XPS STUDIES OF MOO3 AL2O3 AND MOO3/SIO2 SYSTEMS/

The detailed analysis of the experimental XPS envelopes of the model M oO3/Al2O3 and MoO3/SiO2 systems was performed using a curve fitting pr ocedure. It appeared possible to fit the XPS spectrum of MoO3/Al2O3 sy stem with a single Mo 3d(5/2)-Mo 3d(3/2) doublet which indicates the p resence of only one type of molybdenum(VI) ore-species. In contrast, c urve fitting for MoO3/SiO2 system required two individual Mo 3d(5/2)-M o 3d(3/2) doublets. The first Mo 3d(5/2)-Mo 3d(3/2) doublet with the b inding energy close to that of bulk MoO3 was attributed to three-dimen sional molybdenum(VI) oxo-species. The second Mo 3d(5/2)-Mo 3d(3/2) do ublet shifted to higher binding energy, reflects the presence of monom eric or two-dimensional molybdenum(VI) ore-species which strongly inte ract with silica surface. (C) 1997 Elsevier Science B.V.