TPD-IR studies of CO desorption from zeolites CuY and CuX

The desorption of CO from zeolites CuY and CuX was followed by TPD-IR method. This is a combination of temperature programmed desorption and IR spectroscopy. In this method, the status of activated zeolite (before adsorption), the process of adsorption, and the status of adsorbed molecules can be followed by IR spectroscopy, and the process of desorption (with linear temperature increase) can be followed both by IR spectroscopy and by mass spectrometry. IR spectra have shown two kinds of Cu+ sites in both CuY and CuX Low frequency (l.f.) band (2140 cm(-1) in CuY and 2130 cm(-1) in CuX) of adsorbed CO represents Cu+ sites for which pi back donation is stronger and sigma donation is weaker whereas high frequency h.f. band (2160 cm(-1) in CuY and 2155 cm-1 in CuX) represent Cu+ sites for which pi back donation is weaker and sigma donation is stronger. The TPD-IR experiments evidenced that the Cu+ sites represented by l.f. band bond CO more weakly than those represented by h.f. one, indicating that sigma donation has more important impact to the strength of Cu+-CO bonding. On the contrary, pi back donation has bigger contribution to the activation of adsorbed molecules. (c) 2005 Elsevier B.V. All rights reserved.