Theoretical models for ?-Al2O3 (110) surface hydroxylation: An ab initio embedded cluster study

Abstract

A theoretical analysis of ␥-Al O 110 surface hydroxylation based on 2 3 ab initio Hartree᎐Fock embedded cluster calculations was carried out. Both tetrahedral and octahedral Al sites were considered. These sites were modeled by a series of clusters of increasing size: Al O , Al O , and Al O , embedded in an array of point charges. 8 3 12 5 16 8The adsorption of water was found to be dissociative or nondissociative depending on the cluster size, although the mechanism clearly converges toward dissociation for the more reliable models in agreement with the experiment. This dependence can be explained in light of the basicity modification of surface oxide ions induced by the environment as well as by surface relaxation. Comparison of chemisorption energies suggests that the preferred site for hydroxylation is a low coordination tetrahedral aluminum.

Study of γ-Alumina Surface Reactivity: Adsorption of Water and Hydrogen Sulfide on Octahedral Aluminum Sites

“…Adsorption energy values derived from theoretical studies vary from -54 35 to -564 kJ/mol. 37 Both results were obtained by quantum chemical methods on clusters that modeled different surface sites. The difference in energy values could be attributed to the cluster model: ref 35 used clusters terminated by hydrogen ions, and the latter ref 37 used clusters embedded in a set of point charges.…”

“…32,33 The reconstruction of the (110) surface 34 was investigated by means of density functional calculations coupled with plane wave basis (DFT-PW). Other works have focused on the reactivity studies of γ-alumina sites in interaction with small molecules such as HCl, 35 CO, 36,8 H 2 O, 8,37 H 2 S, 8 CH 3 OH, 38 MoS 2 , 39 and (Re) 2 (CO) 10 . 40 Under atmospheric conditions, the surface of γ-alumina adsorbs water both molecularly and dissociatively, thus creating hydroxyl groups on the surface.…”

“…Quantum chemical studies were also used in order to investigate the acid−base nature and the local surface structure. , The reconstruction of the (110) surface was investigated by means of density functional calculations coupled with plane wave basis (DFT-PW). Other works have focused on the reactivity studies of γ-alumina sites in interaction with small molecules such as HCl, CO, , H 2 O, , H 2 S, CH 3 OH, MoS 2 , and (Re) 2 (CO) 10 …”

H2dissociation over Ag/Al2O3: the first step in hydrogen assisted selective catalytic reduction of NOx

“…This poses problems for atomistic calculations, and several models have been proposed over the years. [29][30][31][32][33] Here, the spinel structure designed by Digne and co-workers 34 is employed. The g-alumina bulk is optimized using a (4, 2, 2) k-point sampling (4 unique k-points).…”

Small gold species supported on alumina. A computational study of α‐Al2O3(0001) and γ‐Al2O3(001) using an embedded‐cluster approach

“…For γ‐Al 2 O 3 (001), we used a structural model 50, 51 that is based on the P21/m refinement of its bulk structure 52. In contrast to spinel lattices 53–56, no partially occupied positions have been determined in this model of γ‐alumina 50. Surface models based on this refinement have recently been examined to clarify the acidic properties of γ‐alumina 50, 57 and the bonding characteristics of adsorption complexes of small Pd clusters 58–60.…”