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In this study, kinetic and mass transfer resistances (pore and interphase diffusion) were evaluated by varying the Co3O4 amount in the catalyst (PdO/Co3O4) 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.% CH4 inlet concentration, O2/CH4 molar ratio 8, WHSV 30, 60 and 90 NL h−1 gcat−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 Co3O4 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 Co3O4 amount. Finally, we derived a correlation that describes the mass transfer in OCFs at low Reynolds numbers.

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), H2 temperature programmed reduction, H2O 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 NH3. 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 NH3. 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 CH4, CO, N2O, humidity, O3, CO2 and NO2 at the best operating temperature.

An environmentally friendly auxiliary power unit requires catalysts operating in the cyclic mode, producing H at a steady rate with high CO selectivity and minimum CO clean-up. Here, 1% Pt/CeO catalyst was synthesized using the solution combustion synthesis method and investigated toward methane steam reforming reaction. Preliminary tests were performed by varying the steam-to-carbon ratio (S/C), gas hourly space velocity (GHSV), and time-on-stream (TOS). The catalyst showed near-equilibrium CH conversion and high H concentration (75% dry basis, N-free) obtained at S/C = 2.8 and GHSV = 24 000 h. The catalytic activity was stable after 25 cycles of start-up and shut-down operations, equivalent to 150 h of TOS. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques were used to characterize either the fresh and aged catalyst after 150 h of TOS.

The microstructured reactor concept is very promising technology to develop a compact reformer for distributed hydrogen generation. In this work, a catalytic plate reactor (CPR) is developed and in...

For catalytic process intensification, a series of open cell foams (OCFs) made of silicon carbide (SiC) and zirconia (Zir) with pore density of 30 ppi coated with 3 wt% PdO/Co3O4 as catalyst were combined together and tested toward methane oxidation in lean conditions. In each combination, the SiC OCF was positioned in the reactor on the inlet side of the reactant gases followed by the Zir OCF. The reactor was fed at different weight hourly space velocities (WHSV, 30 and 90 NL h−1 gcat−1) and inlet methane concentrations (0.5 and 1 vol%). The best results are obtained with the combination where two supports of same length but with different thermal conductivity (higher at the inlet of the reactor, SiC, and lower at the outlet, Zir) are used in series. For all OCF combinations, mass transfer effects were evaluated using the characteristic resistances (kinetic, internal and external mass transfer). The external and internal heat transfer effects were analyzed using the Mears and Anderson criteria. Furthermore, a comparison in terms of volumetric heat transfer coefficient and heats of removal/reaction was performed.

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.

In this work a series of cobalt spinel catalysts was synthesized by different methods and doped with 1 wt% of palladium via incipient wetness impregnation or solution combustion synthesis (SCS). Both undoped and Pd-doped spinels were characterized from the structural and surface point of view (XRD, XRF, μRS, BET, FESEM) and tested toward the oxidation of methane in lean conditions, in gas mixtures containing from 0.5 to 2 vol% of CH4. These methane concentrations are typical of processes involving combustion of CH4 in lean conditions as the after-treatment of unconverted CH4 in compressed natural gas-fed vehicle exhausts, or the treatment of fugitive CH4 from leaks in coal mines. The temperature window for the catalytic activity of the undoped Co3O4 materials spread from 350 to 600 °C. The preparation method affected the catalytic activity of undoped Co3O4, with the best catalytic activity related to the spinel prepared by SCS employing urea. The addition of 1 wt% of Pd lowered the temperature window for the catalytic activity to the range of 250–500 °C, with insignificant differences for the various preparation methods. The beneficial effect of Pd-doping was assigned to the enhancement of the reduction of cobalt in the oxide structure.

Coated ceramic open cells foams (OCFs) with catalysts offer an attractive alternative to packed bed reactors for process intensification. Here, the effect of 3 wt% PdO on Co3O4 coated on three different OCFs (alumina, silicon carbide and zirconia) was investigated toward the reaction of CH4 combustion in lean conditions. The OCFs were characterized by Raman spectroscopy and FESEM analysis. The operating regime of each OCF catalyst was investigated using a series of mass transfer resistances assuming pseudo first order reaction (large excess of oxygen). The thermal conductivity of OCFs plays an important role on the overall performance of the combustion reaction in terms of heat and mass transfer. The best OCF structured catalyst was tested up to 250 h of time-on-stream, demonstrating good stability. PdO dispersion over the structured catalyst at the fresh and aged status was assessed by STEM analysis.

Co3O4|α-Al2O3|cordierite structured catalysts were developed, optimizing washcoating procedure, active phase loading, and its deposition method via impregnation and solution combustion synthesis (SCS). The catalysts were thoroughly characterized by XRD, μRS, SEM/EDS, and BET, revealing that the catalyst layer deposited over cordierite carrier, consists of a washcoated micrometric α-Al2O3 (0.1–0.3 µm grains), where spinel nanocrystals (30–50 nm) were uniformly dispersed. It was found out that the SCS method to synthesize and finely disperse spinel nanoparticles results in significant better catalytic performance in low-temperature N2O decomposition than the classic impregnation method. The effectiveness factor evaluated, based on catalyst morphological features and deN2O catalytic results, was found to be ≈1. The determined mass transfer coefficients and type of the catalyst working regime (purely kinetic in the whole temperature range) provide the useful platform for rational design of a real deN2O catalyst.

Solution combustion synthesis (SCS) is a preparation technique that can be used to synthesise a variety of inorganic nanomaterials and structured catalysts. It is based on a self-propagating exothermic redox reaction between organic salts and a fuel mixed together in an aqueous solution which results in the formation nanocrystalline and highly pure solid nanomaterials. SCS can be considered as an attractive synthesis method for catalysts due to the simple nature of the synthesis route and short reaction times. The process is easily scaled up to any kind of application which makes it economically attractive. This mini-review provides a short panoramic overview on the synthesis of structured catalysts by SCS and their recent applications for energy applications and pollution control.