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Platinum Metals Rev., 1998, 42, (3), 98

Direct Methane Oxidation by Platinum Catalyst

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The conversion of natural gases into more useful alcohols is usually achieved by changing the alkane component of the natural gas into a combination of carbon monoxide and hydrogen (synthesis gas) which is then converted into higher order alkanes by the Fischer-Tropsch reaction (1). These processes require a lot of energy, so it would be less costly if the alkane component, usually methane, could be directly converted into alcohols, by selective oxidation; the main difficulty being the low reactivity of the C-H bond. One such method, from Catalytica Advanced Technologies Inc., California, used toxic mercury(II) salts, and resulted in methane being converted into a methanol ester in an approximately 43 per cent yield.

Now, however, the same group has reported the development of a successful, stable platinum catalyst (2). Platinum salts were already known to be more efficient for the oxidation of methane in strong oxidising acids, but were not stable in hot (>100°C) acid. By utilising stabilising ligands, catalysts of greater stability were developed. They found that the addition of a bidiazine ligand to a platinum(II) salt gave high stability to strong acids and oxidising conditions. One of the most effective catalysts was dichloro(η-2-{2,2′-bipyrimidyl})platinum(II), [(bpym)PtCl2]. Three key steps were proposed for the conversion of methane: C-H activation, oxidation and functionalisation.

The present reaction, which takes place at 220°C, converts ∼ 72 per cent of the methane to methyl bisulfate, and is thought to proceed via the formation of a methyl-platinum species. The authors state that the mechanism of the C-H reaction needs more investigation as the factors controlling its reactivity could lead to greater control of the reaction selectivity.

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References

  1. 1
    R. C. Everson, and D. T. Thompson,, Platinum Metals Rev ., 1981, 25, ( 2 ), 50 ; F. King,, E. Shutt and A. I. Thompson, op. cit ., 1985, 29, ( 4 ), 14
  2. 2
    R. A. Periana,, D. J. Taube,, S. Gamble,, H. Taube,, T. Satoh and H. Fujii, Science, 1998, 280, ( 5363 ), 560

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