Well-Defined Catalysts for Hydrocarbon Transformations: Supported Single Atom and Zeolite Catalysis
Abstract: Understanding the structure/property relationships for heterogeneous catalysts is often a difficult task. To that goal, we show examples from three well-defined catalyst systems useful for conversion of hydrocarbon molecules. In the first two examples, we explore the use of supported organo-metallic reagents for the metathetic transformation of butenes to propene and the hydrogenation of arenes to cyclohexanes. In the first example, W-H/Al2O3 was used as a precatalyst to selectively produce propylene from various butene feeds. In the second example, we explore the use of supported organo-zirconium reagents for arene hydrogenation. Competitive hydrogenation of benzene/toluene mixtures shows selectivity varying with catalyst structure.
In the second section, we show that MTW zeolite-based catalysts are attractive for the oligomerization of propene and butenes to gasoline. We use multiple characterization techniques to better understand the catalyst and product properties. Phosphorous treatment of these Al2O3 bound MTW zeolite catalysts allows significant enhancement of the selectivity to gasoline product during oligomerization. Using solid-state NMR techniques, among other characterization methods, we observe that along with conversion of the binding matrix from Al2O3 to alumino-phosphates coating the surface of the MTW zeolite crystals, the interaction of P with zeolite framework Al is a major effect, reducing the acidity of the zeolite and thus affecting the catalytic results. Via this modification, we attain catalytic performance similar to that of a traditional solid phosphoric acid catalyst, but with a significant yield of tri-isobutylenes.