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

The effect of surface structure of TiO2 nanocrystals on the structure, amount, and strength of adsorbed CO2 and resistance to SO2 was investigated using in situ IR spectroscopy and mass spectrometric techniques along with first-principles density functional theory (DFT) calculations. TiO2 nanoshapes, including rods {(010) + (101) + (001)}, disks P{(001) + (101)}, and truncated octahedra {(101) + (001)}, were used to represent different TiO2 structures. Upon CO2 adsorption, carboxylates and carbonates (bridged, monodentate) are formed on TiO2 rods and disks, whereas only bidentate and monodentate carbonates are formed on TiO2 truncated octahedra. In general, the order of thermal stability of the adsorbed CO2 species is carboxylates approximate to monodentate carbonates > bridged carbonates > bidentate carbonates approximate to bicarbonates. TiO2 rods and disks adsorb CO2 more strongly than TiO2 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 CO2 species are affected by the presence of SO2. Among the three TiO2 nanoshapes, CO2 binding strength for truncated octahedra shows the most decrease due to accumulation of sulfates formed during the SO2 adsorption cycle. The fundamental understanding obtained here on the effects of the surface structure, oxygen vacancies, and SO2 on the interaction of CO, with TiO2 may provide insights for the design of more efficient and sulfur-resistant TiO2-based catalysts involved in CO2 capture and conversion.