Distinguishing the roles of anatase TiO2 nanocrystals with {101}, {010} or {001} facets catalyzed O3/H2O2 for low-temperature NO oxidation

To study the crystal facets effects of TiO2 on catalytic O-3/H2O2 for NO oxidation at low temperature, anatase TiO2 nanocrystals with a high percentage of {101}, {010} and {001} facets were prepared by hydrothermal routes without fluorine. The percentages of the {101}, {010} and {001} facets in these three samples were 80%, 70% and 66%, respectively. The sequence of NO oxidation efficiency was determined as TiO2(001) (92%) > TiO2(101) (86%) > TiO2(010) (71%) under the molar ratio of O-3/NO = 0.5 and H2O2/NO = 2.9. The crystal facets mechanism exhibited that TiO2(010) sample had the strongest Lewis acid sites, but TiO2(010) activated H2O2 to produce a stable Ti-OOH, which could not react with O-3 to generate more center dot O-2(-) radicals. TiO2(101) possessed a lower density of five-coordinated Ti atoms (Ti-5c) than TiO2(010) and TiO2(001), the cooperative effect between Ti-5c and H2O2 was the weakest. On the contrary, Ti-OOH on the surface of TiO2(001) was more active for center dot O-2(-) production, meanwhile, TiO2(001) also exhibited the strongest NO adsorption properties. Thus, TiO2(001) had excellent NO oxidation efficiency.