Performance Descriptor of Subsurface Metal-Promoted Boron Catalysts for Low-Temperature Propane Oxidative Dehydrogenation to Propylene

Abstract

Boron-based catalysts have exhibited excellent olefin selectivity in the oxidative dehydrogenation of propane (ODHP) reaction. The substrate material should be a potential platform for performance modulation of boron catalysts in this reaction since the introduction of subsurface Ni promoters significantly improves the activity. In this study, we deciphered the substrate effect and identified a performance descriptor to comprehend the roles of subsurface materials in BO_x/metal/BN ODHP catalysts by evaluating different metal promoters. Performance evaluation and transient infrared spectroscopic experiments demonstrate that the intrinsic activity and kinetic behaviors of the O–H bond dissociation/regeneration on the metal-promoted BO_x overlayer are metal substrate-dependent. Combining density functional theory (DFT) calculations, it is found that the dissociation/regeneration inclination of the O–H bond in BO_x(OH)_3–x active species is controlled by the affinity of H for boron oxide species. The metal-O binding energy, which has been demonstrated to be linearly correlated with H affinity, can serve as a straightforward performance descriptor for both low-temperature radical initialization and ODHP reaction, revealing this reaction is controlled by the Sabatier principle, and moderate metal-O binding energy is essential for achieving remarkable performance in the BO_x/M/BN catalysts. Following the guidance of a potential descriptor, Ni–Rh alloy substrates are investigated and the substrate with a Ni/Rh molar ratio of 15:1 significantly enhances the low-temperature intrinsic activity of the metal-modified BO_x to 9.26 μmol/(m²·s), which reaches 105.9 times that of h-BN and is 18.3% larger than the monometallic BO_x/Ni/BN catalysts.