Polarization-dependent total-reflection fluorescence XAFS study of Mo oxides on a rutile TiO2(110) single crystal surface

The structure of well-dispersed Mo oxides on TiO2( 110) was investigated by means of polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-EXAFS) in three different directions of the single-crystal surface. A model sample for supported Mo oxide catalysts was prepared by impregnation of (NH4)(6)Mo7O24. 4H(2)O dissolved in ultrapure water, followed by calcination at 773 K. Direct comparison of the observed EXAFS and the calculated one was performed based on three-dimensional model structures. We found that anisotropic Mo dimers were preferentially formed on the TiO2(110) surface, with Mo-Mo distance (0.335 nm) parallel to the [1(1) over bar 0] direction of the surface. It was also found that the Mo dimers were attached to the surface, showing Mo-Ti (interfacial) distance at 0.296 nm.