Using DFT calculations and acetamide as the main example,
we show
that ceria is a potential catalyst for the hydrolysis of amide and
similar bonds. The overall reaction is endergonic in the gas phase,
yielding acetic acid and ammonia, but is slightly exergonic in the
aqueous phase, which facilitates ionization of the products (CH
3
COO
–
and NH
4
+
). Neighboring
Ce and O sites on the CeO
2
(111), (110), and (100) facets
are conducive to the formation of an activated metastable tetrahedral
intermediate (TI) complex, followed by C–N bond scission. With
van der Waals and solvation effects taken into account, the overall
reaction energetics is found to be most favorable on the (111) facet
as desorption of acetic acid is much more uphill energetically on
(110) and (100). We further suggest that the Ce–O–Ce
sites on ceria surfaces can activate X(=Y)–Z type bonds
in amides, amidines, and carboxylate and phosphate esters, among many
others that we term “generalized esters”. A Brønsted-Evans–Polanyi
relationship is identified correlating the stability of the transition
and final states of the X–Z generalized ester bond scission.
A simple descriptor (ΣΔχ) based on the electronegativity
of the atoms that constitute the bond (X, Y, Z) versus those of the
catalytic site (O, Ce, Ce) captures the trend in the stability of
the transition state of generalized ester bond scission and suggests
a direction for modifying ceria for targeting specific organic substrates.