Investigation of the decomposition mechanism of hexachlorobenzene on gamma-Al2O3.

Decomposition of hexachlorobenzene (HCB) on high surface area y-alumina was comprehensively studied using in situ Fourier transform infrared spectroscopy, gas chromatography/mass spectrometry (GC-MS) and ion chromatography. Monitoring of the temperature-dependent decomposition by Fourier transform infrared spectroscopy showed that HCB decomposed as the temperature increased and phenolate species and other decomposition products formed. Pentachlorophenol (PeCP) and pentachlorobenzene were identified as the main decomposition products by GC-MS, and the time dependence of the formation of PeCP and pentachlorobenzene suggested that PeCP was the main intermediate. A trace analytical method based on derivatization and GC-MS revealed the presence of 3,4,5,6-tetrachloro-1,2-benzenediol and tetrachloro-hydroquinone. A small amount of inorganic chlorine ions produced by dechlorination of HCB was detected by ion chromatography. PeCP was the main intermediate and was transformed to 3,4,5,6-tetrachloro-1,2-benzenediol and tetrachloro-hydroquinone on the alumina surface. These compounds then decomposed to small molecules via cracking of their aromatic rings.