Transmission infrared spectroscopy was used to monitor CClx(a) intermediate surface species formed during the decomposition of CCl4 on high surface area calcium oxide. Carbon tetrachloride was adsorbed on calcium oxide at 113 K. During CCl4 desorption, additional infrared bands at 801, 787, 775, 765, and 751 cm(-1) were observed in the temperature range 110-250 K. These bands, which disappeared in the temperature range 150-250 K, were attributed to the formation and depletion of CClx(a) species as C-Cl bonds are broken and Ca-Cl bonds are formed on the CaO surface. Carbon tetrachloride (C-13 labeled) was employed to prove that the infrared bands of the surface intermediates were due to C-CI vibrational modes. To compare carbon tetrachloride decomposition on different types of calcium oxides, both autoclave prepared (nanoscale particles) and conventionally prepared CaO were investigated.