Adsorption of pyridine on copper-silica catalysts is studied by differential scanning calorimetry (DSC) and Fourier
transform-infrared/photoacoustic spectroscopy (FT-IR/PA), in the region of mid-frequency vibrations as well as in the
region of hydroxyl groups. The adsorption of pyridine on copper-silica catalysts shows three modes of sorption in the
1650-1400 cm 1 region: physisorption or hydrogen-bonded (HPY), and two sites of Lewis acid sorption (LPY(I) and
LPY(II)).
The Lewis band at 1609 cm -1 was very strong compared with the 1450 cm 1 band since the former band showed
a shift to higher wavenumbers whereas the latter showed a shift to lower wavenumbers. A relationship was found
between the DSC scans, in the low temperature range (240-140°C), and the 1450-1443 cm-1 band. On the other
hand, the high temperature DSC scans (400-360°C) were correlated with the behaviour of the 1609-1612 cm -1
band.
The volumetric results of pyridine adsorption on 9 and 15 wt.% Cu catalysts show a constant behaviour; however,
this constancy was also reflected by carbon monoxide adsorption, demonstrated by a similar behaviour of both 2128
and 2259 cm -1 bands. This was attributed to the blocking of the small pores of silica earlier at the 9 wt.% Cu loading.
A new broad band at 2248-2259 cm 1, not identified in the ion-exchange catalysts, was obtained and attributed to
CO adsorbed on agglomerated copper clusters. |
