Investigations of sulfur tolerance of water-gas shift catalysts
The interaction of H/sub 2/S with Cu(111) has been investigated. The adsorption proceeds dissociatively, with evolution of H/sub 2/ gas and deposition of S/sub a/. At 300K, the sticking probability (0.02) is constant up to nearly saturation coverage. By 650K, the dissociative sticking probability has decreased by a factor of 3.5. Removal of S/sub a/ using H/sub 2/ pressures up to 1000 torr was impossible, indicating a very slow reverse reaction. This helps explain why such low levels of sulfur can completely poison Cu-based catalysts. Figure 1 shows the influence of pre-adsorbed sulfur on the activity of Cu(111) for WGS at 10 torr H/sub 2/O, 26 torr CO and 625K. There is a linear decay in rate up to saturation coverage, where the rate drops to zero. This linear decay indicates a simple site-blocking mechanism for sulfur poisoning, with only a small ensemble of free Cu sites (less than or equal to2) required for the WGS reaction. The Cu(111) surface was dosed with Cs from a droplet of CsOH solution in ultra-pure water, which was dried by heating mildly (375K, 1 min) in air. The cesium coverage was controlled by the initial Cs concentration in solution. The Cs-dosed catalyst has been characterized by XPS and ISS. Under WGS reaction conditions, the surface was reduced to a state involving, at most, one oxygen atom per Cs adatom. Figure 2 shows the influence of Cs upon the WGS kinetics at 625K, 10 torr H/sub 2/O and 26 torr CO. There is a nearly linear increase in catalyst activity with Cs coverage until a p(2 x 2) LEED pattern appears after reaction (theta/sub Cs/ = 0.25). At this point, the activity is some 15x higher than for unpromoted Cu(111). Pure Cs on Cu(111) also gives a p(2 x 2) LEED pattern at saturation (theta/sub Cs/ = 0.25). For the optimally-promoted surface, the reaction order with respect to H/sub 2/O was the same as for clean Cu(111), and the activation energy increased slightly to 23 kcal/mole/sup -1/.
- Research Organization:
- Los Alamos National Lab., NM (USA); Indiana Univ., Bloomington (USA). Dept. of Chemistry
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 5916524
- Report Number(s):
- LA-UR-86-1887; CONF-860649-1; ON: DE86011227
- Resource Relation:
- Conference: 6. annual gasification contractors' meeting, Morgantown, WV, USA, 24 Jun 1986; Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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COPPER
CATALYTIC EFFECTS
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CATALYSTS
ZINC OXIDES
DEACTIVATION
CESIUM
COAL GASIFICATION
ELECTRON DIFFRACTION
EXPERIMENTAL DATA
HYDROGEN SULFIDES
PROMOTERS
SYNTHESIS GAS
ALKALI METALS
CHALCOGENIDES
COHERENT SCATTERING
DATA
DIFFRACTION
ELEMENTS
FLUIDS
GASES
GASIFICATION
HYDROGEN COMPOUNDS
INFORMATION
METALS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
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SULFUR COMPOUNDS
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENTS
ZINC COMPOUNDS
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