P. Del Gallo

Electrical properties of dense Me-doped bismuth vanadate (Me=Cu, Co) pO2-dependent conductivity determined by impedance spectroscopy

Co- and Cu-substituted Bi4V2O11 compounds were synthesised by means of fine reactive powders with a typical d50 close to 0.5 μm. Appropriate sintering conditions resulted in fine and homogeneous microstructure without any cracks related to large grain size. The total electrical conductivity was measured by complex impedance spectroscopy with respect to temperature, oxygen partial pressure, thermal history, and nature of dopant. The bulk and the grain boundary conductivity were also studied for both compounds. No time-dependence and no thermal hysteresis of the total electrical conductivity were observed and a structure dependence of the electrical properties was noticed. BICUVOX0.10 material can be considered as a pure oxide ion conductor within the investigated experimental conditions whereas BICOVOX0.10 exhibited a p-type conductivity contribution to the bulk conductivity with an ionic transference number greater than 0.97.

Deactivation of a Pt/γ-Al2O3 catalyst in the partial oxidation of methane to synthesis gas

The deactivation of a Pt/-Al2O3 catalyst used in an industrial plant for the partial oxidation of methane to synthesis gas was investigated. Four samples at different time-on-stream in air were characterized and their catalytic performances were tested in a micro-reactor in order to shed light on the causes and the effects of this deactivation. The high temperatures (about 900 ◦ C) reached while operating in the industrial plant, promoted modifications to the -Al2O3, inducing sintering phenomena and, therefore, deactivation effects. The not used sample showed good values of yield in syngas (compared with equilibrium values), but these performances decreased quickly with time-on-stream.

Redox stability of BIMEVOX.10 materials (ME=Co, Cu)

Abstract Redox stability of BIMEVOX.10 compounds (ME=Co, Cu) was studied using a technique involving electrochemical reduction followed by open-circuit (o.c.) relaxation. BICUVOX.10 and BICOVOX.10 were irreversibly reduced below −375 mV versus air and −530 mV versus air, respectively. Reaction paths were identified from thermodynamical considerations and Wavelength Dispersive Spectroscopy.

Oxygen diffusion coefficient and oxygen exchange coefficient of BIMEVOX.10 (ME=Cu, Co) ceramic membranes

Abstract The 18 O/ 16 O Isotope Exchange Depth Profile technique (IEDP) was applied to BIMEVOX.10 (ME=Cu, Co) materials to determine their oxygen exchange coefficients and bulk oxygen tracer diffusion coefficients. These results are compared to the exchange current densities obtained from current–voltage curves and bulk conductivity determined by impedance spectroscopy. These results confirm that, in spite of a noticeably higher ionic conductivity than that of the classical oxide electrolytes such as yttria stabilized zirconia (YSZ) or gadolinia-doped ceria (GDC), the oxygen surface exchange coefficients are low.

SiC as stable high thermal conductive catalyst for enhanced SR process

1. Abstract Silicon carbide has been chosen as a support for steam methane reforming (SMR). In fact, its good conductive properties may improve the temperature profile, while decreasing the high AT caused by the high endothermicity of the reaction and, at the same time, increasing the heat transfer from external furnace, reactor wall and catalyst particles. 10 wt % Ni was deposited on the SiC support by incipient wetness impregnation. The sample was calcined at different temperatures in order to study both the chemical-physical properties and the interaction between the support and active phases. The sample calcined at 700°C was tested in a SMR laboratory plant under different operative conditions, in order to evaluate the activity and stability with time-on-stream. On a laboratory scale, the catalyst shows good results, although, at very high temperatures (960°C) the support shows a slight SiO 2 formation.

In Situ IR Characterization of CO Interacting with Rh Nanoparticles Obtained by Calcination and Reduction of Hydrotalcite-Type Precursors

Supported Rh nanoparticles obtained by reduction in hydrogen of severely calcined Rh/Mg/Al hydrotalcite-type (HT) phases have been characterized by FT-IR spectroscopy of adsorbed CO [both at room temperature (r.t.) and nominal liquid nitrogen temperature] and Transmission Electron Microscopy (TEM). The effect of reducing temperature has been investigated, showing that Rh crystal size increases from 1.4 nm to 1.8 nm when the reduction temperature increases from 750°C to 950°C. The crystal growth favours the formation of bridged CO species and linear monocarbonyl species with respect to gem-dicarbonyl species; when CO adsorbs at r.t., CO disproportionation occurs on Rh and it accompanies the formation of (CO)2. The role of interlayer anions in the HT precursors to affect the properties of the final materials has been also investigated considering samples prepared from silicate-instead of carbonate-containing precursors. In this case, formation of (CO)2 and CO disproportionation do not occur, and this evidence is discussed in terms of support effect.

New catalysts for the syngas production obtained by hydrotalcite type precursor containing silicate

Publisher Summary Ni and/or Rh based catalysts (ex-HT) derived by hydrotalcite precursor are considered to be effective catalysts in the catalytic partial oxidation (CPO) reaction. This chapter discusses new stable ex-HT catalysts prepared by inserting silicate instead of CO 3 2- anions in the interlayer. The amount of silicates is not limited by the charge balance of the cations, because, an excess of silicates leads to the formation of polysilicate anions. The insertion of silicates affects the structure of the calcined samples, because, unlike CO 3 2- , the silicates remain in the structure and contribute to the formation of the final catalysts. Catalysts with innovative structure are obtained by HT precursor prepared using silicate as interlayer anion. The calcined catalysts showed two phases—a mixed oxide type structure and a new M-silicate structure, where the cations of the active metal are partially soluted. The Rh catalyst prepared by HT silicate was more active and selective than the one prepared by CO 3 2- .