A FTIR search for linkage isomerism of CN- ions adsorbed on oxides and zeolites

作者：Tsyganenko A A^*; Chizhik A M; Chizhik A I

来源：Physical Chemistry Chemical Physics, 2010, 12(24): 6387-6395.

DOI：10.1039/c003942j

Adsorption of HCN and DCN was studied at 150-600 K on TiO2, ZnO, MgO and a set of X zeolites by means of FTIR spectroscopy. At the lowest temperatures adsorption is non-dissociative and occurs on surface OH groups of oxides, cations and coordinately unsaturated oxygen atoms. Bands at 2243-2147 cm(-1) assignable to CN- ions start to grow in the spectra of ZnO at 170 K, at 250 K for MgO and at 300 K for TiO2, where bands of polymeric species appear simultaneously. The structure of bands near 2200 cm(-1) in the spectra of the studied oxides does not display a temperature dependence characteristic of isomeric forms. Reversible temperature changes of the band of CN- ions in Na-, K-, Rb- and CsX zeolites exposed to HCN provide evidence for linkage isomerism, when the ions bound to alkali cations via C- or N- atoms co-exist in the thermodynamic equilibrium. C-Bonded species account for the stronger band at 2200-2140 cm(-1), while the low-frequency shoulder of this band, which appears and grows at elevated temperatures, is due to the energetically less favorable N- bonded form. The enthalpy of isomerization, estimated from the temperature dependence of band intensities, decreases from ca 20 kJ mol(-1) or more for Na+ and K+ to 7.6 kJ mol(-1) for Cs+, in accordance with the electrostatic model.

• 出版日期2010