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Reversible interconversion behavior of Ag species in AgHZSM-5: XRD, 1H MAS NMR, TPR, TPHE, and catalytic studies

Paper ID Volume ID Publish Year Pages File Format Full-Text
43329 45964 2008 8 PDF Available
Title
Reversible interconversion behavior of Ag species in AgHZSM-5: XRD, 1H MAS NMR, TPR, TPHE, and catalytic studies
Abstract

1H MAS NMR, XRD, TPR, TPHE (temperature-programmed hydrogen evolution) techniques, and catalytic characterization by ethanol conversion were employed to investigate the reducibility and reversible interconversion behavior of Ag species in Ag-modified HZSM-5 (3 wt.%). The samples were prepared by ion-exchange of ZSM-5 with AgNO3 (aq). It was found that charge-balancing Ag cations in AgHZSM-5(Si/Al ∼11) and AgHZSM-5(Si/Al ∼28) can be readily reduced to “cationic Ag clusters” at ∼220 °C, while a higher temperature is required for the Ag species in AgHZSM-5(28) to be reduced to “metallic Ag clusters”, as compared with that for AgHZSM-5(11). Both cationic and metallic Ag clusters formed can be reversibly conversed into charge-balancing Ag cations by the reaction with neighboring Brønsted acid sites (reversible interconversion). The metallic Ag clusters were found to be more resistant to the reversible interconversion than the cationic Ag clusters. Under hydrogen stream, the reduced Ag species could be preserved and “silver hydride” species were observed, together with the active Brønsted acid sites. This phenomenon is suggested to play a decisive role on the catalytic activity of AgHZSM-5 towards BTX formation in the presence/absence of hydrogen.

Graphical abstractCharge-balancing Ag cations in AgHZSM-5(Si/Al ∼11) and AgHZSM-5(Si/Al ∼28) can be readily reduced to “cationic Ag clusters” at ∼220 °C, while a higher temperature is required for the Ag species in AgHZSM-5(28) to be reduced to “metallic Ag clusters”, as compared with that for AgHZSM-5(11). Both cationic and metallic Ag clusters formed can be reversibly conversed into charge-balancing Ag cations by the reaction with neighboring Brønsted acid sites.Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Ag-exchanged ZSM-5; Reversible interconversion; MAS NMR
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Reversible interconversion behavior of Ag species in AgHZSM-5: XRD, 1H MAS NMR, TPR, TPHE, and catalytic studies
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 345, Issue 1, 31 July 2008, Pages 89–96
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us