Removal of toluene by sequential adsorption-plasma oxidation: Mixed support and catalyst deactivation

A sequential adsorption-plasma oxidation system was used to remove toluene from simulated dry air using γ-Al₂O₃, HZSM-5, a mixture of the two materials or their supported Mn-Ag catalyst as adsorbents under atmospheric pressure and room temperature. After 120min of plasma oxidation, γ-Al₂O₃ had a better carbon balance (∼75%) than HZSM-5, but the CO₂ yield of γ-Al₂O₃ was only ∼50%; and there was some desorption of toluene when γ-Al₂O₃ was used. When a mixture of HZSM-5 and γ-Al₂O₃ with a mass ratio of 1/2 was used, the carbon balance was up to 90% and 82% of this was CO₂. The adsorption performance and electric discharge characteristics of the mixed supports were tested in order to rationalize this high CO_x yield. After seven cycles of sequential adsorption-plasma oxidation, support and Mn-Ag catalyst deactivation occurred. The support and catalyst were characterized before and after deactivation by SEM, a BET method, XRD, XPS and GC-MS in order to probe the mechanism of their deactivation. 97.6% of the deactivated supports and 76% of the deactivated catalysts could be recovered by O₂ temperature-programmed oxidation.