Density functional theory (DFT) and coupled cluster theory (CCSD(T)) were used to study the addition of CO to group 4 (MO) and group 6 (MO) (n = 1, 2, 3) nanoclusters. The structures and energetics arising from Lewis acid-base addition (physisorption) and formation of CO (chemisorption) of CO to these clusters were predicted. Physisorption and chemisorption of CO are predicted to be thermodynamically allowed for group 4 (MO) clusters, with chemisorption being more favored energetically. Correlations of the ligand binding energies (LBEs) for the group 4 clusters are made with the fluoride affinities and M-O and M═O bond strengths of the clusters. The LBEs for chemisorption on the Zr and Ti clusters are consistent with published experimental and computational studies of bulk solids. Physisorption LBEs for the Ti and Zr clusters are more exothermic than the bulk values, as the cluster models allow for better relaxation at the metal sites. Chemisorption is not predicted to occur with group 6 (MO) clusters, as the larger chemisorbed structures were all found to be metastable. CO is predicted to weakly physisorb to (WO) with physisorption correlating with the Lewis acidity of the metal site.

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The addition of NO 2 to Group IV (MO 2 ) n and Group VI (MO 3 ) n (n = 1−3) nanoclusters was studied using both density functional theory (DFT) and coupled cluster theory (CCSD(T)). The structures and overall binding energetics were predicted for Lewis acid−base addition without transfer of spin (a physisorption-type process) and the formation of either cluster-ONO (HONO-like or bidentate bonding) or NO 3− formation where for both the spin is transferred to the metal oxide clusters (a chemisorption-type process). Only chemisorption of NO 2 is predicted to be thermodynamically allowed at temperatures ≥298 K for Group IV (MO 2 ) n clusters with the formation of surface chemisorbed NO 2 being by far the most energetically favorable. The ligand binding energies (LBEs) for physisorption and chemisorption on the TiO 2 nanoclusters are consistent with computational studies of the bulk solids. Chemisorption is only predicted to occur for (CrO 3 ) n clusters in the form of a terminal nitrate containing species whereas the larger chemisorbed nitrate structures for (MoO 3 ) n and (WO 3 ) n were found to be metastable and unlikely to form in any appreciable amount at temperatures of 298 K and higher. NO 2 is predicted to only be capable of physisorbing to (MoO 3 ) n and (WO 3 ) n at lower temperatures and therefore unlikely to bind NO 2 at temperatures ≥298 K. Correlations between the (MO 3 ) n NO 2 ligand bond energies and the chemical properties of the parent (MO 3 ) n clusters (Lewis acidity, ionization potentials, excitation energies, and M = O/M−O bond strengths) are described.

Adsorption of CO to uranium oxide, (UO), clusters was modeled using density functional theory (DFT) and coupled cluster theory (CCSD(T)). Geometries and reaction energies were predicted for carbonate formation (chemisorption) and Lewis acid-base addition of CO (physisorption) to these (UO) clusters. Chemisorption of multiple CO moieties was also modeled for dimer and trimer clusters. Physisorption and chemisorption were both predicted to be thermodynamically allowed for (UO) clusters, with chemisorption being more thermodynamically favorable than physisorption. The most energetically favored (UO)(CO) clusters contain tridentate carbonates, which is consistent with solid-state and solution structures for uranyl carbonates. The calculations show that CO exposure is likely to convert (UO) to uranyl carbonates.

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