Imaging of Formaldehyde Adsorption and Diffusion on TiO2(110)
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Surface reactions of formaldehyde with reduced TiO2(110) surfaces have been studied using variable-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). STM images taken from a same area at various temperatures clearly show that formaldehyde preferentially adsorbs on the bridge-bonded oxygen (Ob) vacancy (VO) defect sites. Bias-dependent STM images show that the STM features corresponding to both the Ti-bound CH2O and the VO-bound CH2O are positioned between the Ob row and the Ti row. While the VO-bound formaldehyde rotates at 95 K, the Ti-bound CH2O does not. The VO-bound CH2O starts to diffuse along the Ob row as –CH2– at ~170 K and starts to diffuse along the Ti row as an intact molecule at ~215 K. However, the stabilities and the configurations of the Ti-bound and VO-bound formaldehyde calculated using DFT are not in line with the experimental results. The discrepancy between the experiment and theory indicates the presence of a complex charge distribution related to the surface defects.
KeywordsTitanium dioxide Formaldehyde Defects Diffusion Scanning tunneling microscope Density function theory
Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. MT and QG acknowledge support by U.S. Department of Energy (DOE) Basic Energy Science (BES) Grant DE-FG-05ER46231. ZW, IL, and ZD were supported by the U.S. DOE BES, Division of Chemical Sciences, Biosciences and Geosciences. Calculations and part of the experimental work and part of the experiments were performed using EMSL, a national scientific user facility sponsored by the DOE Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the U.S. DOE by Battelle Memorial Institute under Contract No. DE-AC06-76RLO 1830.
- 23.Zhu K, Wang Z, Xia Y, Dohnalek Z, Lyubinetsky I, Park KT, Zhang Z Manuscript in preparationGoogle Scholar