higher in V is more active. Mn–TiO2 is definitely more active in oxidation of hydrocarbons and oxygenates, and produces, at total conversion, CO2 as the only detectable product. V–W–Ti catalysts are very active in dehydrochlorination of the two 2-chloropropane isomers and retain the same oxidation activity also in the presence of HCl. On the contrary, Mn-based catalysts in the presence of chlorocarbons convert into dehydrochlorination catalysts but lose their catalytic activity in oxidation. V–W–Ti catalysts can be used in Cl-containing atmospheres while Mn–TiO2 can be proposed for DeNOx and VOC abatement in Cl-free atmospheres such as for diesel engine exhaust gas purification.

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.