Study of the Nature and Location of Silver in Ag-Exchanged Mordenite Catalysts. Characterization by Spectroscopic Techniques

Aspromonte, Soledad Guadalupe; Mizrahi, Martín; Schneeberger, Florencia A.; Lopez, Jose Martin Ramallo; Boix, Alicia Viviana

doi:10.1021/jp4046269

Cited by 60 publications

(53 citation statements)

References 56 publications

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“…[27] To assess the oxidation state(s) of extra-framework Lewis acids ites in Ag-ZSM-5, we used X-ray photoelectron spectroscopy (XPS)t oc haracterize as-prepared and calcined Ag 25 -ZSM-5. XPS spectra ( Figure 1B)r eveal two bands at 375.3 and 369.3 eV separated by 6eV, which are assigned to Ag 3d 3/2 andA g3d 5/2 ,r espectively.T hese two characteristic bands are consistent with reported values of Ag-ZSM-5 and AgNO 3 , [28] indicating that both as-prepared and calcined Ag 25 -ZSM-5 are predominantly comprised of Ag + species. Interestingly,X PS surfacea nalysis of as-prepared Ag 25 -ZSM-5 indicates an Ag/Al ratio that is nearly two-fold higher than the value measured by EDX (0.24 AE 0.07).…”

Section: Resultssupporting

confidence: 88%

Silver‐Promoted Dehydroaromatization of Ethylene over ZSM‐5 Catalysts

et al. 2017

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The shape selectivity of ZSM‐5 (MFI type) catalysts is ideal for the production of C6–C8 aromatics. Developing high‐performance zeolite catalysts with improved selectivity to aromatics, particularly from diversified (non‐petroleum) feedstocks, has broad commercial appeal. Non‐oxidative coupling (NOC) of ethylene was examined over Ag‐ZSM‐5 catalysts at 400 °C and shows that Ag+ sites promote dehydroaromatization with enhanced selectivity to toluene and xylenes. Metal exchange of H‐ZSM‐5 results in Ag zoning wherein Ag+ site density is higher on the exterior of ZSM‐5 particles. Catalyst performance was characterized with varying Ag loading as well as the use of methane co‐feed. Aromatic selectivity is about 60 % on Ag‐ZSM‐5 compared to 20 % on H‐ZSM‐5, which is qualitatively consistent with density functional theory (DFT) showing that ethylene forms strong complexes with Ag+ (Lewis acid) sites. DFT calculations also reveal that ethylene activation on H+ (Brønsted acid) sites is more energetically favorable, and likely constitutes the first mechanistic step in ethylene‐to‐liquids (ETL) reactions. Ag‐ZSM‐5 is thus identified as an effective catalyst for low‐temperature ETL reactions that has the potential to outperform conventional metal‐exchanged zeolites.

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Section: Resultssupporting

confidence: 88%

Silver‐Promoted Dehydroaromatization of Ethylene over ZSM‐5 Catalysts

et al. 2017

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“…The curves indicate that there is no further increase in iodine loading capacity beyond the reduction conditions of 673 K and 24 h, which indicated that, at these optimal conditions, the AgZ was fully reduced. Therefore, this set of conditions is the optimal reduction conditions for the AgZ used in the current study and is supported by similar studies in the literature …”

Section: Resultssupporting

confidence: 78%

“…In theory, if all of the 12.0 wt % (1.10 mmol Ag/g) silver was reacted with iodine through the reaction 2Ag + I 2 → 2AgI to form AgI, the theoretical maximum iodine adsorption capacity of the Ag 0 Z would be 14.1 wt % (1.10 mmol I/g). It is noted that before reduction Ag is largely in the crystalline framework of AgZ as

{Ag}_{x}^{+}

(AlO 4 ) −1 x (SiO 2 ) 5 x and that after reduction in hydrogen at 673 K for 24 h or more severe conditions, Ag was shown to be reduced to Ag 0 by XRD and XAFS analysis …”

Section: Methodsmentioning

confidence: 99%

Adsorption of iodine on hydrogen‐reduced silver‐exchanged mordenite: Experiments and modeling

2016

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The adsorption process of iodine, a major volatile radionuclide in the off‐gas streams of spent nuclear fuel reprocessing, on hydrogen‐reduced silver‐exchanged mordenite (Ag0Z) was studied at the micro‐scale. The gas‐solid mass transfer and reaction involved in the adsorption process were investigated and evaluated with appropriate models. Optimal conditions for reducing the silver‐exchanged mordenite (AgZ) in a hydrogen stream were determined. Kinetic and equilibrium data of iodine adsorption on Ag0Z were obtained by performing single‐layer adsorption experiments with experimental systems of high precision at 373–473 K over various iodine concentrations. Results indicate approximately 91% to 97% of the iodine adsorption was through the silver‐iodine reaction. The effect of temperature on the iodine loading capacity of Ag0Z was discussed. The Shrinking Core model describes the data well, and the primary rate controlling mechanisms were macro‐pore diffusion and silver‐iodine reaction. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1024–1035, 2017

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“…[163][164][165][166][167][168] In the particular case of the capture of iodine species, the adsorption properties and cation exchange capacities of zeolites make them interesting and remarkable candidates for this application. In the literature, several zeolites of different structural types have been studied for the capture of iodine species, such as mordenite (MOR structural type), 29,34,74,76,77,79,80,[169][170][171][172][173][174][175][176][177][178] NaX and NaY zeolites (FAU type), 5,60,75,77,78,88,132,179 ZSM-5 (MFI type), 74,77 ferrierite (FER type) and zeolite beta (*BEA type) 74,77 (ESI, Table 3 †).…”

Section: Ag-exchanged Zeolitesmentioning

confidence: 99%