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The trip to Cancun was a bit longer for some Mexican scientists than for others. Mayela García-Sánchez traveled from the Netherlands, where she is a Ph.D. student at Eindhoven University of Technology's Schuit Institute of Catalysis, working with professor Rutger A. van Santen and senior research scientists Emiel J. M. Hensen and Pieter C. M. M. Magusin. García-Sánchez presented results of experiments aimed at understanding the effects of oxidation and reduction on gallium-containing zeolites. Zeolites loaded with gallium are useful catalysts for converting alkanes to aromatic compounds. Ga/ZSM-5 is used commercially in the Cyclar process developed by BP and UOP, Des Plaines, Ill., for converting liquefied petroleum gas, which is mainly propane and butane, into benzene, toluene, and xylenes. "But the role of gallium in these reactions is still unclear," García-Sánchez noted. To learn about the nature and environment of gallium species in porous materials, García-Sánchez and coworkers used vapor deposition of trimethylgallium to prepare Ga/ZSM-5 specimens. The samples were probed with X-ray absorption spectroscopy, infrared spectroscopy, and other tools, and exposed to oxidizing and reducing conditions. The measurements indicate that gallium bonds as Ga(CH3)2+ in tetrahedral coordination at Brønsted sites in preference to silanol sites. The finding is consistent with computational results, García-Sánchez pointed out. She also observed that reductions proceed faster for tetrahedrally coordinated species than for those with an octahedral geometry and that gallium is more readily dispersed into zeolite micropores upon treatment with hydrogen than oxygen |
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