Promoting Catalytic Activity of Boron by Phosphor in Propane Oxidative Dehydrogenation

Abstract

Metal-free boron-containing materials show excellent performance in the oxidative dehydrogenation of propane (ODHP) reaction, while it remains unclear how the composition of the materials may influence their catalytic activity. Herein, by using boron phosphide (BP) as the test bed, a density functional theory study of the influences of P atoms in the backbone and the extent of surface oxidation on the catalytic activity was reported to address the structure−catalytic activity relationship in the ODHP reaction. The calculations show that (1) the P element in BP may influence the composition of the occupied states of BP (P, 47.3%; O, 98.8%; and N, 81.7%) and bring significant impact on its properties. The influence of O in the B 2 O 3 (O) and N in the h-BN (N) was also analyzed for comparison. (2) The more oxidized surface (BP-H) is more reactive than the less oxidized surface (BP-L) in view of the lower free-energy barrier to the rate-determining step (45.8 vs 57.3 kcal/mol for the dehydrogenation of propane step, respectively). This study explains the role of the P element and the effect of surface oxidation and provides a comprehensive understanding of the structure−activity relationship of boron-containing materials in ODHP.

Propane Oxidative Dehydrogenation on Nanosized Boron Carbide: Effect of Boron Content and Its Oxidation Implicated by DFT Calculations

“…The more delocalized nature of the spin density in B 13 C 2 and BP stabilizes the >B–O radical intermediate more than that of h -BN-IM1 , thus with lower reactivity to dehydrogenate propane. This explains the previous findings that in the h -BN system, the dehydrogenation of the h -BN surface to produce BNOH is characterized as the rate-determining step, while in the BP and B 13 C 2 (see later part of this work), the dehydrogenation of the propane is identified as the rate-determining step.…”

“…It merits a discussion on the difference in the spin density distribution in the B 13 C 2 and another two binary boron-containing materials, BP and h -BN, upon the dehydrogenation at their surface >B–OH site. In B 13 C 2 and BP, besides the reactive oxygen species, the spin density may also delocalize to the B sites of the B 13 C 2 cage and the P site of the BP skeleton, while in h -BN, the spin density was confined at the >B–O • site in h -BN-IM1 .…”

“…34 The studies also showed the dependence of mechanism on the composition of the catalyst and identified the rate-determining step being the dehydrogenation of >B−OH groups in the ODH catalyzed by h-BN 30,31,35 while being the activation of propane in the ODH catalyzed by supported boron oxide and boron phosphide. 36,37 In the study of BP-catalyzed ODHP, higher oxidation extent of BP surface, i.e., higher coverage of hydroxyl groups, was found to enhance its catalytic activity. The unique ability of the boron-based ODH systems to remarkably suppress deep oxidation of propane was also investigated, which was attributed to two reasons: (1) the rich presence of boron peroxo, a mild oxidant, enhances the selectivity for the dehydrogenation of 2 o -H over 1 o -H, resulting in a higher yield of iso-propyl radical than n-propyl intermediate.…”

Nanoengineered Design of inside‐Heating Hot Nanoreactor Surrounded by Cool Environment for Selective Hydrogenations

“…[52] The method used was similar to the previously reported work. [53] The B3LYP functional theory was employed to obtain the stationary points. [54][55][56] For the H, C, O, and S atoms, the 6-31G(d,p) basis set was employed, while the LANL2DZ basis set was used for the Pt atom.…”