Preferential oxidation of CO in excess of H₂ on Pt/CeO₂-Nb₂O₅ catalysts

A series of CeO₂ -Nb₂ O₅ mixed oxides with different Nb content, as well as the pure oxides, have been synthesized by co-precipitation with excess urea. These materials have been used as supports for platinum catalysts, with [Pt(NH₃) 4](NO₃)₂ as precursor. Both supports and catalysts have been characterized by several techniques: N2 physisorption at 77 K, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, scanning electron microscopy, transmission electron microscopy, temperature-programmed reduction and temperature-programmed desorption (CO and H₂), and their catalytic behaviour has been determined in the PROX reaction, both with an ideal gas mixture (CO, O₂ and H2) and in simulated reformate gas containing CO₂ and H₂O. Raman spectroscopy analysis has shown the likely substitution of some Ce⁴⁺ cations by Nb⁵⁺ to some extent in supports with low niobium contents. Moreover, the presence of Nb in the supports hinders their ability to adsorb CO and to oxidize it to CO₂. However, an improvement of the catalytic activity for CO oxidation is obtained by adding Nb to the support, although the Pt/Nb₂O₅ catalyst shows very low activity. The best results are found with the Pt/0.7CeO₂-0.3Nb₂O₅ catalyst, which shows a high CO conversion (85%) and a high yield (around 0.6) after a reduction treatment at 523 K. The effect of the presence of CO₂ and H₂O in the feed has also been determined.