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 degrees 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 =.

Automated summary

This study designed two aluminum boron catalysts, R-AlB2 enriched with B-O rings and O-AlB2 enriched with B(OH)xO3-x oligomers, and found that R-AlB2 exhibited a higher selectivity of 30.2% in the high-temperature oxidative dehydrogenation of propane (ODHP), and remained stable for up to 200 hours. Multiple characterizations indicated that B-O rings were more advantageous for the production of propylene (C3=) via a dehydration pathway with lower energy barriers, while B(OH)xO3-x was primarily responsible for producing a small amount of C3=.