Low Temperature Direct Conversion of Methane using a Solid Superacid

Abstract

The direct conversion of methane to higher hydrocarbons and hydrogen can be catalyzed using "superacids": nCH 4 !C n H m + xH 2 . The first report of catalytic oligomerization of methane using superacids was that of Olah et al., who demonstrated the superacidity of FSO 3 HÀSbF 5 , which is a liquid. More recently, Vasireddy et al. showed that gas-phase HBr/AlBr 3 was an active superacid. The only reported solid superacid for methane oligomerization is sulfated zirconia (SZ). Here, we report a new class of Br-based solid superacids, AlBr x /H-ZSM-5 ("ABZ-5", x = 1 or 2). ABZ-5 is based on gas-phase HBr/AlBr 3 , with the objective of synthesizing a heterogeneous analogue of the gas-phase superacid HBr/AlBr 3 . The results show that ABZ-5 is significantly more active than SZ. Perhaps more significantly, results here show methane conversions of~1 % at 300 8C using ABZ-5. By comparison with SZ, 350 8C is the lowest temperature reported in the literature at which measurable conversions are shown, and the corresponding methane conversions were < 0.15. Here, we demonstrate direct conversion of methane using a solid superacid catalyst, AlBr x /H-ZSM-5. This solid catalyst is synthesized using a vapor-phase process in which AlBr 3 vapor is grafted on to solid H-SZM-5. This catalyst is characterized using NH 3 -TPD, XRD, and DRIFTS. Hydrocarbon products observed in the temperature range of 200-400 8C include both C 2 -C 6 hydrocarbons and aromatics.[a] S.

Single Ru Sites-Embedded Rutile TiO2 Catalyst for Non-Oxidative Direct Conversion of Methane: A First-Principles Study

“…The innovation in reaction process by adding suitable oxidants (such as H 2 O 2 , N 2 O, etc.) or superacid can significantly improve the thermochemistry and reduce the reaction temperatures for direct methane conversion. − The electrocatalytic conversion of methane, which can operate at milder conditions and avoid additional separation of products (H 2 from C 2 H 4 ), also provides a more economical and eco-friendly approach for the direct methane conversion …”

Zeolite-based catalysts for oxidative upgrading of methane: design and control of active sites

“…16 In contrast, at 698 K, the oxidation of methane and produced hydrocarbons proceeded readily to form CO and CO 2 . In a related study by Spivey et al, the surface of H-MFI (i.e., H-ZSM-5) was modified by HBr + AlBr 3 , a combination known to be a superacid, 19 and the resulting catalyst converted methane into C2, C3, C4, and aromatic compounds in the absence of an oxidant at 573 K. 20 However, the methane conversion was only ∼1%. These reports suggest that the activation of methane remains a great challenge even with state-of-the-art zeolite-based superacid catalysts, owing to the almost inert nature of methane against acid-base reactions.…”

Mukaiyama Award: M. D. Burke und S. Matsunaga / Ryoji Noyori Prize and Paracelsus Prize: S. E. Denmark / Henry J. Albert Award: M. P. Doyle / ORCS Awards: P. Chirik und J. J. Spivey / FNP Award: M. Drąg

“…The Spivey group develops thermally stable catalysts that resist carbon deposition for dry reforming and bi‐reforming of methane, and they design a simplified process for the carboxylation of methane to acetic acid and subsequent reaction with ethylene/oxygen to vinyl acetate. In a Full Paper in ChemCatChem they recently described direct methane conversion at low temperatures using a solid superacid …”