Effect of Surface Structure of TiO₂ Nanoparticles on CO₂ Adsorption and SO₂ Resistance

The effect of surface structure of TiO 2 nanocrystals on the structure, amount, and strength of adsorbed CO 2 and resistance to SO 2 was investigated using in situ IR spectroscopy and mass spectrometric techniques along with first-principles density functional theory (DFT) calculations. TiO 2 nanoshapes, including rods {(010) + (101) + (001)}, disks {(001) + (101)}, and truncated octahedra {(101) + (001)}, were used to represent different TiO 2 structures. Upon CO 2 adsorption, carboxylates and carbonates (bridged, monodentate) are formed on TiO 2 rods and disks, whereas only bidentate and monodentate carbonates are formed on TiO 2 truncated octahedra. In general, the order of thermal stability of the adsorbed CO 2 species is carboxylates ≈ monodentate carbonates > bridged carbonates > bidentate carbonates ≈ bicarbonates. TiO 2 rods and disks adsorb CO 2 more strongly than TiO 2 truncated octahedra, which is explained by the larger number of low coordinated surface oxygen and oxygen vacancies on the rods and disks than the truncated octahedra. Further IR studies showed that the structure and binding strength of the adsorbed CO 2 species are affected by the presence of SO 2 . Among the three TiO 2 nanoshapes, CO 2 binding strength for truncated octahedra shows the most decrease due to accumulation of sulfates formed during the SO 2 adsorption cycle. The fundamental understanding obtained here on the effects of the surface structure, oxygen vacancies, and SO 2 on the interaction of CO 2 with TiO 2 may provide insights for the design of more efficient and sulfur-resistant TiO 2 -based catalysts involved in CO 2 capture and conversion.