Bifunctional Catalysts Containing Sites of Controlled Accessibility

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ABSTRACT CTS-9629963 This is an exploration of a novel concept of catalyst design intended to improve selectivity in bifunctional catalysts. The proposed catalysts contain two types of active sites: one type that is in contact with all molecules in the fluid (gas or liquid) medium, and another type, typically metal clusters, effectively inaccessible to most reactants but reachable by small molecules such as hydrogen. This situation should minimize undesired reactions such as metal-catalyzed carbon-carbon bond fission. The restricted accessibility of the metal clusters is achieved by depositing them in a zeolite with one-dimensional micropores that are filled with a physisorbed vapor; it is desired to obtain steady-state conditions characteristic of single-file diffusion. The physisorbed molecules may be converted to carbonaceous materials which would more thoroughly isolate the metal clusters from large molecules while leaving largely unchanged their ability to dissociate hydrogen. The hydrogen atoms can then migrate over the zeolite surface to the more accessible site ("spillover"). This approach if successful would have application to many existing and potential industrial processes, including production of aldehydes from carboxylic acids, ethers from esters, and nitroso compounds from nitro compounds. It could also have utility for enantioselective hydrogenation or hydroformylation. These processes are of great economic importance to the chemical, drug, cosmetic, and agrochemical industries.