Ozone-Assisted Catalysis of Toluene with Layered ZSM-5 and Ag/ZSM-5 Zeolites

This paper presents a new type of ozone-assisted catalysis for toluene decomposition. The different catalytic activities of ZSM-5 and Ag/ZSM-5 were incorporated into a layered catalyst with a tandem configuration. Instead of increasing the amount of metal catalyst, the layered catalyst was formed, which had an equal amount of bare ZSM-5 and Ag/ZSM-5 and could achieve both high toluene conversion and CO2 selectivity concurrently. The properties of each catalyst were evaluated with respect to toluene conversion, formation of intermediates, CO2 selectivity and ozone demand factor. The bare ZSM-5 exhibited higher toluene conversion than the Ag/ZSM-5, while its activity toward deep oxidation was limited. However, the Ag/ZSM-5 was found to be effective for the deep oxidation of reaction intermediates (HCOOH and CO). Separate oxidation tests with HCOOH and CO revealed that the ZSM-5-supported Ag nanoparticles could oxidize the HCOOH and CO in the absence of ozone, which was not possible with the bare ZSM-5. Plausible pathways for the oxidation of toluene with O3 over ZSM-5 and Ag/ZSM-5 were proposed based on the experimental evidence.