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Abstract:
This thesis deals with the selective oxidation of methane to methyl bisulfate, a methanol derivative, in concentrated and fuming sulfuric acid with different catalysts, mostly platinum-based. This system – usually related with the name of Roy A. Periana and Catalytica Inc. – is, due to its high selectivity, a very promising candidate in the field of direct conversion of methane.
Previously invented solid catalysts for this reaction, i.e., Polyacrylonitrile-based nitrogen containing carbon materials, modified with potassium tetrachloroplatinate, were macroscopically customized to be used in a continuous reactor. Subsequent stability tests revealed general problems with carbon corrosion. Furthermore, use of potassium tetrachloroplatinate as catalyst for evaluation of contributions from leached species put question marks on the general understanding of the system.
Following these observations, a comprehensive study towards the fundamentals of the system was undertaken, and the influence of sulfur trioxide, catalyst, and additive concentration on activity, stability, and selectivity of various molecular catalysts was investigated.
Further preliminary studies aimed at a mechanistic understanding. The results point at Pt(IV) to have an active role in this system. Additionally, comparison of several catalytically active elements identifies platinum-based catalysts amongst the best, but iodine-based ones as most promising.
Notably, improved reaction conditions resulted in activities higher than described in catalyst guidelines for viable industrial application. Activity, considered as the biggest issue so far, was shown to be in the range of large scale industrial processes, leaving product separation as the last big problem towards upscaling.
The activities presented in this thesis are, very likely, the highest ever reported for direct oxidation of methane, and several orders of magnitude higher compared to those described in previous reports.
