Active sites responsible for the selective conversion of C-O bonds over metals supported on reducible oxides are challenging to identify. When depositing active metals capable of readily dissociating H2 (Pt, Pd, Ni, Ru, etc.) on a reducible oxide support (e.g. TiO2), rates of C-O bond cleavage are often greatly enhanced when compared to other non-reducible supports. While the concept of hydrogen spillover from the metal to the support is a long debated and controversial topic over insulating supports such as SiO2, spillover from a metal to conductive carbon based supports with surface functional groups and reducible oxides is known to occur.1 This makes it highly challenging to differentiate the kinetic relevance of C-O cleavage events that occur at new active sites that are generated which require the reactant to simultaneously interact with the metal and the support from longer range spillover-induced promoter effects. In this contribution, we show how these effects can be systematically decoupled for a variety of C-O cleavage reactions by both systematically varying the metal-support interfacial area as well as the support polymorph, revealing how the cause of enhanced activity of oxygenates is different for different classes of molecules.2,3 We then show how carbon nanotubes can serve as hydrogen highways to decouple the long-range promoter effects from sites located at the metal-support interface,4 using examples of furanic and phenolic aldehydes, ethers and carboxylic acids as examples to illustrate the ability to identify the kinetic relevance of each site under reaction conditions.

Distinguishing the kinetic relevance of sites at a metal-support interface from promoter effects

2019 Fall National Meeting

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