Selective Methane Oxidation Catalyzed by Platinum Salts in Oleum at Turnover Frequencies of Large-Scale Industrial Processes

Direct catalytic methane functionalization, a “dream reaction”, is typically characterized by relatively low catalyst activities. This also holds for the η2-(2,2′-bipyrimidyl)­dichloroplatinum­(II) [(bpym)­PtCl2, 1] catalyst which oxidizes methane to methyl bisulfate in sulfuric acid. Nevertheless, it is arguably still one of the best systems for the partial oxidation of methane reported so far. Detailed studies of the dependence of activity on the SO3 concentration and the interplay with the solubility of different platinum compounds revealed potassium tetrachloroplatinate (K2PtCl4) as an extremely active, selective, and stable catalyst, reaching turnover frequencies (TOFs) of more than 25,000 h–1 in 20% oleum with selectivities above 98%. The TOFs are more than 3 orders of magnitude higher compared to the original report on (bpym)­PtCl2 and easily reach or exceed those realized in commercial industrial processes, such as the Cativa process for the carbonylation of methanol. Also space-time-yields are on the order of large-scale commercialized processes.