Low Temperature Direct Conversion of Methane using a Solid Superacid

摘要

The direct conversion of methane to higher hydrocarbons and hydrogen can be catalyzed using "superacids": nCH(4)- CnHm+xH(2). 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 similar to 1 % at 300 degrees C using ABZ-5. By comparison with SZ, 350 degrees 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 degrees C include both C-2-C-6 hydrocarbons and aromatics.