Catalytic decomposition and oxidation of CH 3Cl on Cr 2O 3-doped SnO 2

Abstract

The adsorption, decomposition and oxidation of CH 3Cl have been investigated on pure and chromiadoped SnO 2 catalysts by means of infrared spectroscopy, mass spectrometric and gas chromatographic analysis. Catalyst samples have been characterized by X-ray photoelectron spectroscopy. It was found that the Cr 3+ ions incorporated in the surface layer of SnO 2 are oxidized to higher valent chromium ions. In harmony with the determination of active oxygen content, samples calcined at 873–973 K contained the largest concentration of higher valent chromium ions. Infrared spectroscopy showed that CH 3Cl interacts with the OH groups of SnO 2 at 200–300 K to form H-bridge-bonded alkyl chloride. The decomposition of CH 3Cl occurred slowly on pure SnO 2 above 573 K to give CH 4, H 2O, CO and HCl. The oxidation of CH 3Cl on SnO 2 proceeded at a measurable rate at 400–440 K. Incorporation of a small amount of chromium ions into the SnO 2 increased the rate of both the decomposition and the oxidation by a factor of 10–16. The enhanced activity of chromia-doped SnO 2 is attributed to the high reactivity of chromium ions in the surface layer of SnO 2.