Methane oxidation to acetic acid catalyzed by Pd 2+ cations in the presence of oxygen

Abstract

Synthesis of acetic acid from methane catalyzed by Pd 2+ cations dissolved in sulfuric acid was investigated to determine the effects of reaction conditions and the mechanism. Acetic acid yield was found to be a strong function of CH 4 and O 2 partial pressures. High O 2/CH 4 ratio and high total pressure delivered the highest yield of acetic acid (14.2 turnovers of Pd 2+) and the highest retention of Pd 2+ in solution (96%). Byproducts were sulfur containing compounds (most notably methyl bisulfate) and CO x , but the acetic acid selectivity was maximized (82%) by lowering the reaction temperature. Methane is activated by Pd(OSO 3H) 2, forming (CH 3)Pd(OSO 3H). CO, generated from the oxidation of methyl bisulfate, inserts into the CH 3 Pd bond creating a (CH 3CO)Pd(OSO 3H) species. Reaction of this complex with H 2SO 4 produces acetic acid. Pd 2+ is reduced to Pd 0 during the oxidation of methyl bisulfate or CO, and Pd 0 is reoxidized to Pd 2+ by H 2SO 4 and O 2.