چکیده :
The activation of highly catalytic c-alumina surfaces by thermal treatment and the description of the
related chemical processes at atomic scale is a topical issue. According to a recent study [J. Am. Chem.
Soc. 134 (2012) 14430], the enhanced reactivity of c-alumina has been associated to tri-coordinated aluminum
sites which supposedly are exposed exclusively on the (110) surfaces of this oxide. In this work,
we explore this possibility by modeling the (100) and (110) terminations using Krokidis et al. [J. Phys.
Chem. B 105 (2001) 5121] bulk structure and performing an extensive search of the most stable hydrated
surface models at conditions consistent with experiment. Among the 156 structures analyzed, we identify
several ‘‘metastable’’ models for the (110) surface with a considerable probability of containing the
AlIII centers at OH coverages of 9.0 and 6.0 then test the reactivity of these sites through their
Lewis acidity by simulating the CO adsorbtion on the surface and our results confirm the high reactivity
of AlIII centers. Based on the Gibbs free energy of the explored structures, we carry on a thermodynamical
analysis at varying hydroxylation degrees and pretreatment temperatures and simulate the experimental
volcano-type behavior reported in [J. Am. Chem. Soc. 134 (2012) 14430] and predict the optimum pretreatment
temperature as 700 C, in very good agreement with experimental findings. We further use
infrared and solid state MAS NMR spectroscopies and reproduce the 1H MAS NMR spectra under high vacuum
conditions (105 Torr). The strong resemblance of spectra to the experimental ones in the literature
[J. Phys. Chem. C 116 (2012) 834] validate further the structural models we have generated in this study.
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