The dehydrative condensation of methanol on zeolites is unique in its ability to form carbon-carbon bonds and concurrently restrict the carbon-chain length based on the shape selective characteristics of the molecular sieve. In the �hydrocarbon pool� mechanism for methanol-to-hydrocarbon (MTH) chemistry, organic species, specifically, olefins and arenes, contained inside the zeolite pore act as scaffolds for C-C bond formation. Therefore, the catalytic behavior in MTH systems is determined not only by the structural and compositional features of the inorganic molecular sieve, but also by the organic co-catalyst that comprises the hydrocarbon pool.Steady state, transient, and isotopically labeled kinetic studies were done to show that the relative contribution of the olefin and arene methylation cycles prevalent in the indirect �hydrocarbon pool� mechanism for MTH conversion over zeolites could be systematically modulated at iso-conversion.  These effects of changing the organic co-catalyst in MTH catalysis persist at varying temperatures, conversion, and space velocity. Therefore, changing the hydrocarbon pool provides a simple and specific strategy to tune selectivity for carbon-carbon bond formation reactions in MTH in a way that can be both predicted and controlled. Kinetic and isotopic studies that probe the identity and reactivity of specific olefin and arene components of the hydrocarbon pool, and an assessment of the relative propagation of olefin and arene methylation cycles as a function of zeolite topology will also be presented.

Controlling selectivity in methanol-to-hydrocarbons catalysis by changing the hydrocarbon pool

243rd National Meeting (2012)

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