Coupling of Methane with Li/MgO-Catalysts


Arndt S., Laugel G., Simon U., Heitz S., Otremba T., AKSU Y., ...More

14th Nordic Symposium on Catalysis, Marienlyst, Denmark, 29 - 31 August 2010, pp.70

  • Publication Type: Conference Paper / Full Text
  • City: Marienlyst
  • Country: Denmark
  • Page Numbers: pp.70
  • Akdeniz University Affiliated: Yes

Abstract

The main component of natural gas is methane; its known resources are larger than those of crude oil.
There is a big economical interest in the oxidative coupling of methane, which allows the coupling of
methane to ethane or ethylene.
CH4 + ½ or 1 O2 → C2H4 or C2H6 + H2O
Making this reaction economically feasible, would allocate methane as carbon source for the chemical
industry and solve most of the transport problems of natural gas. However, this reaction has not reached
the commercial stage yet, due to a lack of suitable catalysts. One of the most investigated catalysts is
Li/MgO, first described by Lunsford et al. [1]. Li/MgO is not only an active catalyst, but also suitable
for quantum chemical calculations and surface science experiments, which enables further optimization
of this catalyst. This is not the case for many other catalysts. Despite the intensive research, there are
still many open questions, which need to be answered. Lunsford et al. proposed [Li+O-] centers as active
center [1, 2], but experimental results of Mirodatos et al. did not fully agree with this [3]. This
contradiction has not been solved yet. Some researchers report their catalyst to be stable, others describe
sever deactivations. In some cases, the addition of CO2 was reported to avoid or even reverse the
deactivation [4].
We prepared Li/MgO via different preparative routes (single source precursors, solid state chemistry,
and wet impregnation techniques). A strong scattering of the catalytic results was observed. A
correlation between catalytic performance and preparation and characterisation results, respectively, was
not found. Mirodatos et al. observed a loss of Li in his deactivation experiments [3], we extended the
duration of these experiments and found that after several days time on stream, the activity of Li/MgO
approached the activity and selectivity of pure MgO. The results of our stability experiments indicate,
that a high initial activity is a “suicidal activities” for Li/MgO, because at high conversions, the partial
pressure of H2O is high, above a lethal partial pressure of H2O and the catalyst deactivates. Li/MgOs
with a low initial activity did not show signs of severe deactivation.
References
[1] T. Ito and J.H. Lunsford, Nature 314, 721 (1985).
[2] T. Ito, J.X. Wang, C.H. Lin and J.H. Lunsford, J. Am. Chem. Soc. 107, 5062 (1985).
[3] C. Mirodatos, V. Perrichon, M.C. Durupty and P. Moral, Stud. Surf. Sci. Catal. 34, 183 (1987).
[4] S.J. Korf, J.A. Roos, N.A. de Brujin, J.G. van Ommen and J.R.H. Ross, J. Chem. Soc., Chem.
Commun. 1433 (1987)