tert-Butanol Chemistry on Rutile TiO2(110): The Effect of Surface Oxidation

We have studied the surface chemistry of tert-butanol ((CH3)(3)COH) on reduced and oxidized rutile (R-) TiO2(110) surfaces using the temperature-programmed desorption (TPD) method. On the reduced R-TiO2(110) surface, (CH3)(3)COH molecules mainly decompose into isobutene (iso-C4H8) and water (H2O) at the oxygen vacancy (O-v) sites at about 440 K, with a small amount of iso-C4H8 formed on the five-coordinated Ti4+ sites (Ti-5c). On the oxidized R-TiO2(110) surfaces, O-v's can be occupied by O-2, thus inhibiting the iso-C4H8 formation channel at the O-v sites. However, a new reaction pathway for iso-C4H8 production occurs on the Ti-5c sites and gradually becomes dominant with increasing O-2 exposure. At 0.5 L O-2 exposure, the yield of iso-C4H8 production is nearly 5 times bigger than that on the reduced surface, illustrating that surface oxidation can enhance iso-C4H8 formation on R-TiO2(110) significantly. In addition, a small amount of (CH3)(3)COH can be detected at about 500 K, which is attributed to recombinative desorption of tert-butyl ((CH3)(3)CO) and OH groups. More interestingly, a low-temperature pathway possibly producing an alkene product on the oxidized surface was observed. Our results demonstrate that surface oxidation can not only enhance iso-C4H8 production via the dehydration of (CH3)(3)COH but also alter reaction channels, which provides a deeper insight into oxide-based catalysis.