Coprecipitated-like hydrotalcite-derived coatings on open-cell metallic foams by electrodeposition: Rh nanoparticles on oxide layers stable under harsh reaction conditions

Structured catalysts based on open-cell metallic foams coated by a catalytic film offer a great potential for intensification and optimization of catalytic processes. Here, we demonstrated the feasibility of the electrodeposition to synthesize in situ and quick Rh/Mg/Al hydrotalcite-type (HT) syngas catalyst precursors with controlled composition, morphology and thickness around 5 to 20 mu m on the surface of FeCrAlloy foams using a two-compartment flow electrochemical cell. After calcination at 900 degrees C, catalytic coatings with properties similar to those of conventional co-precipitated HT-derived catalysts were identified by synchrotron nano-XRF/XRD tomography and HRTEM. The resulting structured catalysts, therefore, merged the properties of both HT-derived catalysts and open-cell foams, namely, thermally stable nano MgO- and spinel-type phases where Rh was dispersed and stabilized against sintering, and high mass and heat transfer. Moreover, the development of a MgAl2O4 thin film in the support-coating interface, by chemical reaction between Mg2+ from the coating and Al3+ from the support during calcination, increased the catalyst adhesion. Consequently, active and stable performance was obtained under harsh reaction conditions in the catalytic partial oxidation of CH4 to syngas as a model reaction. Even in the catalysts operating under severe reaction conditions for about 50 h, the coating was stable and Rh metallic nanoparticles around 2 nm were still well dispersed.