Controlling a spillover pathway with the molecular cork effect

Hydrogenation processes are of paramount importance in the chemical industry with a vast range of applications in the food, petrochemical and pharmaceutical sectors.

Heterogeneous catalysts are widely used for hydrogenation; however, controlling the spillover of hydrogen on catalytic surfaces is challenging.

In a paper published in Nature Materials, Prof. Charles Sykes from Tufts University shows experimentally that it is possible to achieve this type of control on a Pd/Cu(111) catalyst by reversible adsorption of a spectator molecule, CO.  Kinetic Monte Carlo simulations performed by TYC member Dr Michail Stamatakis from the Department of Chemical Engineering at UCL shed light into the molecular-level processes occurring on the catalytic surface, and show that hydrogen can only escape from the catalytic centres (Pd atoms) in the absence of CO. This “molecular cork” effect can have profound implications in catalysis. In particular, it is possible to trap hydrogen on the surface of the catalyst at temperatures higher than the normal desorption temperature of this species from Cu/Pd. Due to the higher temperature, adsorbed hydrogen under these conditions can exhibit high reactivity, thereby increasing the rate of hydrogenation reactions.

Journal link: Nature Materials 12,523–528(2013)doi:10.1038/nmat3620

Figure: These schematics illustrate the effect of CO on either blocking hydrogen uptake or trapping adsorbed hydrogen on the surface above its regular desorption temperature.

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