Effects of water and ion-exchanged counterion on the FT-IR spectra of ZSM-5: Part III.: Cu+(CO)2-ZSM-5:: interaction of Cu+(CO)2 complex with H2O and changes in skeletal T-O-T vibrations

The effect of water on Cu+(CO)(2)-ZSM-5 (n(Si)/n(Al) = 20, n(Cu)/n(Al) = 0.75) has been studied at 293 K by time-resolved FT-IR technique in transmission mode, using self-supporting sample and flow system. After an H2O pulse addition into the CO/He line, (a) the IR bands Of Cu+(CO)(2) di-carbonyls at 2177 (sym) and 2151 cm(-1) (as), (b) the skeletal T-O-T vibrations and (c) the O-H vibrations considerably changed. In spite of the presence of 7.44 Torr (I Torr = 133.3 Pa) CO, water easily and reversibly displaced one carbonyl ligand [i.e. Cu+(CO)(2) + H2O=Cu+(CO)(H2O) + CO], since the relevant FT-IR spectra showed very similar features to those presented recently for the [(Cu+-CO)-ZSM-5 + H2O] system [see, J. Sarkany, Topics in Catalysis 18(2002)271]. Subsequent to H2O addition, only first one nu((CO)-C-12) band appeared (stage C), namely at 2111 cm(-1) which continuously shifted to 2118 cm(-1) with decreasing H2O concentration, then anew band series was observed (stage B) with gradual shifts from 2132 to 2139 cm(-1), while finally the original Cu+((CO)-C-12)(2) twin complex (2177 and 2151 cm(-1)) [and, according to the equilibrium, Cu+((CO)-C-12) mono-carbonyl (2157 cm(-1))] came back (stage A), via an isosbestic point at 2144 cm(-1). Similarly, Cu+((CO)-C-13)((CO)-C-12) mixed di-carbonyls (caused by 1.11% (CO)-C-13 being present naturally in CO) showed also three types of interactions with H2O. Two of them were analogous to [Cu+((CO)-C-13) + H2O] with stages C (2063-2070 cm(-1)) and B (2083-2089 cm(-1)), while stage A revealed only one di-carbonyl-related characteristic band at 2111 cm(-1) due to low-frequency (LF) [or upsilon(as)(CO)] band of Cu+(C-13-O)(C-12-O). The pertinent high-frequency-band (HF-band) [upsilon(sym)(CO)] at 2167-2170 cm(-1) could not be observed because of high overlapping with (very) strong upsilon(CO) bands Of Cu+((CO)-C-12)(2) and Cu+((CO)-C-12) carbonyls, Other frequency regions of the FT-IR spectra also resulted in some useful informations. H2O reversibly interacted at 293 K with zeolitic OH groups and with the whole zeolite ZSM-5. Large amount of H2O notably enhanced the intensities of skeletal vibrations. (C) 2002 Elsevier Science B.V. All rights reserved.