Photocatalytic Decomposition Of Nitric Oxide Over Ag/H-ZSM-5 Catalyst

NO_X is one of the major pollutants in the atmosphere, and the abatement of NO_X has been a hotspot of study all over the world. In recent years, Photocatalytic decomposition of NO has attracted much attention. In this paper, the preparation and characterization of Ag/H-ZSM-5 catalyst and their Photocatalytic reactivity for NO decomposition will be discussed. The main experimental results and conclusions by various techniques are summarized as follows:1. Silver introduced into H-ZSM-5 zeolite greatly enhanced the Photocatalytic activity of NO decomposition, and silver should be the active center for Photocatalytic decomposition of NO.2. The Photocatalytic activity of NO decomposition over Ag/H-ZSM-5 catalyst varies with the pretreated conditions: it is highest when the silver catalyst is pretreated in 20% O₂/He for 1 h at 500℃, and it takes the second place after N₂ pretreatment at the same condition. However, the catalyst shows no Photocatalytic activity when it is preparated in H₂ at 500℃for 1 h.3. The states of silver species over Ag/H-ZSM-S catalysts after the pretreatment in different gas streams are investigated by UV-vis and DRIFTS, the results indicate that: when silver catalyst is pretreated in N₂ at 500℃for 1 h, silver exists as highly dispersed silver ions, silver clusters and nano-sized silver particles. After the pretreatment in 20% O₂/He at 500℃for 1 h, there are more silver ions formed over the sample. Howerver, the nano-sized silver particles become the dominant species after the pretreatment in H₂ at 500℃for 1 h. And there are seldom isolated silver ions over H₂-pretreated sample.4. Combining the characterization results with activity measurements, highly dispersed silver ions in the zeolite should be the active centers for Photocatalytic decomposition of NO.5. The mechanism of the deactivate of silver catalyst for Photocatalytic decomposition of NO is imputed to the poison effect of NO₂^- on Ag^+*(4d⁹5s¹). The catalyst can be partly regenerated by flushing in N₂ at 500℃, however, it can not be regenerated by photo-excitated.