Variable-temperature IR spectroscopic studies of CO adsorbed on Na-ZSM-5 and Na-Y zeolites

CO interacts with extra-framework alkali metal cations (M+) of zeolites to form both M+... CO and M+... OC species. By using variable-temperature FTIR spectroscopy, these C-bonded and O-bonded species were found to be in a te mperature-dependent equilibrium. For the same cation, the difference in int eraction energy depends upon the zeolite framework. Thus, for the equilibri um process ZNa(+)... CO reversible arrow ZNa(+)... OC, where Z represents t he zeolite framework, delta H-0 was found to take the values 3.8 and 2.4 kJ mol(-1) for CO/Na-ZSM-5 and CO/Na-Y, respectively. The C-bonded species sh ow always the highest cation-CO interaction energy.