Tracking Rh Atoms in Zeolite HY: First Steps of Metal
Cluster Formation and Influence of Metal Nuclearity on Catalysis of
Ethylene Hydrogenation and Ethylene Dimerization
The
initial steps of rhodium cluster formation from zeolite-supported
mononuclear Rh(C<sub>2</sub>H<sub>4</sub>)<sub>2</sub> complexes in
H<sub>2</sub> at 373 K and 1 bar were investigated by infrared and
extended X-ray absorption fine structure spectroscopies and scanning
transmission electron microscopy (STEM). The data show that ethylene
ligands on the rhodium react with H<sub>2</sub> to give supported
rhodium hydrides and trigger the formation of rhodium clusters. STEM
provided the first images of the smallest rhodium clusters (Rh<sub>2</sub>) and their further conversion into larger clusters. The samples
were investigated in a plug-flow reactor as catalysts for the conversion
of ethylene + H<sub>2</sub> in a molar ratio of 4:1 at 1 bar and 298
K, with the results showing how the changes in catalyst structure
affect the activity and selectivity; the rhodium clusters are more
active for hydrogenation of ethylene than the single-site complexes,
which are more selective for dimerization of ethylene to give butenes
