"Characterization of MoOx/ZrO2 System by XPS and IR Spectroscopies"

MoOx/ZrO2 samples (Mo content, 0.7 to 4.0 atoms nm-2) have been investigated by XPS and Fourier transform Infrared (FTIR) spectroscopies. After heating in O2 (773 K), XPS shows the presence of Mo(VI) species; while the IR analysis shows bands in the 830-1012 cm-1 region, arising from Mo(VI) species of various nuclearity. In the early stages of the reduction (H2 at 500 K) both XPS and IR show the formation of Mo(V). In agreement with previous ESR results, the intensity of IR and XPS bands from Mo(V) does not appreciably change by further increasing the extent of reduction up to 803 K. On extensively reduced samples, both IR and XPS show the presence of Mo(IV) in addition to Mo(VI) and Mo(V). Upon NO adsorption at RT, dinitrosyls of Mo(IV) were detected by IR. A further rise in the extent of reduction with H2 at 803 K, led to a drop in the intensity of the IR band from Mo(IV) and XPS detected Mo metal.