Adsorption behavior of nitrogen monoxide on K_xGa_xSn_8-xO₁₆ hollandite

Fine powder of K_xGa_xSn_8-xO₁₆ hollandite was prepared by the sol-gel process using metal alkoxides, and the adsorption behavior of nitrogen monoxide (NO) on it was examined by temperature programmed desorption (TPD) method and in situ diffuse reflectance fourier transform infrared spectroscopy. Any species other than nitrogen monoxide were not detected in the TPD measurement, and the profile showed three stages between 420 and 880 K which were regarded as the desorption of chemically adsorbed NO_x species. This desorption behavior seems well consistent with the spectral changes in the FT-IR measurement. The absorption band at 1270 cm^-1 was decayed in the first stage from 420 to 640 K, and the bands at 1235 and 1570 cm^-1 in the second stage from 640 and 770 K. In the third stage above 770 K, the strong band at 1340 cm^-1 disappeared. These NO_x species on the hollandite were estimated to have a form of NO₃^- in the first and second stages and a form of NO₂^- in the third stage, considering the data on adsorption of nitrogen oxides on La₂O₃ and CaO.