Dinitrogen and carbon monoxide hydrogen bonding in protonic zeolites: Studies from variable-temperature infrared spectroscopy

Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-Y results in hydrogen bonding of the adsorbed N2 molecules with the zeolite Si(OH)Al Brønsted-acid groups. This hydrogen-bonding interaction leads to activation, in the infrared, of the fundamental N–N stretching mode, which appears at 2334 cm−1. From infrared spectra taken over a temperature range, the standard enthalpy of formation of the OH···N2 complex was found to be ΔH0 = −15.7(±1) kJ mol−1. Similarly, variable-temperature infrared spectroscopy was used to determine the standard enthalpy change involved in formation of H-bonded CO complexes for CO adsorbed on the zeolites H-ZSM-5 and H-FER; the corresponding values of ΔH0 were found to be −29.4(±1) and −28.4(±1) kJ mol−1, respectively. The whole set of results was analysed in the context of other relevant data available in the literature.