The Conversion of Ethylene to Coke on Supported Platinum Catalysts Investigated by 13C Nmr

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Summary

The conversion of ethylene to coke-precursors and coke on Pt/SiO2 catalysts was studied using high-resolution solid state nuclear magnetic resonance (NMR) of carbon-13. The NMR techniques included cross-polarization with magic angle spinning (CP/MAS), CP/MAS with dipolar dephasing, and direct excitation of carbon-13 nuclei. A number of mobile and strongly adsorbed species were identified on Pt/SiO2 samples dosed with labelled ethylene and heated progressively at various temperatures. Highly mobile species observed at various stages of sample treatment include ethylene, ethane, both cis- and trans-but-2-ene, and finally methane. Coke-precursors in the form of strongly adsorbed CnHm fragments and finally coke on the catalyst surface have been observed after treatment at high temperatures. The coke present after treatment at 673 K has been characterized as consisting of aromatic rings with an overall stoichiometry of C2H.

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