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Atomic-Resolution in Situ Transmission Electron Microscopy of a Promoter of a Heterogeneous Catalyst
Thomas W. Hansen,1Jakob B. Wagner,12Poul L. Hansen,1Søren Dahl,1Haldor Topsøe,1Claus J. H. Jacobsen1*
Insight into the location, state, and function of a promoter in
heterogeneous catalysis was obtained through atomic-resolutionin situ
transmission electron microscopy. In the most active rutheniumcatalyst
for ammonia synthesis known so far, the barium promoteris shown to be
located in two different phases in the catalyst.The increased activity
is suggested to be related to a two-dimensionalbarium-oxygen overlayer
on the ruthenium crystals. The possibilityfor conducting such studies
for other reactions could add substantiallyto our current
understanding of heterogeneous catalysis. Heterogeneouscatalysis plays
an increasingly important role in environmentalprotection processes,
in fuel upgrading, and in providing themajority of the chemical
building blocks required by contemporarysociety. Most heterogeneous
catalysts of industrial importanceare multicomponent materials that
are designed by trial-and-errorexperimentation. Application of even
the most sophisticated physical-chemicalcharacterization techniques is
usually not sufficient to obtaina complete understanding of the
structure of the active site,the reaction mechanism and kinetics, the
structural dynamics,and the specific roles of all catalyst components.
1 Haldor Topsøe A/S, Nymøllevej 55, DK-2800
Lyngby, Denmark.
2 Niels Bohr Institute for
Astronomy, Physics, and Geophysics, University of Copenhagen,
Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
*
To whom correspondence should be addressed. E-mail:
chj{at}topsoe.dk
