Methane to Value Added Chemicals Using a Solid Superacid Catalyst

Authors: 
Spivey, J., Louisiana State University
Kanitkar, S., Louisiana State University
Carter, J. H., Cardiff University
Hutchings, G. J., Cardiff Catalysis Institute
Ding, K., Louisiana State University
The shale gas revolution has had a significant impact on the production of natural gas and its conversion into higher-value products. The most commonly practiced methane conversion process involves the use of a co-reactant as an oxidant (typically H2O). Non-oxidative routes involve the use of what is known as a superacid, a compound that has acidity higher than 100% sulfuric acid. A number of superacids are liquids; e.g., HF-SbF51, FSO3H-SbF51. Recently, gas-phase HBr-AlBr32 has shown superacidity for the conversion of methane into value added chemicals, but neither liquid- nor gas-phase superacids can serve as the basis of a practical process because separation of the superacid from the products is unrealistic. The literature has reported attempts to prepare solid superacids using sulfated zirconia3, but both poor yields and rapid deactivation have limited their further use. The challenge here is to show that the superacidity that has been demonstrated in gas-phase catalysts can be shown in a solid.

Here, we propose a new solid catalyst based on AlBr3 supported on zeolites. DRIFTS using pyridine showed presence of an additional Brønsted acid site as compared to the H-ZSM5 base zeolite. NH3-TPD quantitatively confirmed the presence of more acid sites than base zeolite. This increase in acid site density and creation of a superacid site was able to catalyze methane into higher-value added chemicals such as C2-C8hydrocarbons. It appears that the reaction is produced in a step-chain oligo-condensation mechanism. Additional tests on ethane oligomerization showed a similar range of hydrocarbon products, and with a higher TOF, as expected.

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