Ab initio molecular orbital study of the mechanism of SO2 oxidation catalyzed by carbon

✍ Scribed by Frances H. Yang; Ralph T. Yang

• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 264 KB
• Volume: 41
• Category: Article
• ISSN: 0008-6223
• DOI: 10.1016/s0008-6223(03)00249-5

✦ Synopsis

Ab initio molecular orbital calculations were performed on the possible pathways of the carbon-catalyzed oxidation of SO by O / H O to form sulfuric acid. Both zigzag and armchair edge sites of graphite, with and without surface oxide, were 2 2 2 considered as the possible active sites. For the sites with oxide, both isolated and twin oxides were included. MO calculations at the B3LYP/ 6-31G(d) / / HF / 3-21G(d) level were used for calculating the energies of SO adsorption, 2 oxidation and hydration. Based on these calculations, three viable pathways emerged, and all three took place on the zigzag edge sites. Hence the armchair sites were not viable sites. On the bare surface, the only possible pathway involved the formation of a sulfurous acid intermediate. Thus, SO was first adsorbed on the bare zigzag sites, followed by reaction with 2 H O to form H SO , which was further oxidized by O to form the end product. On the zigzag edge site with isolated oxide, 2 2 3 2 both pathways with either SO or H SO as the intermediate are possible. Chemisorption on the edge sites containing twin 3 2 3

oxides was not viable. This latter result explains the seemingly conflicting results in the literature regarding the dependence of SO adsorption (and oxidation) on the amount of surface oxygen.

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