Genesis of Sites for n-Alkane Isomerization

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The proposed research focuses on developing a better understanding of the nature of the active sites on sulfated- and tungstated zirconias for the isomerization of light n-alkanes (n-butane, n-pentane, and n-hexane). To date, zirconia-based catalysts have offered more potential for utilization than has been able to be realized, in large part due to their tendency towards fast deactivation. The reaction induction period, lasting only a few minutes for n-butane isomerization, largely determines the future behavior of sulfated zirconia. The proposed research will make use of an in-situ reaction technique, isotopic transient kinetic analysis (ITKA), to determine the evolution of the concentration and residence time(s) of the surface reaction intermediates during the initial reaction period. Addition of trace amounts of olefins (1-butene, 1-pentene, and 1-hexene) during initial reaction will help to define the nature of the active sites, and in particular "olefin-modified" sites that have recently been identified. In-situ DRIFTS as well as other more traditional ex-situ techniques will be used to characterize adsorbed species and the catalysts studied. The educational component will be the traditional mentoring of graduate and undergraduate students. A better understanding of the similarities and differences of the sites on these catalysts for the isomerization of the different n-alkanes may guide the design of more stable catalysts. Processes built around the use of such solid acid catalysts offer possibilities for replacing less environmentally friendly processes with liquid acids or solid acid catalysts requiring the co-feed of corrosive compounds.