Light olefins such as ethylene and propylene are important feedstocks for the rubber and plastic industry. Typically, light olefins are made by cracking hydrocarbons at high temperatures, > 1000 K. However, this process is unselective and inefficient, producing olefin mixtures and significant amounts of coke byproduct. A key challenge is to develop catalysts that selectively dehydrogenate alkanes, e.g. propane → propene + H2. The hydrogen byproduct can be separated and further used in other industrial processes.
Platinum nanoparticles on oxide supports are promising alkane-dehydrogenation catalysts. Recently, it has been demonstrated that PtGa and PtIn alloys can hinder coke formation, and thereby show better catalyst activity and stability.1 While it is known that Ga and In form bimetallic alloys with Pt, the exact composition and structure of the alloy are unknown. Even more problematic, PtGa catalysts are most active as small clusters ~0.7 nm in diameter, which is roughly 10 atoms. This small cluster size is difficult to control synthetically because of the general tendency of these clusters to agglomerate into larger nanoparticles.
To address these issues, we propose to prepare PtGa and related MM' clusters using a spatially confining zeolite host and preassembled, dinuclear M−M' compounds as the bimetallic precursors. Traditionally, bimetallic alloys are prepared from two discrete mononuclear metal (M and M') precursors. In contrast, we will use dinuclear M−M' precursors to control the metal composition within the cluster and to ensure formation of the MM' interaction. The use of dinuclear units will enable us to target bimetallic MM' clusters of programmable identity (by varying M and M') and size (by varying the number of loading steps into the zeolite host and/or the pore sizes of various zeolite hosts). A second novel aspect of this proposal is the use of hierarchically structured zeolites, which contain both micro- and mesopores: the micropores will stabilize the MM' clusters, while the mesopores allow facile mass transport during the catalytic reaction. Finally, all MM' clusters will be canvassed for activity in various chemical reactions of industrial relevance. At the end of this study, we will be able to determine structure-activity relationships of these new bimetallic materials to guide further catalyst discovery and development.
435 Amundson Hall, 421 Washington Ave. SE, Minneapolis, MN, 55455
P: 612-626-0713 | F: 612-626-7805