Thermodynamics of the oxidation of rare earth oxysulfides at high temperatures

Dwivedi, R. K.; Kay, D. A. R.

doi:10.1007/bf02657383

Cited by 24 publications

(12 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Under neutral and mildly reducing conditions, the stable species in the presence of sulfur is reported to be Ce 2 (SO 4 ) 3 [15]. Ce, unlike the other rare-earth metals, is not known to form an oxysulfate of the form Ce 2 O 2 SO 4 [16]. With decreasing O 2 fugacity, Ce 2 (SO 4 ) 3 decomposes, first to CeO 2 and then to Ce 2 O 2 S [15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

An Examination of Sulfur Poisoning on Pd/Ceria Catalysts

Luo

Vohs

Gorte

2002

Journal of Catalysis

114

View full text Add to dashboard Cite

The species formed by exposure of a Pd/ceria catalyst to SO 2 under various conditions have been studied using temperature-programmed desorption (TPD) and FTIR. For adsorption of SO 2 between 298 and 473 K, a molecular SO 2 species adsorbs on the surface, possibly as a surface sulfite; and this species converts to a sulfate above 473 K. Exposure of Pd/ceria to SO 2 at temperatures above 473 K in the presence of O 2 results in the formation of bulk sulfates. These sulfates decompose to form SO 2 and O 2 upon TPD in He, with O 2 and SO 2 peaks at 1023 K assigned to Ce +4 sulfates and peaks at 1123 K assigned to Ce +3 sulfates. When H 2 is present in the TPD carrier gas, the sulfates are reduced and a significant fraction of the sulfur is removed as H 2 S, with the rest remaining as Ce 2 O 2 S. When CO is present in the TPD carrier gas, all of the sulfates are reduced to Ce 2 O 2 S, with the simultaneous formation of CO 2. The formation of CO 2 from the reduction of the sulfate occurs in the same temperature range as CO 2 production from reduction of Pd/ceria, except that more CO 2 is formed from the sulfur-poisoned catalyst. The implications of these results for understanding oxygen storage capacity (OSC) in automotive, three-way catalysts is discussed.

show abstract

Section: Introductionmentioning

confidence: 99%

An Examination of Sulfur Poisoning on Pd/Ceria Catalysts

Luo

Vohs

Gorte

2002

Journal of Catalysis

114

View full text Add to dashboard Cite

show abstract

“…Although there could easily be different thermodynamic pathways, the products achieved through the processing conditions used in this research seem to follow the described pattern. It follows a trend that a resin sulfate matrix is decomposed in air and reduced to the oxysulfide (Nd 2 O 2 S) using a H 2 /Ar gas, which is then oxidized in air to the oxysulfate (Nd 2 O 2 SO 4 ) and then further oxidized into the oxide (Nd 2 O 3 ) [13]. It has been shown that in similar atmospheres, curium has comparable decomposition intermediates [14].…”

Section: Discussionmentioning

confidence: 96%

Decomposition Analysis of Neodymium Loaded Resin

Hunley¹,

Voit²

2013

View full text Add to dashboard Cite

“…Under neutral and mildly reducing conditions, the stable species in the presence of sulfur is reported to be Ce 2 (S0 4 ) 3 [36]. Notice that Ce, unlike the other rare-earth metals, is not known to form an oxysulfate of the form Ce 2 0 2 S0 4 [35]. With decreasing 0 2 fugacity, Ce 2 (S0 4 ) 3 decomposes, first to Ce0 2 and then to Ce 2 0 2 S [33 -36].…”

Section: Thermodynamic Considerationsmentioning

confidence: 96%

“…Therefore, thermodynamic properties for sulfur-containing compounds with cerium have been measured and are reasonably well known [33][34][35][36]. The particular compounds that form depend on the fugacities (or partial pressures) of 0 2 and of S 2 , H 2 S, or S0 2 .…”

Section: Thermodynamic Considerationsmentioning

confidence: 99%

SO₂ POISONING OF CERIA-SUPPORTED, METAL CATALYSTS

Gorte¹,

Luo²

2002

Catalysis by Ceria and Related Materials

View full text Add to dashboard Cite

IntroductionAutomobiles have been equipped with catalytic converters since 1975 in the US and since 1986 in Europe [1]. The emissions limits for CO, NO, and hydrocarbons have been steadily decreasing since that time in both regions of the world, requiring improved catalysts and emissions-control systems. A major advance in the development of three-way emissions-control catalysts was the addition of ceria, which is added primarily to provide oxygen-storage capacity (OSC) to allow the oxidation of hydrocarbons and CO to occur simultaneously with the reduction of NO [2]. While the OSC properties in early ceria-containing catalysts were prone to deactivation during high-temperature aging [3], the redox properties of ceria in modern catalysts are stabilized by the addition of zirconia and are very durable, even in the very harsh, high-temperature, hydrothermal environment of the catalytic converter [4].The current generation of catalysts would be sufficient to meet some of the most stringent requirements if sulfur were not present in essentially all hydrocarbon fuels. The combustion of sulfur-containing fuels produces S0 2 in the engine exhaust. In high concentrations and for reducing environments, S0 2 poisons sites on the precious-metal catalysts by forming adsorbed sulfur atoms, which in turn block a portion of the active metal sites and reduce the activity of adjacent metal sites [5].However, for the relatively low sulfur concentrations to which three-way catalyst are typically exposed, the precious metals are usually unaffected. Poisoning of ceria is much more serious than poisoning of the precious metal at the levels of 5 to 20 ppm S0 2 currently present in the typical automotive exhaust. At these concentrations, S0 2 interacts primarily with the ceria-containing component of in the catalytic converter and it is this poisoning of ceria that appears to be the primary problem associated with sulfur poisoning [6][7][8][9][10][11]. The evidence for this is strong. For 377 Catalysis by Ceria and Related Materials Downloaded from www.worldscientific.com by UNIVERSITY OF BIRMINGHAM LIBRARY -INFORMATION SERVICES on 03/21/15. For personal use only.

show abstract

Thermodynamics of the oxidation of rare earth oxysulfides at high temperatures

Cited by 24 publications

References 4 publications

An Examination of Sulfur Poisoning on Pd/Ceria Catalysts

An Examination of Sulfur Poisoning on Pd/Ceria Catalysts

Decomposition Analysis of Neodymium Loaded Resin

SO₂ POISONING OF CERIA-SUPPORTED, METAL CATALYSTS

Contact Info

Product

Resources

About

Thermodynamics of the oxidation of rare earth oxysulfides at high temperatures

Cited by 24 publications

References 4 publications

An Examination of Sulfur Poisoning on Pd/Ceria Catalysts

An Examination of Sulfur Poisoning on Pd/Ceria Catalysts

Decomposition Analysis of Neodymium Loaded Resin

SO2 POISONING OF CERIA-SUPPORTED, METAL CATALYSTS

Contact Info

Product

Resources

About

SO₂ POISONING OF CERIA-SUPPORTED, METAL CATALYSTS