In situ solid-state nuclear magnetic resonance studies of reactions in zeolite catalysts

In situ solid-state NMR with magic-angle spinning (MAS) has been used to study reactions on zeolite catalysts. Several new experimental techniques have been developed that enable catalyst samples to be prepared for MAS NMR study without exposure to air or moisture. The design and use of a second-generation CAVERN apparatus that is easily fabricated from glass and other inexpensive materials is described. Two additional CAVERN apparatuses that permit shallow bed adsorption of reactants are also presented.; One of the most successful routes to synthetic fuels is the conversion of methanol to gasoline (MTG) using zeolite catalyst HZSM-5. Despite extensive study, the reaction mechanism for this process is still unresolved. By using in situ MAS NMR, it was possible to identify ethylene and methyl ethyl ether as intermediates in the reaction. It was also possible to demonstrate that CO is neither a catalyst nor an intermediate, as was previously proposed.; Trimethyloxonium, trimethylsulfonium, and trimethylselenonium ions formed on HZSM-5 by adsorption of the corresponding dimethyl chalcogenide. Unlike trialkyloxonium ions, trialkylsulfonium and trialkylselenonium ions were stable at high temperatures and in the presence of alcohols. Trialkylsulfonium and trialkylselenonium ions poisoned the catalyst for MTG chemistry by quantitatively titrating the Bronsted acid sites.; The chemistry of ethylene glycol, ethylene oxide, acetaldehyde, methyl formate, and acetic acid on zeolite catalysts HZSM-5 and CsHX was studied to investigate the use of solid catalysts for fine chemical synthesis. Ethylene oxide and ethylene glycol formed 1,4-dioxane on HZSM-5. All compounds produced hydrocarbons and CO as products at high temperatures. In another study, {dollar}sp{lcub}13{rcub}{dollar}C label exchange between the 1 and 3 positions of allyl alcohol at high temperatures on CsHX zeolite demonstrated the formation of an allyl cation.; Organic synthetic reactions in zeolites can be tuned to give different products in a predictable manner by coadsorption of other reagents. For example, without coadsorbates acetaldehyde formed a mixture of products in HZSM-5. When water was coadsorbed, crotonaldehyde was selectively formed, and when both water and oxygen were present, the acetaldehyde was oxidized to acetic acid. Acetonitrile was converted to either acetamide or acetic acid in zeolite HZSM-5, depending on the quantity of water present.