Scanning Electron Microscopy
SEM backscattered electron images for unaged AgZ, Ag0Z, and aged Ag0Z in dry air and humid air (d.p. -15 oC) for 1 month are shown in Figure 4. Small particles are observed on the mordenite crystal surface as shown in Figure 4b. White dots in the image indicates that they comprise elements of higher atomic mass than the Al, Si, and O that comprise the zeolite framework. According to the chemical composition of Ag0Z,11 these particles are necessarily composed of Ag atoms. This observation is in agreement with previous works that indicate Ag ions (Ag+) in AgZ are reduced to Ag0 upon reduction in H2with concomitant migration to the mordenite surface and formation of aggregate clusters.14 This is also consistent with their absence in the image of AgZ (Figure 5a). The observed diameter of the Ag0 particles ranged from 0.1 to 1.2 μm. While we expect particles smaller than 0.1 μm also exist, they cannot be observed under the current magnification. Although the I2 loading capacity of Ag0Z aged in dry air and humid air are decreased (Figure 3), a significant amount of Ag0particles are observed on the surface of aged Ag0Z in dry air (Figure 4c) and humid air (Figure 4d). It is because a reduction in amount or size of the Ag0 particles cannot be quantitively observed by the SEM images.