B–O Oligomers or Ring Species in AlB2: Which is More Selective for Propane Oxidative Dehydrogenation?

B-based catalysts are widely studied in the oxidative dehydrogenation of propane (ODHP) owing to their high selectivity. Correspondingly, two species, B–O oligomers and rings, have been recognized as active centers in B-based catalysts. To answer the essential question of whether B–O oligomers or ring species are more selective for ODHP, two AlB2 catalysts enriched with B–O rings (R-AlB2) and abundant B(OH)xO3–x oligomers (O-AlB2) were designed and compared herein. When tested in ODHP, R-AlB2 exhibits an olefin yield of 30.2% at 500 °C, which is 2.3 times that of O-AlB2. Additionally, R-AlB2 was stable for up to 200 h without deterioration. Multiple characterizations, including in situ Fourier transform infrared spectroscopy and theoretical calculations, demonstrate that B–O rings are more advantageous for producing propylene (C3=) via a dehydration pathway with lower energy barriers and ethylene (C2=) via two other reaction pathways (direct cracking of propane and oxidative coupling of methyl) B(OH)xO3–x is primarily responsible for producing few C3=.