Recovery of bromine from methyl bromide using amorphous MnO_x photocatalysts

Amorphous MnO_x (AMO) has been prepared by the reaction of potassium permanganate and oxalic acid. Surface area measurements and pore size distribution analyses show that AMO has high surface (200 m²/g) area and a microporus structure. Kinetic results indicate that methyl bromide degradation using AMO photocatalysts is due to a combination of thermocatalytic and photocatalytic reactions; however, the photocatalytic reaction is predominant. Detailed studies show that both molecular oxygen and bulk lattice oxygen of AMO can be involved in the oxidation of methyl bromide to carbon dioxide. Kinetic data, Auger analyses, and FTIR spectra suggest that both oxidation state changes of Mn and the presence of bromide adsorbed on the surface might lead to deactivation of the catalyst. According to mass balance calculations and analyses with potassium iodide solutions with starch, the final products are bromine, carbon dioxide, and water. The overall reaction for methyl bromide degradation under illumination using AMO photocatalyst can be expressed as CH₃Br_(g) + 7/4 O_2(g) → CO_2(g) + 3/2 H₂O_(g) + 1/2 Br_2(g).