REDOX PROPERTIES OF MOLTEN-SALTS FOR METHANE ACTIVATION

Molten salt mixtures have been tested in a redox mode as catalysts for the activation of methane at 750-degrees-C. It is found that after pr e-treatment with dioxygen a transition metal halide/sodium vanadate me lt can convert methane selectively to C2+ products in the absence of m olecular oxygen. The melt can be reactivated by passing dioxygen. Elec tron paramagnetic resonance studies of the quenched samples showed tha t the transition metal ions are reduced by methane and can be reoxidis ed by dioxygen. It is also found that higher C2+ selectivity, C2+ yiel d and C2H4/C2H6 ratio are promoted by added transition metal chlorides and, surprisingly, also by the corresponding metal bromides. It suppo rts the suggestion that surface modification by halogen is more import ant than gas radical reactions. Comparison of the molten mixtures unde r redox and cofeed conditions showed that the former gave a higher C2 selectivity, but no oxygenated products whereas formaldehyde was only detected in the cofeed conditions.