CeO2 morphology-dependent NbOx –CeO2 interaction, structure and catalytic performance of NbOx/CeO2 catalysts in oxidative dehydrogenation of propane

• CeO2 morphology strongly affects NbOx–CeO2 interactions and structures of NbOx/CeO2 catalysts.
• Monomeric Nb and Nb4+ species are most abundant respectively on r-CeO2-500 and c-CeO2.
• NbOx suppresses surface reduction of c-CeO2 and r-CeO2-500 but promotes that of r-CeO2-700.
• 0.6Nb/r-CeO2-500 is most active in catalyzing low-temperature ODHP reaction.

A series of NbOx/CeO2 catalysts were synthesized employing CeO2 cubes (c-CeO2), CeO2 rods calcined at 500 °C (r-CeO2-500) and CeO2 rods calcined at 700 °C (r-CeO2-700) as the supports, and their structures and catalytic performances in the oxidative dehydrogenation of propane reaction were studied. Strong CeO2 morphology-dependent NbOx –CeO2 interaction, structure and catalytic performance of NbOx/CeO2 catalysts were observed. The supported NbOx species evolve with the increasing Nb loading from the monomeric Nb species to the polymeric Nb species and the CeNbO4 species. The monomeric Nb5+ species interacting with oxygen vacancy/Ce3+ on CeO2 can be reduced to form the monomeric Nb4+ species. The formed monomeric Nb species follows the order of NbOx/r-CeO2–500 > NbOx/c-CeO2 > NbOx/r-CeO2-700 while the formed monomeric Nb4+ species is most abundant on the c-CeO2 support. The loading of NbOx suppresses the surface reduction of c-CeO2 and r-CeO2-500 but promotes the surface reduction of r-CeO2-700. R-CeO2-500 and r-CeO2-700 are more catalytic active than c-CeO2 in the oxidative dehydrogenation of propane reaction. The loading of NbOx slightly enhances the catalytic activity of c-CeO2 but decreases the catalytic activity of r-CeO2-700. A loading of 0.6 Nb/nm2 much enhances the catalytic activity of r-CeO2-500 at 200 °C, but further increasing the Nb loading results in the decrease of the C3H8 conversion. These results add a solid example to vindicate the morphology engineering strategy to modify the structure and catalytic performance of CeO2-based catalysts.

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