Energetic heterogeneity of Cu~+-carbonyl complexes in Y zeolites: Kinetics of CO desorption studied by FTIR combined with CO adsorption microcalorimetry

摘要

We analyzed IR spectra of the isothermal (RT) time-dependent CO desorption on Cu~+Me~+H~+-Y zeolites (Me = Li, Na, K) in order to investigate the energetic heterogeneity of Cu~+-CO species. After spectrum deconvolution, integral band area is plotted as a function of time and fitted by several kinetic models. The combination of three first-order kinetic processes has to be used for accurate description of CO desorption process for all tested IR bands. Under the band, carbonyl complexes are substantially differing in desorption rate contribution. The energy gap of complexes with similar geometry is ascribed to variable original Cu siting. Cu moves toward faujasite supercage where the adsorption proceeds: the higher the Cu interaction with framework the lower the stability of corresponding carbonyl complex. Stability of carbonyl IR band decreases with wavenumber. Lower frequency bands, due to Cu+ at II sites with 2 (or 3) Al at 6T ring, are characterized by significant population of low-stable carbonyls. IR stabilities are well correlated with CO heats of adsorption and changes on calorimetric curves justifying the kinetic evaluation. The influence of zeolite composition, namely Cu loading and kind of co-cation, on the character of IR spectrum and population of energetic components is discussed.