F. Deganello

Chemical-physical properties of spinel CoMn2O4 nano-powders and catalytic activity in the 2-propanol and toluene combustion: Effect of the preparation method

Spinel-type CoMn2O4nano-powders are prepared using sol-gel auto combustion (SGC) and co-precipitation (CP) methods and their catalytic activities are evaluated in combustion of 2-propanol and toluene. The chemical-physical properties of the oxides are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2-adsorption-desorption, temperature programmed reduction (TPR) and scanning electron microscopy (SEM). After calcination at 700°C, CoMn2O4-SGC shows higher amounts of the normal-type spinel phase and is more crystalline than CoMn2O4-CP. Higher calcination temperatures (850°C) do not affect very much the weight percentage of the normal-type spinel phase; although the crystal size slightly increased. The TPR analysis evidences a large number of Mn3+ cations in CoMn2O4-SGC compared to CoMn2O4-CP. This difference, together with the higher surface area, could justify the higher activity of CoMn2O4-SGC in both the investigated reactions.

Cathode Performance of Nanostructured La1 − a Sr a Co1 − b Fe b O3 − x on a Ce0.8Sm0.2O2 Electrolyte Prepared by Citrate-Nitrate Autocombustion

Nanostructured La 1-a Sr a Co 1-b Fe b O 3-x (a = 0.3-0.5; b = 0-0.2) and Ce 0.8 Sm 0.2 O 2 powders were successfully prepared by citrate-nitrate autocombustion synthesis and were characterized by scanning electron microscopy and X-ray diffraction analysis. Electrochemical impedance spectroscopy measurements on symmetric cells were performed to evaluate the applicability of La 1-a Sr a Co 1-b Fe b O 3-x as a cathode material for intermediate temperature solid oxide fuel cells based on Sm doped-ceria electrolytes. Our results demonstrated that strontium has a positive effect while iron shows a slightly negative effect on the interfacial resistance. The effect of the electrode sintering temperature was investigated by varying the temperature from 850 to 1250°C, and the best sintering temperature was found to be 900°C. The best characteristics as cathode at intermediate operating temperatures were found for the composition with a = 0.4 and the minimum iron doping, b = 0.05; at 700°C, an area specific resistance of 0.13 Ω cm 2 was measured.

A new, sustainable LaFeO3 material prepared from biowaste-sourced soluble substances

For the first time, sustainable LaFeO3 powders were prepared from soluble bio-based substances (SBO) extracted from urban wastes. For the preparation of the perovskite-type powders, a modified solution combustion synthesis route was used, where SBO have the triple role of fuel, complexant and microstructural templates. A careful examination of the LaFeO3 powders, using complementary characterization techniques, evidenced their peculiar microstructural, morphological, textural and photocatalytic properties. Preliminary photodegradation tests of a phenol-based wastewater pollutant and photobleaching of a model dye were performed on the waste-derived and reference LaFeO3 powders; the obtained results encourage further studies on the application of these materials as heterogeneous catalysts for wastewater treatment. Moreover, a meaningful amount of entrapped matter was evidenced in the powders, which is responsible for most of their peculiar properties.

Strontium and iron-doped barium cobaltite prepared by solution combustion synthesis: exploring a mixed-fuel approach for tailored intermediate temperature solid oxide fuel cell cathode materials

Ba0.5Sr0.5Co0.8Fe0.2O3–δ (BSCF) powders were prepared by solution combustion synthesis using single and double fuels. The effect of the fuel mixture on the main properties of this well-known solid oxide fuel cell cathode material with high oxygen ion and electronic conduction was investigated in detail. Results showed that the fuel mixture significantly affected the area-specific resistance of the BSCF cathode materials, by controlling the oxygen deficiency and stabilizing the Co2+ oxidation state. It was demonstrated that high fuel-to-metal cations molar ratios and high reducing power of the combustion fuel mixture are mainly responsible for the decreasing of the area-specific resistance of BSCF cathode materials. Moreover, a new metastable monoclinic phase with Ba0.5Sr0.5CO3 composition was discovered in the as-burned BSCF powders, enlarging the existing information on the BSCF phase formation mechanism.

Time-resolved X-ray powder diffraction on a three-way catalyst at the GILDA beamline.

Time-resolved X-ray diffraction experiments carried out at the beamline BM08-GILDA of ESRF allowed a study of the structural modifications taking place in a Pt/ceria-zirconia catalyst while the CO oxidation reaction was in progress. The capillary tube in which the sample is stored acts effectively as a chemical microreactor that ensures homogeneity of the sample treatments and minimization of diffusion effects. During the flowing of the reactant CO/He mixture, the investigated catalyst undergoes a fast Ce(IV)-Ce(III) partial reduction that involves the release of one O atom for every two reduced Ce cations. Because Ce(III) has a larger ionic radius than Ce(IV), the structural modification produces an increase of the lattice constant of the ceria-zirconia mixed oxide, and this increase is monitored by the translating imaging-plate device implemented at GILDA. The CO(2) resulting from the oxidation of the fluxed CO is monitored by a quadrupole mass spectrometer during the recording of the time-resolved X-ray diffraction pattern. The chemical and structural information was combined to show that the CO(2) yield is nearly constant until the catalytic system can provide oxygen for the reaction, while the structural rearrangement of the catalyst is delayed with respect to the switching on of the CO/He flux. After this induction time, during which CO(2) is produced with no structural modification of the catalyst, a fast increase of the lattice constant takes place.

Hydrogen tunneling in the perovskite ionic conductorBaCe1−xYxO3−δ

We present low-temperature anelastic and dielectric spectroscopy measurements on the perovskite ionic conductor BaCe(1-x)Y(x)O(3-x/2) in the protonated, deuterated and outgassed states. Three main relaxation processes are ascribed to proton migration, reorientation about an Y dopant and tunneling around a same O atom. An additional relaxation maximum appears only in the dielectric spectrum around 60 K, and does not involve H motion, but may be of electronic origin, e.g. small polaron hopping. The peak at the lowest temperature, assigned to H tunneling, has been fitted with a relaxation rate presenting crossovers from one-phonon transitions, nearly independent of temperature, to two-phonon processes, varying as T^7, to Arrhenius-like. Substituting H with D lowers the overall rate by 8 times. The corresponding peak in the dielectric loss has an intensity nearly 40 times smaller than expected from the classical reorientation of the electric dipole associated with the OH complex. This fact is discussed in terms of coherent tunneling states of H in a cubic and orthorhombically distorted lattice, possibly indicating that only H in the symmetric regions of twin boundaries exhibit tunneling, and in terms of reduction of the effective dipole due to lattice polarization.

EXAFS study of ceria-lanthana-based TWC promoters prepared by sol-gel routes

Extended X-ray absorption fine structure (EXAFS) experiments at the Ce K- and La K-edges were performed on ceria–lanthana–alumina three-way catalysts promoters prepared by sol–gel routes, in order to investigate the effect of lanthanum doping on the ceria structure. The formation of Ce1−xLaxO2−x/2 solid solution, already observed by X-ray diffraction, was confirmed by EXAFS analysis, while no experimental evidence of a Ce–Al interaction was found. In presence of cerium and aluminum, lanthanum is involved in the formation of solid solution with CeO2 and of La–Al compounds. When the La:Al molar ratio is sufficiently high, the growth of a tridimensionally ordered LaAlO3 perovskite compound is observed. For increasing values of x/1−x in the solid solution Ce1−xLaxO2−x/2, the Ce–O distance decreases, while La–O distance remains nearly constant.

Synthesis, characterization and environmental application of silica grafted photoactive substances isolated from urban biowaste

A waste-derived photoactive substance sourced from the green fraction of urban refuses (CVT230) was immobilized on different types of silica support, one amorphous and the other two with controlled porosity (HMS and SBA). In this fashion, three hybrid systems were obtained, which contained CVT230 as an insoluble photoactive component. They were tested in the photodegradation of 4-methylphenol in aqueous solution irradiated by simulated solar light and results showed that they are able to promote the total photodegradation of the pollutant. The materials, both before and after irradiation, were characterized by high-resolution transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), N2 gas-volumetric adsorption, infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The SBA silica hybrid system showed the best performance in terms of stability and reusability, after multiple irradiation cycles. This behaviour can be correlated to the silica morphology and texture, being capable to better allocate and stabilize the CVT230 molecules.

A new in situ methodology for the quantification of the oxygen storage potential in perovskite-type materials

A well known perovskite-type material, LaFeO3, was prepared by citrate–nitrate auto-combustion synthesis and used to formulate a new in situ approach for the analytical evaluation of the redox properties of this class of material. Carbon monoxide was used as a reducing agent-probe, while molecular oxygen was used as an oxidizing agent-probe. In situ FTIR spectroscopy was applied for a qualitative characterization of the interaction probe-material, and microgravimetry was used in order to quantify the extent of the interaction. The results obtained indicated that simple molecules, such as CO and O2, are able to define the redox properties of the material without inducing any important modification as in the case of the more classical temperature-programmed reduction and oxidation methods. The described procedure can be successfully applied for the evaluation of the oxygen mobility/availability and storage potential of other perovskite-type materials.

Effect of O vacancies on the Young’s modulus of the BaCe1−xYxO3−δ perovskite

The effect of oxygen vacancies on the elastic properties of BaCe0.9Y0.1O3−δ is studied by measuring the complex Young’s modulus between 80 and 850 K varying the content of O vacancies from 0 to nearly 0.05. The Young’s modulus measured at a fixed temperature above 300 K may change by more than 20% but this is due to a shift of the rhombohedral-orthorhombic transition by 250 K and to proton and vacancy hopping. Below 100 K these effects are frozen and the filling of the O vacancies with OH ions increases the Young’s modulus by ∼1.3%.