Kinetic investigations of oxidative dehydrogenation of propane on boron oxide in confined spaces

Oxidative dehydrogenation of propane (ODHP) is a promising process for on-purpose propylene production with favorable thermodynamics. Boron-based catalysts exhibit high alkene selectivity in ODHP, but the understanding of catalytic mechanism remains incomplete, especially regarding the observed supra-linear reaction order of alkanes. In this work, we studied the impact of spatial confinement on the performance and kinetics of boron oxide supported on silica with different pore structures. The formation rate of propylene decreases with the degree of confinement of active boron sites derived from the support. Intriguingly, the apparent activation energy increases with the ODHP activity, and exhibits a positive correlation with the apparent propane reaction order. The apparent propane order of B2O3/SiO2 varies from 1 to 3, which is impacted by pore structure of supports, loading of B2O3, and partial pressure of propane. The trend in propane reaction order and apparent activation energy on B2O3 can be rationalized by the rate expression derived based on the proposed radical chain mechanism with three distinct pathways of propane activation.