Cycled storage-discharge (CSD) plasma catalytic removal of benzene over AgMn/HZSM-5 using air as discharge gas

Abstract

Cycled storage-discharge (CSD) plasma catalytic removal of benzene (C₆H₆) using air as the discharge gas over AgMn/HZSM-5 (AgMn/HZ) catalyst is reported in this study. The properties of AgMn/HZ catalyst were compared with HZ, Mn/HZ, and Ag/HZ catalysts in investigations of C₆H₆ storage capacity and plasma catalytic oxidation of stored C₆H₆. Among HZ, Mn/HZ and Ag/HZ catalysts, the AgMn/HZ catalyst possessed the highest breakthrough capacity of C₆H₆, which is almost twice than that of the unsupported HZ zeolite. For the AgMn/HZ catalyst, stored C₆H₆ is oxidized completely to CO₂ due to the promoting effect of Ag and MnO_x. On the other hand, this accelerates the oxidation rate of stored C₆H₆ during plasma oxidation of stored C₆H₆. The effects of discharge parameters on plasma oxidation of stored C₆H₆ over the AgMn/HZ catalyst are discussed. During the CSD process, under conditions of ∼20 000 mL h⁻¹ g⁻¹ space velocity, 6 W of input power, 0.4 vol% of absolute humidity and 24 min of discharge, the stored C₆H₆ conversion increased rapidly with cycle number during the first three cycles and nearly all stored C₆H₆ could be oxidized into CO₂ thereafter. In addition, CO₂ selectivity was maintained at around 100% and only a small amount of N₂O (40–50 ppm) was detected during all five cycles. Temperature-programmed desorption of adsorbed C₆H₆ on the used AgMn/HZ catalyst indicates that the minor Ag sites, which are highly active, cannot be renewed by the air plasma, but the major Ag sites, which are normally active, are renewable. This explains the variation of stored C₆H₆ conversion with cycle number.