Catalytic decomposition and oxidation of CH3Cl on Cr2O3-doped SnO2 Original Research Article

The adsorption, decomposition and oxidation of CH3Cl have been investigated on pure and chromiadoped SnO2 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 Cr3+ ions incorporated in the surface layer of SnO2 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 CH3Cl interacts with the OH groups of SnO2 at 200–300 K to form H-bridge-bonded alkyl chloride. The decomposition of CH3Cl occurred slowly on pure SnO2 above 573 K to give CH4, H2O, CO and HCl. The oxidation of CH3Cl on SnO2 proceeded at a measurable rate at 400–440 K. Incorporation of a small amount of chromium ions into the SnO2 increased the rate of both the decomposition and the oxidation by a factor of 10–16. The enhanced activity of chromia-doped SnO2 is attributed to the high reactivity of chromium ions in the surface layer of SnO2.