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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]

A series of Pd/Co 3 O 4 catalysts with increasing palladium loading in the range of 0.5–5 wt.% was prepared by incipient wetness impregnation of Co 3 O 4 . Solution combustion synthesis with urea as a fuel was used to optimize the Co 3 O 4 reactive support for palladium in the combustion of methane in lean conditions. The obtained catalysts were thoroughly examined by XRD, XPS, XRF, RS, FESEM, H 2 -TPR, TGA, and N 2 -BET techniques. The catalytic tests of CH 4 combustion were performed for 0.5, 1, and 2 vol.% CH 4 , with constant lambda value. The obtained results revealed that a sub-stoichiometric fuel-to-oxidizer ratio, 0.75, results in the most catalytically active Co 3 O 4 phase. The important differences in the catalysts’ activity were apparent for the highest CH 4 concentration, with the 3% Pd/Co 3 O 4 being the most active catalyst. The observed activity was explained considering the physicochemical, spectroscopic, and microscopic characterization of the catalysts with the PdO nanocrystals surface distribution being the determining factor for the catalysts’ reactivity. A simple model accounting for the observed dispersion effect is proposed. The model is based on a two types of the interaction of the surface PdO active phase with the Co 3 O 4 support. Firstly, cobalt oxide helps to remove hydroxyl species from the PdO surface, thus making the active sites more available for methane activation. Secondly, cobalt spinel provides lattice oxygen to the PdO phase, again helping to recreate active sites thereon. [ABSTRACT FROM AUTHOR]

[Display omitted] • Catalytic performance of 3% PdO/Co 3 O 4 lined on various combinations of ceramic OCF. • Evaluation of apparent kinetic parameters for each foam combination. • Kinetic, external and internal mass transfer resistances: Operating regimes. • Effects of the external and internal heat transfer on combined OCF configurations. • Synergetic effect on catalytic activity with same length OCFs in the order SiC + Zir. 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/Co 3 O 4 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 g cat −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. [ABSTRACT FROM AUTHOR]

• 3% PdO/Co 3 O 4 coated on alumina, silicon carbide, and zirconia open cell foams. • Best catalytic activity belongs to zirconia open cell foam coated with 200 mg on Co 3 O 4. • Importance of the low thermal conductivity of the foam to favor the catalytic reaction. • Catalytic activity decreases slightly after 250 h of time on stream. • STEM analysis for PdO dispersion on fresh/aged zirconia open cell foams. 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 Co 3 O 4 coated on three different OCFs (alumina, silicon carbide and zirconia) was investigated toward the reaction of CH 4 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. [ABSTRACT FROM AUTHOR]