Abstract
The destructive adsorption of CCl4 on MgO, CaO, SrO, and BaO has been studied as a function of the reaction temperature and the amount of CCl4 injected. The reaction was followed using in situ Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and 13C magic angle spinning nuclear magnetic resonance spectroscopy. It was found that the activity toward CCl4 parallels the basicity of the alkaline earth metal oxide; i.e., the activity decreased in the order BaO > SrO > CaO > MgO. Barium oxide readily reacted with CCl4 at 200−300 °C, and, at these low temperatures, CO2 was the only gas-phase product that evolved from the surface. At higher reaction temperatures, other alkaline earth metal oxides, such as CaO and MgO, also became active, and COCl2 was found to be a reaction intermediate in the destruction of CCl4. Although the destruction process is initiated at the surface, the continuous O2-/Cl- exchange results in the bulk transformation of the metal oxide to the metal chloride. Barium oxide could be regenerated by dissolving the chloride in water, followed by precipitation as barium carbonate and subsequent calcination. In addition, carbon tetrachloride destruction at around 600 °C resulted in the formation of an unusual alkaline earth metal oxide chloride, viz., M4OCl6 (M = Ba, Sr, or Ca).
