Electrodeposition of CeO 2 and Pd-CeO 2 on small pore size metallic foams: Selection of deposition parameters

The electrodeposition, in particular the electro-base generation method, is an alternative to conventional washcoating to coat open-cell metallic foams, especially small pore size ones. In this work, the method was applied for the in-situ synthesis of cerium-based coatings, CeO 2 and Pd-CeO 2 , on 100 pores per inch (ppi) FeCrAl foams. The range of parameters suitable for the electrodeposition of CeO 2 films of different thickness and morphology was firstly investigated, i.e. Ce(NO 3 ) 3 concentration, potential applied, and deposition time. Then the most challenging one step Pd-CeO 2 electrodeposition was studied; the Pd content and distribution were optimized considering also the electrochemistry and chemistry of Pd 2+ species, i.e. by selection of a suitable Pd 2+ complex precursor (Pd(NH 3 ) 4 (NO 3 ) 2 or PdCl 2 in HCl). Coated foams were calcined at 550 °C to obtain the structured catalysts. The CO oxidation was used as a model reaction to test the activity of Pd-CeO 2 catalysts. The electrodeposition of cubic fluorite CeO 2 coatings on the surface of the foam ranging from few to 18 μm and made by compact and/or platelet particles was easily achieved and with a high reproducibility. The Pd-CeO 2 samples prepared from the ammine-containing electrolyte, though generated a well-adhered coating, resulted in a lower Pd content than the nominal value of the electrolyte. A high electrolyte concentration containing PdCl 2 combined with a short time allowed to deposit a rather thick Pd-containing CeO 2 coating avoiding the massive Pd° deposition. CO oxidation tests, especially at high flow rates, confirmed the key role of the coating and Pd distribution on the activity of the structured catalysts. A comparison of the conversion in mass transfer regime and estimates with literature correlations was presented, showing that, despite the very complex geometry of the support, a remarkably high quantity of the available surface is effectively exploited, paving the way for compact catalytic converters.