Presence of Lithium Ions in MgO Lattice: Surface Characterization by Infrared Spectroscopy and Reactivity towards Oxidative Conversion of Propane

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Trionfetti, Cristiano and Babich, Igor V. and Seshan, K. and Lefferts, Leon (2008) Presence of Lithium Ions in MgO Lattice: Surface Characterization by Infrared Spectroscopy and Reactivity towards Oxidative Conversion of Propane. Langmuir, 24 (15). pp. 8220-8228. ISSN 0743-7463

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Abstract:The surface morphology of Li-promoted MgO catalysts prepared using the sol−gel method (sg) and wet impregnation procedure (imp), respectively, has been studied by low-temperature infrared spectroscopy of adsorbed CO molecules. The results show that step sites, as unselective catalytic centers, are the major features existing on the surface of pure MgO, and those are active toward the oxidative conversion of propane. However, the concentration of these sites is drastically reduced by the incorporation of lithium ions in the MgO lattice. In fact, the incorporated Li+ ions tend to move into the surface region and occupy sites associated with lower coordination number (e.g., step sites). Li/MgO-sg catalysts are characterized by a higher concentration of incorporation of lithium compared to Li/MgO-imp. In the case of oxidative dehydrogenation/cracking of propane, Li/MgO-sg catalysts show higher activity and selectivity to olefins compared to materials prepared using wet impregnation. Catalytic performance differs strongly regarding (i) the amount of olefins formed, and (ii) the ratio of C3H6/C2H4. It is shown that high density of active sites is essential for further oxidative dehydrogenation of propyl radicals to propylene and suppression of cracking reactions pathway.
Item Type:Article
Copyright:© 2008 American Chemical Society
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Science and Technology (TNW)
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Link to this item:http://purl.utwente.nl/publications/59323
Official URL:http://dx.doi.org/10.1021/la8006316
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