Dynamic Self-Dispersion of Aggregated Boron Clusters into Stable Oligomeric Boron Species on MFI Zeolite Nanosheets under Oxidative Dehydrogenation of Propane

Boron-containing zeolites have been demonstrated as active catalysts for oxidative dehydrogenation of propane (ODHP) to propene. The challenge is that the origin of the boron active sites remains an unsolved issue. In this study, self-pillared boron-containing MFI zeolite nanosheets with an ultrathin b-axis were synthesized, which exhibited low-temperature activity and stability in the ODHP process. A combination of in situ diffuse reflectance infrared Fourier transform, two-dimensional B-11 multiple-quantum MAS NMR, and B-11{H-1} dipolar-heteronuclear multiple-quantum correlation NMR measurements revealed that the MFI zeolite nanosheets with the characteristics of a high specific surface area and abundant Si-OH groups allowed dynamic self-dispersion of highly mobile boron clusters through condensation with surrounding Si-OH groups. The increased number of stable and dispersed oligomeric boron species was responsible for the enhanced catalytic performance and stability in the ODHP process. The catalysts were active at a temperature as low as 390 degrees C. Upon raising the temperature to 430 degrees C, a propane conversion of 14.1% could be achieved together with a selectivity of 80.1% toward all olefins.