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Silica-supported tantalum clusters: catalysts for conversion of methane with n-butane to give ethane, propane, and pentanes

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Si02-supported tantalum clusters were prepared by adsorption of the precursor Ta(CH2Ph)5 (Ph is phenyl) on the support followed by treatments in H2 at 523, 623, and 723 K. The resultant clusters, had approximate average diameters of 0.3, 0.8, and 2 nm, as determined by extended X-ray absorption fine structure (EXAFS) spectroscopy. The samples were tested as catalysts for conversion of methane with n-butane in a once-through flow reactor operated at atmospheric pressure and 523 K, and EXAFS spectroscopy was used to characterize the used catalysts. The results show that (a) the catalysts are active for the conversion of methane with n-butane to give ethane, propane, and pentanes; (b) catalytic activity decreased to nearly zero over a time on stream of 22 h; (c) the catalyst incorporating the smallest clusters exhibited the highest initial activity and that incorporating the largest clusters exhibited the lowest activity; (d) each used catalyst contained clusters of approximately the same nuclearity as the respective fresh catalyst, but with Ta–Ta bond lengths approximately 0.17 Å longer than those found in the fresh catalysts. The data are consistent with catalysis by the supported clusters, and the product distributions are consistent with disproportionation of n-butane accompanied by the reaction of methane with propane to give other alkanes.

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Acknowledgments

We thank the National Science Foundation for support (grant CTS-03000982). We acknowledge beam time and the support of the U.S. Department of Energy for its role in the operation of beam line X-18B at the National Synchrotron light Source. We also acknowledge the Stanford Syricluotron Radiation Laboratory, operated by Stanford University for the U.S. Department of Energy, Office of Basic Sciences, for access to beam line 2–3. The EXAFS data were analyzed with the software XDAP [3].

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  1. Department of Chemical Engineering and Materials Science, University of California, Davis, CA, 95616, USA

    Sailendra Nemana & Bruce C. Gates

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  1. Sailendra Nemana
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  2. Bruce C. Gates
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Correspondence to Sailendra Nemana.

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Nemana, S., Gates, B.C. Silica-supported tantalum clusters: catalysts for conversion of methane with n-butane to give ethane, propane, and pentanes. Catal Lett 113, 73–81 (2007). https://doi.org/10.1007/s10562-007-9028-6

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