Improvement in the coating homogeneity in electrosynthesized Rh structured catalysts for the partial oxidation of methane

The precipitation of Rh/Mg/Al and Rh/Al hydroxides on the surface of FeCrAlloy foams by a base elec-trogeneration method was investigated to improve the properties of the deposited film (homogeneityand composition) and therefore the performances of the structured catalysts, obtained by calcination,in the Catalytic Partial Oxidation of CH4to syngas. The work focussed on decreasing current gradientswithin open-cell foam cylinders by increasing the number of electrical contacts from 1 to 3 points to pro-mote a more homogeneous precipitation of the hydroxides. Electrochemical and catalytic tests as wellas SEM/EDS and -XRF/XRD analyses allowed to correlate the effect of the number of electrical contactpoints with materials properties. Lastly, syntheses were performed on Pt plates to study the effect of theelectrical behaviour and shape of the support on the composition of the film.A more homogeneous coating of the foam surface was achieved by adopting a configuration with 3contact points since the reduction of nitrates and water molecules that generates the basic media in thevicinity of the support was enhanced. Layer thicknesses up to 5–15 m were deposited; however, thesequential precipitation of a film with composition closer to the expected one and a layer enriched in Aland Rh (outer layer) was not avoided. The improvement in the coating gave rise to enhanced perform-ances for a sample prepared at −1.1 V for 3000 s. Contrarily, the low adherence of the outer layer in asample prepared at −1.2 V for 2000 s during both calcination and catalytic tests may be responsible ofthe unexpected decrease in catalytic performances. The same sequential precipitation was observed byperforming the syntheses on Pt plates, showing that the electrical nature the support did not play a keyrole on this phenomenon.