Influence of Catalyst Concentration on Activity and Selectivity in Selective Methane Oxidation with Platinum Compounds in Sulfuric Acid and Oleum

Direct catalytic functionalization of methane, a “dream reaction”, is typically characterized by poorly active catalysts and low product selectivity. Selectivity is particularly high for the “Periana system”, in which methane is oxidized to methyl bisulfate in sulfuric acid/oleum using a η2-(2,2′-bipyrimidyl)­dichloroplatinum­(II) ((bpym)­PtCl2, 1) catalyst. Recently it was shown that well-chosen reaction conditions result in not only high selectivity but also remarkably high activity, previously considered to be the prohibiting factor regarding commercialization. The high activity apparently contradicts the original report. Detailed studies of the dependence of activity and selectivity on the catalyst concentration resolve this contradiction and reveal solubility, transformation of catalyst precursors, speciation, and solubility of methane as crucial factors for the observed reaction rates. Additionally, the selectivity pattern clearly discloses the consecutive nature of the reaction network.