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Electron paramagnetic resonance analysis of La(1-x)M(x)MnO(3+δ) (M = Ce, Sr) perovskite-like nanostructured catalysts.

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.

Oxygen transport in nanostructured lanthanum manganites

Methods and models describing oxygen diffusion and desorption in oxides have been developed for slightly defective and well crystallised bulky materials. Does nanostructuring change the mechanism of oxygen mobility? In such a case, models should be properly checked and adapted to take into account new material properties. In order to do so, temperature programmed oxygen desorption and thermogravimetric analysis, either in isothermal or ramp mode, have been used to investigate some nanostructured La1-xAxMnO3±δ samples (A = Sr and Ce, 20-60 nm particle size) with perovskite-like structure. The experimental data have been elaborated by means of different models to define a set of kinetic parameters able to describe oxygen release properties and oxygen diffusion through the bulk. Different rate-determining steps have been identified, depending on the temperature range and oxygen depletion of the material. In particular, oxygen diffusion was shown to be rate-limiting at low temperature and at low defect concentration, whereas oxygen recombination at the surface seems to be the rate-controlling step at high temperature. However, the oxygen recombination step is characterised by an activation energy much lower than that for diffusion. In the present paper oxygen transport in nanosized materials is quantified by making use of widely diffused experimental techniques and by critically adapting to nanoparticles suitably chosen models developed for bulk materials.

Integrated 5 kW

A power unit constituted by a reformer, a H2 purification section and a fuel cell is being installed c/o the Dept. of Physical Chemistry and Electrochemistry of Universita degli Studi di Milano, on the basis of a collaboration with Helbio S.A. (Hydrogen and Energy Production Systems, supplier) and the support of some sponsors (Linea Energia S.p.A., Parco Tecnologico Padano and Provincia di Lodi). The system is suitable to obtain 5 kWelectric (a.c.) + 5 kWthermal (hot water at 70°C) as peak output. H2 is produced by steam reforming (SR) of second generation bioethanol, obtainable by different non-food competitive biomass. The assessment of the effect of biomass nature and of the consequent different impurities left in the produced bioethanol is part of the experimentation, together with the evaluation of the impact of bioethanol production cost on the final energy cost. Furthermore, the effect of different ethanol/steam ratios will be taken into account to lighten as much as possible the energy demanding ethanol dehydration process. The former point focuses on catalyst life, imposing careful ethanol characterisation and proper catalyst formulation, whereas the latter is connected with the overall energetic efficiency and economic sustainability. Indeed, the reforming process requires co-feeding of water, opening the way to the research of different, cheaper, ethanol purification strategies, leading to lower ethanol concentration with respect to the azeotrope. The reformate is purified from CO down to a concentration below 20 ppm, suitable to feed the proton exchange membrane fuel cells (PEMFC) stack integrated in the fuel processor. This result is achieved by feeding it to two water gas shift reactors, connected in series and operating at high and low temperature, respectively. The expected CO concentration in the outcoming gas is ca. 1 vol% and the final CO removal to meet the specifications is accomplished by selective methanation. The purified H2 is fed to a 5 kWe PEMFC stack, which should have an expected overall efficiency around 80% (including thermal output). The main goal of the present project is to check system performance under widely different operating conditions and load, to verify the effectiveness of the proposed technology and to suggest adequate improvements. Different operating conditions are under evaluation as for ethanol origin, purity, concentration, temperature and space velocity of every reaction step, so to obtain the best compromise between H2 yield, power output and operating costs.Copyright