Propane oxidative dehydrogenation over highly selective hexagonal boron nitride catalysts: The role of oxidative coupling of methyl

Abstract

Hexagonal boron nitride (h-BN) catalyst has recently been reported to be highly selective in oxidative dehydrogenation of propane (ODHP) for olefin production. In addition to propene, ethylene also forms with much higher overall selectivities to C2-products than to C1-products. In this work, we report that the reaction pathways over the h-BN catalyst are different from the V-based catalysts in ODHP. Oxidative coupling reaction of methyl, an intermediate from the cleavage of C─C bond of propane, contributes to the high selectivities to C2-products, leading to more C2-products than C1-products over the h-BN catalyst. This work not only provides insight into the reaction mechanisms involved in ODHP over the boron-based catalysts but also sheds light on the selective oxidation of alkanes such as direct upgrading of methane via oxidative upgrading to ethylene or CHxOy on boron-based catalysts.

Construction of a Nanoporous Highly Crystalline Hexagonal Boron Nitride from an Amorphous Precursor for Catalytic Dehydrogenation

“…[32][33][34] But the realization of this future economy relies on the development of ah ighly efficient catalytic system for the reversibility and high selectivity of LOHC, [35] especially the N-ethylcarbazole (NEC) and dodecahydro-N-ethylcarbazole (12H-NEC) cycle systems. [34] Considering the highly efficient catalytic activity of h-BN in oxidative dehydrogenation of propane (ODHP) for olefin production, [11,12,37,38] we envisioned that the crystalline nanoporous h-BNNS obtained in this study could act as an efficient metal-free catalyst for the dehydrogenation of 12H-NEC.I ndeed, taking NEC-12H as am odel substrate (Figure 4), a74% yield of NEC was obtained using the as-prepared crystalline h-BNNS as the catalyst at al ow reaction temperature (120 8 8C). [34] Considering the highly efficient catalytic activity of h-BN in oxidative dehydrogenation of propane (ODHP) for olefin production, [11,12,37,38] we envisioned that the crystalline nanoporous h-BNNS obtained in this study could act as an efficient metal-free catalyst for the dehydrogenation of 12H-NEC.I ndeed, taking NEC-12H as am odel substrate (Figure 4), a74% yield of NEC was obtained using the as-prepared crystalline h-BNNS as the catalyst at al ow reaction temperature (120 8 8C).…”

“…[36] However,e ven after decades of research, the unsatisfactory performance obtained using high doses of precious-metal dehydrogenation catalysts and the required high reaction temperatures has proven to be ab ottleneck (Table S1). [34] Considering the highly efficient catalytic activity of h-BN in oxidative dehydrogenation of propane (ODHP) for olefin production, [11,12,37,38] we envisioned that the crystalline nanoporous h-BNNS obtained in this study could act as an efficient metal-free catalyst for the dehydrogenation of 12H-NEC.I ndeed, taking NEC-12H as am odel substrate (Figure 4), a74% yield of NEC was obtained using the as-prepared crystalline h-BNNS as the catalyst at al ow reaction temperature (120 8 8C). Notably,t his yield is much higher than that obtained by the bulk amorphous h-BN (NEC yield:40%), commercialized h-BN (NEC yield:10%)aswell as Pd/C (NEC yield:5 .2 %) under the same conditions.T he enhanced catalytic activity of crystalline h-BNNS is also observed in the dehydrogenation of dodecahydro-N-propylcarbazole (12H-NPC) with ay ield of N-propylcarbazole (NPC) as 63 %(crystalline h-BNNS) and 36 %(amorphous h-BN).…”

Radical Chemistry and Reaction Mechanisms of Propane Oxidative Dehydrogenation over Hexagonal Boron Nitride Catalysts

“…[1a, 5a,c] Interestingly, a recent work implied a possible influence of gas-phase radical chemistry of h-BN catalyst in ODHP reaction, [6] in which no expected relationship was found between the catalytic activity and contact time. Wang et al [7] have proposed that methyl radicals are generated on the h-BN surface from the CÀC bond cleavage, leading to various secondary reaction pathways involving methyl radicals during ODHP. However, to date there is no direct experimental evidence for the presence of radicals in the ODHP reaction over h-BN catalyst, which is possibly due to the high reactivity and short lifetime of the gas-phase radicals.…”

Photoionization Mass Spectrometry for Online Detection of Reactive and Unstable Gas‐Phase Intermediates in Heterogeneous Catalytic Reactions

“…The radicals-involved ODHP reaction mechanism has also been recently proposed over the hexagonal boron nitride (h-BN) catalysts. [92] The generated C 2 and C 1 products showed a higher C 2 /C 1 ratio (> 2) that was different from the case over Vbased catalysts. The authors speculated that the ODHP reactions over the h-BN catalysts initiated with the generation of C 3 H 7 * via the CÀ H bond cleavage of propane, and C 2 H 5 * and CH 3 * radicals via the CÀ C bond cleavage of propane.…”

“…The radicals‐involved ODHP reaction mechanism has also been recently proposed over the hexagonal boron nitride ( h ‐BN) catalysts . The generated C 2 and C 1 products showed a higher C 2 /C 1 ratio (>2) that was different from the case over V‐based catalysts.…”