College Park, Maryland June 6 - 10 , 2004 |
WP10: Oxidation of propane in zeolite Y studied by in situ inelastic neutron scattering
M. Hartl, L.L. Daemen (Los Alamos Neutron Science Center, Los Alamos National Laboratory), J. Eckert (Los Alamos Neutron Science Center, Los Alamos National Laboratory; Materials Research Laboratory, University of California, Santa Barbara), B. Mojet, J. Xu (Department of Chemistry, University of Twente)
Short alkanes, such as propane, are present in natural gas and in volatile petroleum fractions. These molecules can be converted by oxidation into an important feedstock for the production of synthetic materials (plastics) and fine chemicals. Zeolites containing alkaline or alkaline earth cations have been shown to be promising materials (F. Blatter, H. Sun, S. Vasenkov, H. Frei, Catal. Today, 41 (1998) 297) for the oxidation of these small hydrocarbons by low-temperature catalysis in the presence of small oxidant molecules such as O2 . At the present time, however, the interaction between these zeolites and the oxidized reactants has not been studied extensively. Frei and collaborators discussed a possible alkane-oxygen charge transfer state stabilized by the electrostatic field of the cations in the zeolite, but this has not been established.
The electrostatic field inside the pore structure of zeolite Y and the available space for the reactants on the inner surface of the catalyst can be varied by using different cations (Na+ and Ca2+) in zeolite Y with similar ionic radii but different positive charge. Vibrational spectroscopy by incoherent inelastic neutron scattering (IINS), as well as variety of other in-situ techniques, have resulted in an improved understanding of the activation of the reactant molecules and the desorption of the oxidation products. Information on the adsorption sites, surface bonding, and local chemical environment can be inferred from the IINS spectra of the adsorbed molecules. Vibrational spectra of the zeolites NaY, CaY and NaCaY were recorded after their calcination in vacuum, after the adsorption of propane and oxygen inside the zeolite, and after the oxidation of propane by oxygen. Our results combined with IR spectroscopic studies provide useful insights into the sorbate-zeolite host interaction as well as the mechanism of the oxidation reaction, which should lead to the design and development of new catalysts for the selective oxidation of hydrocarbons.
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