Investigations of sulfur tolerance of water-gas shift catalysts

Conference · Wed Jan 01 04:00:00 EST 1986

OSTI ID:5916524

Campbell, C T

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
• Country of Publication: United States
• Language: English

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ALKALI METALS
CATALYSTS
CATALYTIC EFFECTS
CESIUM
CHALCOGENIDES
COAL GASIFICATION
COHERENT SCATTERING
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SULFUR COMPOUNDS
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