(526a) Methane Pyrolysis with a Molten Cu-Bi Alloy Catalyst

Current methods of hydrogen production from methane generate more than 5 kilograms of CO₂ for every kilogram of hydrogen. Methane pyrolysis on conventional solid heterogeneous catalysts produces hydrogen without CO₂ but the carbon coproduct poisons the catalyst. This can be avoided by using a molten metal alloy catalyst. We present here a study of methane pyrolysis on mixtures of molten Cu-Bi alloys as the catalyst. We find that molten Cu-Bi is an active catalyst, even though pure molten Bi or Cu are not. Surface tension measurements and constant temperature ab initio molecular dynamics simulations indicate that the surface is enriched in Bi and that the catalytic activity is correlated with the concentration of Bi at the surface. Bader charge analysis indicates that bismuth donates charge to copper and the most stable configurations of dissociated methane on these liquid surfaces are those with CH₃ coordinated to the bismuth surface atoms and H coordinated to Cu. Methane-activation energy barriers were calculated using the nudged elastic band (NEB) method to be 2.6 eV and 2.5 eV, on different sites on the Cu₄₅Bi₅₅ alloy. The computed barriers are in agreement with the experimentally measured apparent activation energy of 2.2 ± 0.2 eV.