Mineralization of CCl₄ with copper oxide

Experimentally, CCl₄ was effectively mineralized by CuO to yield stable inorganic species of CO₂ and CuCl₂ (CCl₄ + 2CuO → 2CuCl₂ + CO₂). High CCl₄ conversions (63-83%) were found in the mineralization process performed at 513-603 K for 10-30 min. Using X-ray-absorption near edge structure (XANES) and X-ray photoelectron spectroscopies, we found that most CuCl₂ was encapsulated in the CCl₄-mineralized product solid (mineralization at 513 K for 30 min). At higher mineralization temperatures (563-603 K), CuCl₂ was found to be predominant on the surfaces of the mineralization product. Speciation of copper in the mineralization product solid was also studied by extended X-ray absorption fine structure (EXAFS) spectroscopy. Bond distances of Cu-O and Cu-Cl in the CCl₄-mineralized product solid were 1.93-1.94 and 2.10-2.12 Å, respectively, which were greater than those of normal CuO and CuCl₂ by 0.03-0.07 Å. The increase of the bond distances for Cu-O and Cu-Cl might be due to Cl insertion and concomitant structural perturbation of unreacted CuO in the mineralization process. For the second shell around copper atom, bond distances of Cu-(O)-Cu also increased by 0.03-0.05 Å, and the coordination numbers of Cu-O and Cu-(O)-Cu decreased, as expected, in the mineralization process. In addition, stoichiometrically excess oxygen atoms were found on the solid surfaces, and they might play an important role in the mineralization of CCl₄, leading to the formation of CO₂ and Cl. Chloride atoms might be further captured by CuO, yielding CuCl₂ in the mineralization process. This work exemplifies the utilization of X-ray spectroscopies (XANES, EXAFS, and XPS) to reveal the speciation and possible reaction pathway in a very complex mineralization process in detail.