Scanning Tunneling Microscopy Evidence for the Dissociation of Carbon Monoxide on Ruthenium Steps

In heterogeneous catalysis, identifying the active site
for key
reaction steps is an important contribution for the optimization of
industrial synthesis. The structure sensitivity of CO dissociation
on a metal catalyst, which is the rate-limiting step for the methanation
and the Fischer–Tropsch processes under certain conditions,
has been debated for years. Here, scanning tunneling microscopy (STM)
and density functional theory (DFT) are used to clarify the role of
monatomic steps in the splitting of CO on a stepped Ru(0 1 54) crystal,
which displays alternating steps with either 4-fold or 3-fold symmetry.
After CO doses at elevated temperatures, the STM images reveal step
decorations characteristic of atomic oxygen resulting from CO dissociation
on every second step. The comparison of the STM images with the results
of DFT calculations shows that the step decoration occurs on the steps
displaying the 4-fold symmetry. We conclude that the active sites
for CO dissociation on ruthenium are located on the 4-fold symmetry
monatomic steps.