I have used PVP-supported metal nanoparticles as a catalyst three times in an oxidation reaction at 100C°. The catalytic result for all three used of the catalyst in the reaction was almost the same and I have measured the bare support and prepared PVP-protected metall nanoparticles after third use of the catalyst (PVP-protected nanoparticles) in the oxidation reaction by IR. But I have found an extra broad signal at 960cm-1 in the spectra after the third use of the catalyst and I do not know to which to attribute it . From the literature I found that bare PVP also has the same vibration at this region so it is possible that the extra signal in the spectra after the third use of the catalyst is attributed to the PVP. If yes, what does it mean and is there another technique to confirm the stability of PVP in the oxidation reaction?