Stable Rh particles in hydrotalcite-derived catalysts coated onFeCrAlloy foams by electrosynthesis

Rh-based structured catalysts for the Catalytic Partial Oxidation of CH4to syngas were prepared by elec-trosynthesis of Rh/Mg/Al hydrotalcite-type compounds on FeCrAlloy foams and calcination. The effectsof Rh content, total metal concentration, and partial replacement of Mg2+by Ni2+in the electrolytic solu-tion on coating thickness, Rh speciation, metallic particle size, and catalytic activity were investigated bySEM/EDS, -XRF/XANES and tests under diluted and concentrated reaction conditions.The amount of Rh species, present as Mg (RhxAl1−x)2O4, depended on the thickness of the electrosyn-thesised layer as well as the Rh particle size and dispersion. Smaller and more dispersed particles wereobtained by decreasing the Rh concentration in the electrolytic solution from Rh/Mg/Al = 11/70/19 to5/70/25 and 2/70/28 atomic ratio% (a.r.%) and in thinner rather than thicker layers. Despite the improve-ment in metallic particles features, the CH4conversion was negatively affected by the low amount ofactive sites in the coating, the high metal support interaction and possibly the oxidation of metallicparticles and carbon formation.A larger amount of solid containing well dispersed Rh particles was deposited by increasing the totalmetal concentration from 0.03 M to 0.06 M with the Rh/Mg/Al = 5/70/25 a.r.%, and the catalytic perfor-mances were enhanced. The partial replacement of Mg2+by Ni2+gave rise to a very active bimetallicRh/Ni catalyst, CH4conversion and selectivity to syngas were above 90%, however, it slightly deactivatedwith time-on-stream.