DESTRUCTIVE ADSORPTION OF CARBON-TETRACHLORIDE ON ALKALINE-EARTH METAL-OXIDES

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 CC l4 injected. The reaction was followed using in situ Raman spectroscop y, X-ray photoelectron spectroscop., Fourier transform infrared spectr oscopy, and C-13 magic angle spinning nuclear magnetic resonance spect roscopy. It was found that the activity toward CCl4 parallels the basi city of the alkaline earth metal oxide; i.e., the activity decreased i n the order BaO > SrO > CaO > MgO. Barium oxide readily reacted with C Cl4 at 200-300 degrees C, and, at these low temperatures, CO2 was the only gas-phase product that evolved from the surface. At higher reacti on temperatures, other alkaline earth metal oxides, such as CaO and Mg O, also became active, and COCl2 was found to be a reaction intermedia te in the destruction of CCl4. Although the destruction process is ini tiated at the surface, the continuous O2-/Cl- exchange results in the bulk transformation of the metal oxide to the metal chloride. Barium o xide could be regenerated by dissolving the chloride in water, followe d by precipitation as barium carbonate and subsequent calcination. In addition, carbon tetrachloride destruction at around 600 degrees C res ulted in the formation of an unusual alkaline earth metal oxide chlori de, viz., M4OCl6 (M = Ba, Sr, or Ca).