Oxidative Dehydrogenation of Propane over a High Surface Area Boron Nitride Catalyst: Exceptional Selectivity for Olefins at High Conversion

Abstract

Developing environment-friendly active and selective catalysts for oxidative dehydrogenation of propane for on-purpose propene synthesis is challenging despite tremendous industrial potential for this reaction. Herein, we report on catalytic activity of high surface area hexagonal boron nitride, toward oxidative dehydrogenation of propane. It shows remarkable selectivity for alkenes (∼70%) at very high conversion (of ∼50%) of propane. Propene and ethene selectivities as high as 53 and 18%, respectively, were obtained at a conversion of 52%. The catalytic activity is retained continuously for 5 h. Regeneration in ammonia brings back the catalytic activity to its full potential. Oxidation of surface B–N bonds in oxygen leads to the diminishing catalytic activity after 5 h which, on heating in ammonia, reduced back to their native form, regaining the indigenous activity. Remarkably, the addition of ammonia in the reaction feed showed stable activity for more than 100 h.

Why Boron Nitride is such a Selective Catalyst for the Oxidative Dehydrogenation of Propane

“…We point out that both HOOC and > BOC can either propagate upon reaction with propane or terminate (Reactions (6) and (7)). This leads to ahigher radical quasi steadystate concentration-at ag iven conversion-at higher propane concentrations,l eading to the apparent second order observed for propane (Figure 1).…”

“…Thea ctivation energy of this water-mediated surface-regeneration process is compatible with experimentally reported apparent activation energies for hBN-catalyzed ODH in the 200-250 kJ mol À1 range. [6,12,27] Therefore,w eh ypothesize that this water-mediated site regeneration is the rate-limiting reaction in the overall ODH reaction, and not the H abstraction from the alkane substrate as hypothesized for vanadium. [20,28] Summarizing the findings from our computational studies, we identified two radical initiation mechanisms Reactions (2) and (3), and Reaction (4):…”

“…Hexagonal boron nitride (hBN) and other boron-containing materials recently emerged as promising catalysts for the oxidative dehydrogenation (ODH) of small alkanes,w ith unprecedented high olefin selectivity. [1][2][3][4][5][6] Breakthroughs in ODH research could drastically reduce the energy that is required in the synthesis of building block olefins.Ithas been shown that the oxidation of the catalyst surface to an amorphous boron hydroxy oxide layer is crucial for ODH activity,a nd the surface composition of these boron-based materials is highly dynamic and sensitive to the reaction conditions. [7][8][9] As more information is obtained from these complex materials,i ti si mperative to continuously revisit mechanistic hypotheses to support experimental evidence.…”

Progress in the oxidative dehydrogenation of light alkanes to light olefins on metal-free catalysts

“…Su等 [13] 制备了高比表氮化硼纳米片 (BN nanosheets)应用于乙烷氧化脱氢反应中, 得到了 优于商业h-BN的活性和选择性. Eswaramoorthy等 [14] 也报道高比表面的h-BN可以提高丙烷氧化脱氢反应 的性能, 在丙烷的转化率为52%时, 丙烯和乙烯的选择 性分别为53%和18%. 但催化剂只能维持5 h的稳定性, 随后出现失活, 通过加入氨气则可以再生催化剂活性, 并通过氨气共进料可以实现100 h的催化剂稳定性.…”

Synthesis, characterization, and evaluation of high selectivity mixed molybdenum and vanadium oxide catalysts for oxidative dehydrogenation of propane

“…In recent years, considerable research efforts have been focused on the oxidative dehydrogenation of propane to propylene . Propylene is an important chemical feedstock that is in demand mainly for the production of polypropylene, acrylic acid acrylonitrile, and iso‐propanol.…”