Porous silicon carbide as a support for Mn/Na/W/SiC catalyst in the oxidative coupling of methane

- Calcination in N2 preserves the supports structure better than calcination in air.
- The presence of Na in catalyst promotes SiC oxidation and catalyst sintering.
- CH4 conversion and C2 yield scale roughly linear with the specific surface area.
- SiC as a support shows a higher CH4 conversion and C2 yield per m2 of surface area than SiO2.

Efficient conversion of methane to higher hydrocarbons via oxidative coupling of methane “OCM” is one of the dream reactions in heterogeneous catalysis. Promising yields of C2 hydrocarbons were reported for nanostructured catalysts based on Mn/Na/W-SiO2. However, the exact role of the nanostructure could not be studied so far due to collapse of the pore structure of the SiO2 support at typical OCM temperatures. We investigate porous SiC as an alternative catalyst support for OCM catalysis. Mn/Na/W/SiC catalysts with different pore size were synthesized via impregnation, calcined under different atmospheres and then studied in OCM. The calcination critically impacts the pore structure and surface area of the obtained catalysts. Calcination in nitrogen preserves the support's structure significantly better than calcination in air. However, the nitrogen-calcined catalysts show a strong loss of porosity during OCM testing. The loss of porosity is caused by the presence of Na, which induces a melting of the surface layer that typically protects SiC against bulk oxidation. OCM tests suggest that the activity and C2 yield of Mn/Na/W/SiC catalysts depend critically on the supports stability, i.e. the surface area retained under reaction conditions.

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