Reaction of SO2 with Group IV and VI transition metal oxide clusters

Abstract

The addition of SO2 to the Group IV (MO2)n and VI (MO3)n (n = 1, 2, 3) nanoclusters was studied using density functional theory (DFT) and coupled cluster theory (CCSD(T)). Structures and ligand binding energies were predicted for the Lewis acid-base addition (physisorption), or SO32− or SO42− formation (chemisorption) of SO2 to these clusters. Physisorption is predicted to be thermodynamically allowed for the Mo and W clusters at 298K, and for Cr only at lower temperatures. Chemisorption by SO42− formation is thermodynamically allowed only for Cr clusters due to the higher reducibility of the metal center. Correlations were made between the ligand binding energies (LBEs) of the (MO3)nSO2 clusters and the chemical properties of the parent (MO3)n clusters (Lewis acidity, reducibility, and MO and MO bond strengths). Physisorption and chemisorption by SO32− formation is predicted to be thermodynamically possible for Group IV clusters, and SO4−2 formation is predicted not to occur, suggesting that sulfate formation does not proceed by the direct reaction of a pure metal oxide surface and SO2.