Effect of Surface Structure of TiO<sub>2</sub> Nanoparticles\non CO<sub>2</sub> Adsorption and SO<sub>2</sub> Resistance

The\neffect of surface structure of TiO₂ nanocrystals\non the structure, amount, and strength of adsorbed CO₂ and\nresistance to SO₂ was investigated using in situ IR spectroscopy\nand mass spectrometric techniques along with first-principles density\nfunctional theory (DFT) calculations. TiO₂ nanoshapes,\nincluding rods {(010) + (101) + (001)}, disks {(001) + (101)}, and\ntruncated octahedra {(101) + (001)}, were used to represent different\nTiO₂ structures. Upon CO₂ adsorption, carboxylates\nand carbonates (bridged, monodentate) are formed on TiO₂ rods and disks, whereas only bidentate and monodentate carbonates\nare formed on TiO₂ truncated octahedra. In general, the\norder of thermal stability of the adsorbed CO₂ species\nis carboxylates ≈ monodentate carbonates > bridged carbonates\n> bidentate carbonates ≈ bicarbonates. TiO₂ rods\nand disks adsorb CO₂ more strongly than TiO₂ truncated octahedra, which is explained by the larger number of\nlow coordinated surface oxygen and oxygen vacancies on the rods and\ndisks than the truncated octahedra. Further IR studies showed that\nthe structure and binding strength of the adsorbed CO₂ species\nare affected by the presence of SO₂. Among the three TiO₂ nanoshapes, CO₂ binding strength for truncated\noctahedra shows the most decrease due to accumulation of sulfates\nformed during the SO₂ adsorption cycle. The fundamental\nunderstanding obtained here on the effects of the surface structure,\noxygen vacancies, and SO₂ on the interaction of CO₂ with TiO₂ may provide insights for the design\nof more efficient and sulfur-resistant TiO₂-based catalysts\ninvolved in CO₂ capture and conversion.