Modulating kinetic regimes in oxidative dehydrogenation of propane via subsurface metal-mediated dynamic BO-H bond dissociation and regeneration

Subsurface metal promoted boron-based catalysts (M@BO x ) have demonstrated excellent activity and olefin selectivity in the oxidative dehydrogenation of propane (ODHP) through the efficient regulation of the special radical pathways. In this study, we discovered convincing subsurface metal dependent kinetic behaviors of the M@BO x catalysts which serve as powerful evidence to interpret the function of subsurface metal promoters in the ODHP reaction. The dependence of reaction rate with the partial pressure of propane and oxygen was determined and significant change of kinetic behaviors was resolved with the change of metal promoters, including the propane reaction order ranging from 1.93 to 2.44 and the turning O 2 pressure in the rate- P O2 profiles. Based on the kinetic equations derived from the reaction mechanism and the steady-state approximation, subsurface metal promoters modulate the contributions of surface and gas-phase reactions by influencing the initiation of reactive radicals both on the surface and in the gas phase. The reaction order of propane is positively correlated with the ratio of BO-H dissociation/regeneration rates ( k 1 / k 2 ), but high catalytic ODHP performance can only be realized at an appropriate k 1 / k 2 ratio. Similar trend is also observed regarding the partial pressure of oxygen. Therefore, the kinetic studies experimentally demonstrate the strong ability of subsurface metal in changing the radical initiation behaviors of supported boron oxide active species, pointing out that balancing the O-H bond dissociation and regeneration rates are highly important to achieve high performance in ODHP reaction.