A supported Au/HZSM-5 catalyst for toluene removal by air plasma catalytic oxidation using the cycled storage-discharge (CSD) mode†

Abstract

Air plasma catalytic oxidation of toluene (C₇H₈) with the cycled storage-discharge (CSD) mode is a promising technology for toluene (C₇H₈) removal. However, the problem of low CO₂ selectivity must be solved. In this work, a novel HZSM-5 (HZ) supported Au catalyst (Au/HZ) with ca. 5.7 nm Au nanoparticles was prepared by combining impregnation-ammonia washing and plasma treatment, and adopted for C₇H₈ removal. Au/HZ displays a large breakthrough capacity and an excellent oxidation ability of C₇H₈ in dry and wet air plasma. To investigate the mechanism of CO₂ selectivity improvement with the Au/HZ catalyst, air plasma catalytic oxidation of gaseous C₇H₈ and CO, as well as the adsorption of C₇H₈ and CO on the catalysts were conducted. For plasma-catalytic oxidation of gaseous C₇H₈ over Au/HZ, the CO₂ selectivity is 97.5%, significantly higher than those of HZ (55%) and Ag/HZ (62%). In situ TPD tests indicate that Au/HZ possesses a moderate adsorption strength for CO and C₇H₈ compared with HZ and Ag/HZ. Meanwhile, plasma oxidation of CO over Au/HZ reaches 100%, which is much higher than those of HZ (15%) and Ag/HZ (24%). Nearly 100% C₇H₈ conversion and CO₂ selectivity of plasma-catalytic oxidation of C₇H₈ on Au/HZ can be attributed to the moderate adsorption strength of Au/HZ for C₇H₈ and CO, and very high plasma catalytic activity for CO oxidation.