Final Report Summary - NANOCAT (Catalysis at the Nanoscale)
The ERC project aimed at the investigation of catalysis at the nanoscale. In conventional chemistry, catalytic reactions are studied at the ensemble level, i.e. millions of reacting molecules are monitored at the same time, and when a spectrum (e.g. NMR, MS) is recorded of a reaction mixture it will represent an averaged measurement. This can however obscure the observation of possible differences in reactivity of individual molecules, as well as reaction mechanisms at that scale. In this project we make use of a completely novel method to study reaction mechanisms at the single molecule scale: scanning tunneling microscopy (STM) at a solid/liquid interface. To this end a layer of catalytically active molecules was deposited on a conductive surface, which is subsequently scanned by an atomically sharp needle that does not touch the surface. When a voltage is applied between the surface and the needle, a so-called tunneling current can start to run between them, and since >95 of this current travels through the final atom of the tip, the surface (and the molecules adsorbed on it) can be imaged with atomic resolution. In addition, since the technique relies on tunneling currents, it is extremely sensitive to changes in electronic state of the surface, which enables imaging changes in electronic properties of molecules, e.g. changes in redox state.
We aimed at investigating all aspects of catalysis at the nanoscale: the influence of catalyst ordering on a surface on their catalytic performance, the influence of the surface and the liquid, the effect of chiral surfaces, obtaining electrochemical control over catalysis, and investigation of the mechanisms of substrate selectivity in catalysis. The main outcome of the project involved the investigation of catalytic metal-complexes at a solid/liquid interface. We were able to image these catalytically active molecules at near-atomic resolution and by controlling the voltage between tip and surface, we were able to activate these molecules for the binding of oxygen (O2). We observed at the single molecule level oxygen-oxygen atom dissociation, followed by cooperative binding of single oxgen atoms to adjacent metal-complexes. These oxygen-containing complexes could then react further with molecules from the solution. All the different species could be detected and identiefied with STM due to their differences in appearance in the STM images. Their formation and conversion could be monitored in real-time, and in this way reaction rates, cooperativity effects, and other aspects of the reaction mechanism could be elucidated at the single molecules scale and in the most direct and appealing way: by visualization.
We aimed at investigating all aspects of catalysis at the nanoscale: the influence of catalyst ordering on a surface on their catalytic performance, the influence of the surface and the liquid, the effect of chiral surfaces, obtaining electrochemical control over catalysis, and investigation of the mechanisms of substrate selectivity in catalysis. The main outcome of the project involved the investigation of catalytic metal-complexes at a solid/liquid interface. We were able to image these catalytically active molecules at near-atomic resolution and by controlling the voltage between tip and surface, we were able to activate these molecules for the binding of oxygen (O2). We observed at the single molecule level oxygen-oxygen atom dissociation, followed by cooperative binding of single oxgen atoms to adjacent metal-complexes. These oxygen-containing complexes could then react further with molecules from the solution. All the different species could be detected and identiefied with STM due to their differences in appearance in the STM images. Their formation and conversion could be monitored in real-time, and in this way reaction rates, cooperativity effects, and other aspects of the reaction mechanism could be elucidated at the single molecules scale and in the most direct and appealing way: by visualization.