Low Temperature Direct Conversion of Methane using a Solid Superacid

Document Type

Article

Publication Date

11-7-2018

Abstract

The direct conversion of methane to higher hydrocarbons and hydrogen can be catalyzed using “superacids”: nCH4→CnHm+xH2. The first report of catalytic oligomerization of methane using superacids was that of Olah et al., who demonstrated the superacidity of FSO3H−SbF5, which is a liquid. More recently, Vasireddy et al. showed that gas-phase HBr/AlBr3 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, AlBrx/H-ZSM-5 (“ABZ-5”, x=1 or 2). ABZ-5 is based on gas-phase HBr/AlBr3, with the objective of synthesizing a heterogeneous analogue of the gas-phase superacid HBr/AlBr3. The results show that ABZ-5 is significantly more active than SZ. Perhaps more significantly, results here show methane conversions of ∼1 % at 300 °C using ABZ-5. By comparison with SZ, 350 °C 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, AlBrx/H-ZSM-5. This solid catalyst is synthesized using a vapor-phase process in which AlBr3 vapor is grafted on to solid H-SZM-5. This catalyst is characterized using NH3-TPD, XRD, and DRIFTS. Hydrocarbon products observed in the temperature range of 200–400 °C include both C2–C6 hydrocarbons and aromatics.

Publication Source (Journal or Book title)

ChemCatChem

First Page

5033

Last Page

5038

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