Manipulating the charge state of Au clusters on rutile TiO ₂ (110) single crystal surfaces through molecular reactions probed by infrared spectroscopy

The charge state of Au clusters deposited on rutile TiO2(110) single crystal surfaces was studied by UHV-FTIRS using CO as a probe. The as-deposited Au clusters on oxidized TiO2(110) surfaces are electrically neutral and are identified by the 2105-2112 cm(-1) vibrational frequency of adsorbed CO depending on Au coverage. Annealing Au/TiO2(110) in a moderate O2 atmosphere at 400 K blue shifts the CO vibrational frequency by only 2-3 cm(-1) both on bare TiO2(110) surfaces and on Au clusters. However, NO exposure blue shifts the CO vibrational frequency by 16-26 cm(-1) for CO adsorbed on Au atoms near the interface and by 3-4 cm(-1) for CO adsorbed on top of Au clusters. As the acceptors of the intense charge transfer from Au, the Oa atoms generated through (NO)2→ N2O + Oa reactions on the small fraction of the bare TiO2(110) surface reside around the Au/TiO2(110) interface perimeter, causing the neutral Au(0) to be cationic Au(δ+) states. This is a new approach to manipulate the charge state of Au clusters on oxide surfaces, which may be helpful in regulating the catalytic redox reactions on oxide supported metal systems.