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Effect of Ag on the control of Ni-catalyzed carbon formation: A density functional theory study

Paper ID Volume ID Publish Year Pages File Format Full-Text
55482 47055 2012 9 PDF Available
Title
Effect of Ag on the control of Ni-catalyzed carbon formation: A density functional theory study
Abstract

First-principles calculations have been performed to examine the effect of doped Ag on the kinetics of Ni-catalyzed methane dissociation and coke formation. The close-packed Ag/Ni(1 1 1) and stepped Ag/Ni(2 1 1) surfaces as well as the defect facets with step sites blocked by Ag or C atoms are constructed to investigate the role of the coordinatively unsaturated sites in the catalytic performance of Ni nanoparticles. The most stable CHx (x = 0–4) adsorption configurations and transition states for methane dissociation have been identified on both Ni and Ag/Ni surfaces. The calculated results indicate that the activation energy for methane dissociation is increased with the Ag coverage on Ni(1 1 1), and the C atoms deposited on the catalyst surface can be readily separated into small islands by Ag. On Ni(2 1 1) Ag atoms are predicted to bind preferentially to the middle-step sites which act as the nucleation center for the growth of filamentous carbon and therefore have the potential to prevent catalyst particles from being destroyed. Meanwhile, as the energy barrier for methane dissociation on the Ag-blocked Ni(2 1 1) surface is even higher than that on pure Ni(1 1 1), the active center is transferred from the stepped surface to the close-packed surface. These findings provide a rational interpretation of the experimental observations that Ag/Ni catalyst exhibits lower catalytic activity towards steam methane reforming but high resistance to coke deposition.

Graphical abstractDFT calculations have been performed to examine the effect of doped Ag on Ni-catalyzed methane dissociation and coke formation. The doped Ag is likely to suppress the formation of filamentous carbon. The active center is transferred from the stepped surface to the close-packed surface once Ag is introduced into Ni catalyst.Figure optionsDownload full-size imageDownload high-quality image (152 K)Download as PowerPoint slideHighlights► The effect of Ag on Ni-catalyzed coke formation is investigated. ► Methane activation is hindered with the increase of the Ag coverage. ► Step sites dominate methane activation and coke formation. ► The active center is transferred from Ni(2 1 1) to Ni(1 1 1) with the Ag introduction.

Keywords
DFT; Coke resistance; Carbon nanofiber; Steam reforming; Ni; Ag
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Effect of Ag on the control of Ni-catalyzed carbon formation: A density functional theory study
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 186, Issue 1, 1 June 2012, Pages 54–62
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
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Full-text PDF Download
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