Understanding nature of active sites required for selective C-O cleavage reactions is critical for creation of high value fuels and chemicals from biomass. A class of catalysts that has demonstrated considerable promise for such transformations are metal particles supported on reducible oxides. This family of catalysts often demonstrate remarkable enhancements in activity and selectivity for selective C-O cleavage reactions that greatly exceeds what would be expected from a physical mixture of the two materials. When the metal and reducible support are combined, it is very challenging to decouple the various potential features that could explain these catalytic activity enhancements. For example, direct interactions with the metal via overcoatings of the support, charge effects induced by the support, and new active sites located at the metal-support interface are challenging to discern from promoter effects where defects are generated on the support via spillover from the metal to carry out selective transformations. In this contribution, we separate these effects by using carbon nanotubes to serve as hydrogen highways to link the metal to the reducible oxide support. We show that hydrogen is readily dissociated on the metal, and it can facilitate the reduction of the oxide on the other end of the nanotube. If spillover is fast enough, one can probe promoter effects independently from those resulting from direct contact between the metal and the oxide support. We use XAS measurements and TPR experiments to confirm the spillover, and probe reactions that are known to occur on exposed Ti cations but not consume them to monitor the presence of defects on the oxide support under steady state conditions. We then show that selective C-O scission reactions involved in the selective deoxygenation of cresol and furfural occur at the perimeter of the metal particle, while other transformations such as those involving methoxy species can be facilitated by promoter effects. <br/>

Use of carbon nanotube hydrogen highways to identify active sites over metals supported on reducible oxides

2019 Spring National Meeting

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