Synergistic Effect Between Ca 4 V 4 O 14 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 Ca 4 V 4 O 14 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 Ca 4 V 4 O 14 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 V 4+ species. Consistently EPR data of the fresh and spent samples showed that V 4+ 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 Ca 4 V 4 O 14 phase that helps the redox exchanges. This synergy may be attributed to an easier electron delocalization on the V 4 O 14 units located at the phases’ boundaries.