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ADSORPTION AND CATALYTIC DESTRUCTION OF TRICHLOROETHYLENE IN HYDROPHOBIC ZEOLITES
Citation:
Chintawar, P. S. AND H. L. Greene. ADSORPTION AND CATALYTIC DESTRUCTION OF TRICHLOROETHYLENE IN HYDROPHOBIC ZEOLITES. APPLIED CATALYSIS B: ENVIRONMENTAL 14:37-47, (1997).
Description:
Several chromium exchanged ZSM-5 zeolites of varying SiO2/Al2O3 ratio were prepared and investigated for ambient (23 ?C) adsorption and subsequent oxidative destruction (250-400 ?C) of gaseous trichloroethylene (TCE, Cl2C=CHCl) in a humid air stream. With an increase in the SiO2/Al2)3 ratio from 30 to 120, the TCE saturation capacity of these dual-function sorbent/catalyst (S/C) media was found to increase from 6.0 to 10.1 wt% in a humid air stream. This phenomenon was attributed to an increase in the hydrophobicity coupled with reduced steric hindrance and site competition for the adsorption of TCE molecules in the competitive adsorption of TCE and water. Ambient TCE adsorption experiments carried out in dry air also showed the same trend, which was attributed to increasing organophilicity of the S/C media with an increase in the SiO2/Al2O3 ratio. In order to gain knowledge of physisorption sites for TCE molecules in the ZSM-5 structure, temperature-programmed-desorption over a temperature range of 30 60 300 ?C and in-situ FT-IR studies at ambient conditions were also carried out. These studies revealed that in all zeolites (except for Cr-ZSM-5 with SiO2/Al2O3 ratio of 120) TCE interacted with terminal silanol (SiOH) and AlOH groups. At temperatures >/=300 ?C. (with the exception of CrZSM-5 with SiO2/Al2O3 ratio of 120), all S/C media showed >95% TCE destruction efficiency. Based on the adsorption capacity and the activity for oxidative destruction of TCE, it is concluded that the Cr-ZSM-5 S/C medium with SiO2/Al2O3 ratio of 80 gives preferred performance both as a sorbent and a catalyst.