Synergistic Effect Between Ca4v4o14 And Vanadium-Substituted Hydroxyapatite In The Oxidative Dehydrogenation Of Propane.

The present work reports on a new type of V-based catalysts, namely V-substituted hydroxyapatites, and the influence of the synthesis conditions on their catalytic performance in the oxidative dehydrogenation of propane (ODHP) reaction. V-x-substituted hydroxyapatite materials prepared with the periodic addition of ammonia during the maturation step (V-x-HAp-pH-per) were shown to exhibit a Ca4V4O14 phase in addition to the V-substituted hydroxyapatite phase for x greater than or equal to 3.5. TEM characterization of the biphasic samples allowed us to demonstrate that the Ca4V4O14 phase was grown epitaxially on the V-x-HAp nanorods. The close intimacy between the two phases was confirmed by NMR suggesting the involvement of V4+ species. Consistently EPR data of the fresh and spent samples showed that V4+ species may be stabilized at the boundaries of these two phases. The strong promotion of the oxidative dehydrogenation reaction to propene observed from 723 K for the V-4-HAp-pH-per composition is attributed to a synergistic effect between the V-x-HAp nanorods that enable the activation of propane and the Ca4V4O14 phase that helps the redox exchanges. This synergy may be attributed to an easier electron delocalization on the V4O14 units located at the phases' boundaries.