Angle-resolved and depth profiling XPS investigation of a monolayer niobium oxide catalyst

Abstract

Supports consisting of a thin layer of SiO 2 on a silicon single crystal have been used to study the NbO x /SiO 2/Si(100) model catalyst, obtained by a controlled surface reaction between Nb(OC 2H 5) 5 and silanol groups on the SiO 2 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 × 10 4 mol g −1 with a surface density of 1.25 atoms nm −2.