A Mercury-Catalyzed, High-Yield System for the Oxidation of Methane to Methanol

Abstract

A homogeneous system for the selective, catalytic oxidation of methane to methanol via methyl bisulfate is reported. The net reaction catalyzed by mercuric ions, Hg(II), is the oxidation of methane by concentrated sulfuric acid to produce methyl bisulfate, water, and sulfur dioxide. The reaction is efficient. At a methane conversion of 50 percent, 85 percent selectivity to methyl bisulfate ( approximately 43 percent yield; the major side product is carbon dioxide) was achieved at a molar productivity of 10(-7) mole per cubic centimeter per second and Hg(II) turnover frequency of 10(-3) per second. Separate hydrolysis of methyl bisulfate and reoxidation of the sulfur dioxide with air provides a potentially practical scheme for the oxidation of methane to methanol with molecular oxygen. The primary steps of the Hg(II)-catalyzed reaction were individually examined and the essential elements of the mechanism were identified. The Hg(II) ion reacts with methane by an electrophilic displacement mechanism to produce an observable species, CH(3)HgOSO(3)H, 1. Under the reaction conditions, 1 readily decomposes to CH(3)OSO(3)H and the reduced mercurous species, Hg(2)(2+) The catalytic cycle is completed by the reoxidation of Hg(2)(2+) with H(2)SO(4) to regenerate Hg(II) and byproducts SO(2) and H(2)O. Thallium(III), palladium(II), and the cations of platinum and gold also oxidize methane to methyl bisulfate in sulfuric acid.

Direct conversion of methane under nonoxidative conditions

“…Direct conversion of CH 4 with the assistance of oxidants is thermodynamically more favorable than that under nonoxidative conditions. Therefore, the direct conversion of CH 4 under the aid of oxidants has received much more attention than that under nonoxidative conditions, especially when considering the production of fuels and valuable chemicals from CH 4 in order to solve the "oil crisis."…”

“…This presents an entirely different difficulty from what we have become familiar with in petroleum processing, in which the main problem is how to effectively and selectively break the C-C bond. Thermodynamic constraints on the reactions in which all four C-H bonds of CH 4 are totally destroyed, such as CH 4 reforming into synthesis gas or CH 4 decomposition into carbon and hydrogen, are much easier to overcome than the reactions in which only one or two of the C-H bonds are broken under either oxidative or nonoxidative conditions. For this reason, only indirect conversions of CH 4 via synthesis gas into higher hydrocarbons or chemicals are currently available for commercialization.…”

“…For this reason, only indirect conversions of CH 4 via synthesis gas into higher hydrocarbons or chemicals are currently available for commercialization. As for the direct conversion of CH 4 into higher hydrocarbons and/or valuable chemicals, despite enormous efforts conducted via various approaches, such as thermal, homogeneous or heterogeneous catalysis, photocatalysis, and electrocatalysis, profitable and practical applications have not yet been developed.…”

“…Therefore, the direct conversion of CH 4 under the aid of oxidants has received much more attention than that under nonoxidative conditions, especially when considering the production of fuels and valuable chemicals from CH 4 in order to solve the "oil crisis." The study of the oxidative coupling of methane (OCM) was a well-known example that started in the early 1980s and quickly bloomed from the mid-1980s to the mid-1990s [1].…”

Henry Taube: Inorganic Chemist Extraordinaire

“…In his later years in research, he continued to explore coordination chemistry in different guises with an interest in complexes of V II , [164][165][166] substitution and electron transfer in metal complex ion pairs, [167][168][169] and metallocenes. [170][171][172][173][174][175] During this period, he also enjoyed consulting at Catalytica, [176][177][178][179][180][181][182] where he used his knowledge of chemistry to solve practical problems such as the seminal development of catalysts for methane activation. 183 …”