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[Display omitted] • Pore and strut diameter distribution of zirconia open cell foam. • Effect of Co 3 O 4 amount on the catalytic performance for the complete CH 4 oxidation. • Pd-PdO transformation by varying the carrier amount and inlet CH 4 concentration. • Evaluation of kinetic, intraparticle and interphase mass transfer resistances. • Mass transfer correlation for ceramic open cell foam a low Re numbers. In this study, kinetic and mass transfer resistances (pore and interphase diffusion) were evaluated by varying the Co 3 O 4 amount in the catalyst (PdO/Co 3 O 4) supported on the zirconia open cell foam (Zir-OCF) of 30 ppi. The catalytic performance was examined toward the methane combustion in lean conditions (0.5 and 1.0 vol.% CH 4 inlet concentration, O 2 /CH 4 molar ratio 8, WHSV 30, 60 and 90 NL h−1 g cat −1). Pore and strut geometry of the bare foam were evaluated by SEM images and X-CT data analysis. Solution combustion synthesis was employed to line the Co 3 O 4 spinel on the foam, while the wetness impregnation for the PdO on the spinel. The various resistances were evaluated and compared at different WHSV by varying the Co 3 O 4 amount. Finally, we derived a correlation that describes the mass transfer in OCFs at low Reynolds numbers. [ABSTRACT FROM AUTHOR]

The reactivity of a catalytic layer consisting of 3 wt.% of Pd/Co 3 O 4 over an alumina monolith (100 cpsi, diameter 0.9 cm, length 3 cm) and two alumina open cell foams (30 and 45 ppi, diameter 0.9 cm, length 3 cm) was investigated in the oxidation of residual methane in lean conditions. The ceramic structures were coated via solution combustion synthesis (Co 3 O 4 ) and wetness impregnation (Pd). The catalytic reactivity of the catalysts coated on the structured supports was assessed in a gas mixture containing 0.5 or 1 vol.% of methane at different weight hourly space velocities (WHSV, 30 and 60 NL h −1 g cat −1 ). Moreover, the prepared structured catalysts were characterized by measuring the pressure drop and determining the volumetric heat transfer coefficients. Both the WHSV and the characteristics of the support influenced the catalytic activity. In general, open cell foams coated with Pd/Co 3 O 4 show superior catalytic activity than the coated monolith. [ABSTRACT FROM AUTHOR]

Ceramic open cell foams (OCF) are characterized by lower pressure drop, high geometric surface area, and enhanced radial convection in comparison with monolith-type supports. In this work, silicon carbide (SiC) and zirconia (Zir) OCF with different pore per inch (ppi) density were coated with 200 mg of Co3O4 by solution combustion synthesis and doped with 3 wt % of Pd via wetness impregnation. Their catalytic activity was tested toward the lean oxidation of methane at different weight hourly space velocities. Zir OCF with 30 ppi exhibits the best catalytic activity for all reacting conditions, followed by Zir 45 ppi, SiC 45 ppi, and SiC 30 ppi. The better performance of Zir OCF was rationalized considering their lower volumetric heat exchange coefficients, which favor the reaction heat removal by convection via the flue gases. A 200 h stability test on the best structured catalyst demonstrated full methane conversion at a temperature below 400 °C. These results confirm the fundamental role of thermal conductivity of the structured catalysts' support. [ABSTRACT FROM AUTHOR]

Nano-crystalline cobalt spinel was prepared by combustion synthesis and used as ammonia sensing material. After synthesis, the powder was calcined at 600 °C for 4 h and characterized by thermal analysis, X-ray diffraction, Raman spectroscopy, X-ray Photoelectron Spectroscopy, nitrogen adsorption (B.E.T, Brunauer, Emmet, Teller and B.J.H., Barrett, Joyner, Halenda techniques), H 2 temperature programmed reduction, H 2 O adsorption and field emission scanning electron microscopy. Sensors were screen-printed onto α-alumina substrates with platinum interdigitated electrodes and fired at 700 °C for 1 h in air, after drying overnight. The sensor response was measured in the range 150 °C–250 °C under 1–50 ppm of NH 3. Best results were obtained at 225 °C, with R (the ratio between the impedance of the film under gas exposure at the equilibrium and the impedance under dry air) equal to 1.83 under 50 ppm NH 3. Response time and recovery time (e.g., the times taken by the sensor to attain 90% of total impedance change from its initial impedance value) were determined, together with cross-sensitivity tests towards CH 4 , CO, N 2 O, humidity, O 3, CO 2 and NO 2 at the best operating temperature. • Nano-crystalline Co 3 O 4 powder was synthesized by combustion synthesis. • Sensors were screen-printed with the prepared powder. • Thick films could selectively detect 1 ppm ammonia concentration at 225 °C. • Both response and recovery times of the sensor were reasonably fast (few minutes). [ABSTRACT FROM AUTHOR]