Infrared spectroscopic characterization of basic properties: Nitromethane as probe molecule

Nitromethane, as probe molecule, and infrared spectroscopy, as analytical tool, were used to characterize the basic properties of alkali-exchanged X zeolites and metal oxides. It was observed that this probe molecule could adsorb molecularly, dissociatively and dissociative-associatively, according to the basic strength of the sites present on the studied solids. Alkali-exchanged X zeolites presented weak basic sites and a scale of basicity could be established, CsX > KX >NaX > LiX, based on the shift of the CH3 rock angular bending frequency. On Al2O3, ZrO2, TiO2 weak and intermediate basic sites were identified, while on MgO, La2O3 and alkali-promoted MgO just strong basic sites were found. For the alkali-promoted MgO samples no basicity scale could be observed. For the universe of the studied materials nitromethane behaves as a proper probe molecule to characterize basic sites with different strengths.

Nitromethane, as probe molecule, and infrared spectroscopy were used to characterize basic properties of alkali-exchanged X zeolites and metal oxides. On zeolites the rock angular bending band was sensitive to the electrostatic field produced by the alkali cation and its frequency varies linearly with the ionic radius of the cation.Figure optionsDownload high-quality image (21 K)Download as PowerPoint slide