Catalysis Today, Vol.334, 37-47, 2019
Electrodeposition of CeO2 and Pd-CeO2 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, CeO2 and Pd-CeO2, on 100 pores per inch (ppi) FeCrAl foams. The range of parameters suitable for the electrodeposition of CeO2 films of different thickness and morphology was firstly investigated, i.e. Ce(NO3)(3) concentration, potential applied, and deposition time. Then the most challenging one step Pd-CeO2 electrodeposition was studied; the Pd content and distribution were optimized considering also the electrochemistry and chemistry of Pd2+ species, i.e. by selection of a suitable Pd2+ complex precursor (Pd(NH3)(4)(NO3)(2) or PdCl2 in HCl). Coated foams were calcined at 550 degrees C to obtain the structured catalysts. The CO oxidation was used as a model reaction to test the activity of Pd-CeO2 catalysts. The electrodeposition of cubic fluorite CeO2 coatings on the surface of the foam ranging from few to 18 mu m and made by compact and/or platelet particles was easily achieved and with a high reproducibility. The Pd-CeO2 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 PdCl2 combined with a short time allowed to deposit a rather thick Pd-containing CeO2 coating avoiding the massive Pd degrees 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.