ANGLE-RESOLVED AND DEPTH PROFILING XPS INVESTIGATION OF A MONOLAYER NIOBIUM OXIDE CATALYST

Supports consisting of a thin layer of SiO2 on a silicon single crystal have been used to study the NbOx/SiO2/Si(100) model catalyst, obtained by a controlled surface reaction between Nb(OC2H5)(5) and silanol groups on the SiO2 support. Characterization of the niobic acid monolayer has been performed by a combination of conventional, angle-resolved and depth profiling X-ray photoelectron spectroscopy (XPS). Compared to the powder analogues, a drastic increase in spectral resolution and detailed band structure is observed in the XPS spectra. The number of attached Nb atoms on the silicagel (specific surface, S-BET = 345 m(2) g(-1); pore diameter, 20 nm) has been determined as 6.86 x 10(4) mol g(-1) with a surface density of 1.25 atoms nm(-2).