Journal
APPLIED CATALYSIS A-GENERAL
Volume 389, Issue 1-2, Pages 122-130Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.apcata.2010.09.015
Keywords
CO dissociation; Rh-Ni binary metals; Reforming; Methanation; Density functional theory; Sulfur poisoning
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Funding
- US Department of Energy National Energy Technology Laboratory [DE-FC26-08NT0004396]
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The effect of Ni addition to improve the sulfur tolerance of a Rh catalyst for CO dissociation was studied using density functional theory (DFT) methods. Adsorption and dissociation were considered over the (1 1 1) surfaces of binary Rh1Ni2 and Rh2Ni1 metals with comparison to pure Rh and Ni surfaces. Sulfur adsorption on the Rh1Ni2(1 1 1) surface is 0.21 eV more endothermic than on the Rh(1 1 1) surface, suggesting that a Rh1Ni2 bimetallic catalyst has a higher sulfur tolerance than pure Rh catalysts due to a lower surface coverage of the sulfur poison. To compare catalytic activity in the presence of adsorbed sulfur, the CO dissociation rates over the binary and pure metals were calculated with 1/9 sulfur coverage. CO dissociation is fastest on the pure Rh surface under sulfur-free conditions, whereas among sulfur poisoned surfaces, the Rh1Ni2 surface shows the fastest CO dissociation rate. The CO dissociation barrier on Rh1Ni2 is destabilized less by a S coadsorbate than for the other metals. The addition of Ni atoms to a Rh catalyst improves the sulfur tolerance of the catalyst for CO dissociation by minimizing the repulsion between the adsorbed S atom and the CO dissociation transition state, as evidenced through a projected density of states analysis. The Rh1Ni2(2 2 1) stepped surface also shows a lower activation barrier and higher CO dissociation rate in the presence of sulfur than the Rh(2 2 1) stepped surface. (C) 2010 Elsevier B.V. All rights reserved.
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