Interaction of Formaldehyde with the Rutile TiO2(110) Surface: A Combined Experimental and Theoretical Study
Yu, X. / Zhang, Z. / Yang, C. / Bebensee, F. / Heissler, S. / Nefedov, A. / Tang, M. / Ge, Q. / Chen, L. / Kay, B., D. / Dohnalek, Z. / Wang, Y. / Wöll, C. (2016)
J. Phys. Chem. C, 120, 12626-12636, DOI: 10.1021/acs.jpcc.6b03689
- Date: Mai 2016
The adsorption and reaction of formaldehyde (CH2O) on the oxidized rutile TiO2(110) surface were studied by temperature programmed desorption (TPD), scanning tunneling microscopy (STM), infrared reflection-absorption spectroscopy (IRRAS) and density functional theory (DFT) calculations. The experimental and theoretical data reveal the presence of various species depending on the temperature and coverage. Exposure to formaldehyde at 65 K leads to the formation of CH2O multilayers, which desorb completely upon heating to 120 K. After smaller exposures at low temperatures (45-65 K), STM allowed to identify individual, isolated CH2O monomers.
The theoretical results indicate that these monomers are bound to the surface Ti5c sites via σ-donation and adopt a tilted geometry. Upon heating, the CH2O monomers polymerize to form paraformaldehyde (polyoxymethylene, POM) chains, oriented primarily along the Ti5c rows ( direction). Upon further heating POM is found to decompose around 250 K, releasing CH2O into the gas phase.
In addition, dioxymethylene (DOM) was detected as minority species formed via reaction of Ti5c-bound CH2O with surface O-atoms. For all substrate species, the characteristic IR vibrations were measured. Since these are the first IRRAS data for TiO2 macroscopic single crystals exposed to formaldehyde, we have performed DFT calculations in order to aid the assignment of the various bands.