Promotional
Effect of Carbon on Fe Catalysts for Ammonia
Decomposition: A Density Functional Theory Study
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Abstract
Density functional theory calculations
have been performed to investigate
the recombinative desorption of N on terraced Fe(100) and Fe(110)
as well as stepped Fe(111) and Fe(211) surfaces. The results showed
that the stepped surfaces, especially the Fe(111) surface, are more
active than the terraced surfaces, which could be related to the presence
of so-called C<sub>7</sub> sites for the stepped surfaces. Carbon
atoms were found to stabilize the thermodynamically unstable stepped
surfaces to be the energetically favored facets and thus facilitate
the preferential exposure. As these carbon atoms incorporated into
the stepped surfaces in the form of surface or subsurface carbon,
the activation energy for the recombinative desorption of N was lowered,
which was mainly ascribed to the decrease in the d band center of
surface Fe atoms. In addition, a relation between the electronic and
structural properties of Fe catalysts in the absence or presence of
carbon and ammonia decomposition activity was also correlated