When metals capable of dissociating hydrogen are supported on reducible oxides, a wide variety of possible active sites are generated for catalytic reactions. This is especially true for reactions involving oxygen containing functional groups present in renewable oxygenated hydrocarbons. Metals can facilitate the formation of surface defects and subsurface defects, OH groups, as well as support overcoatings on the metal. Further, these defects may behave differently when near the perimeter of the metal particle, as these interfacial sites may cooperatively activate specific chemical bonds. While many of these features often exist concurrently under reaction conditions, identifying the kinetic relevance of each is quite challenging. Here we discuss an approach to separate the sites resulting from direct interaction from longer range promoter effects through the use of a carbon containing hydrogen bridge. We show that for a variety of reactions involving C-O cleavage of aldehydes, rearrangement of cyclic ethers, dealkylation of methoxy groups, and coupling of carboxylic acids, this approach can be used to identify the kinetic relevance of the various families of active sites. We reveal that, depending on the strength of the C-O bond, direct interaction may be relevant in some transformations, such as the C-O bond cleavage in furfuraldehyde, while simple promoter effects are sufficient to catalyze others. We then show how product selectivity can be tuned in some instances by modifying the nature of the carbon nanotube hydrogen bridge to modify the rate of generation of the various active sites.<br/><br/><br/>

Discriminating the kinetic relevance of promoter effects from direct metal-support interactions through the use of carbon nanotube hydrogen highways

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.