Steam effects in three-way catalysis

Barbier, J.; Duprez, Daniel

doi:10.1016/0926-3373(94)80046-4

Cited by 184 publications

(94 citation statements)

References 130 publications

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“…Although previous reviews have addressed the issue of Pd catalyst stability in the presence or absence of H2O [4,12,20,25], and several catalyst deactivation mechanisms are possible at the exhaust gas conditions [26], several unresolved issues remain. More recent studies of the past decade have provided new insights into the effects of H2O, especially at lower temperatures, and these are the focus of the present review.…”

mentioning

confidence: 99%

Deactivation of Pd Catalysts by Water during Low Temperature Methane Oxidation Relevant to Natural Gas Vehicle Converters

2015

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Abstract:Effects of H2O on the activity and deactivation of Pd catalysts used for the oxidation of unburned CH4 present in the exhaust gas of natural-gas vehicles (NGVs) are reviewed. CH4 oxidation in a catalytic converter is limited by low exhaust gas temperatures (500-550 °C) and low concentrations of CH4 (400-1500 ppmv) that must be reacted in the presence of large quantities of H2O (10-15%) and CO2 (15%), under transient exhaust gas flows, temperatures, and compositions. Although Pd catalysts have the highest known activity for CH4 oxidation, water-induced sintering and reaction inhibition by H2O deactivate these catalysts. Recent studies have shown the reversible inhibition by H2O adsorption causes a significant drop in catalyst activity at lower reaction temperatures (below 450 °C), but its effect decreases (water adsorption becomes more reversible) with increasing reaction temperature. Thus above 500 °C H2O inhibition is negligible, while Pd sintering and occlusion by support species become more important. H2O inhibition is postulated to occur by either formation of relatively stable Pd(OH)2 and/or partial blocking by OH groups of the O exchange between the support and Pd active sites thereby suppressing catalytic activity. Evidence from FTIR and isotopic labeling favors the latter route. Pd catalyst design, including incorporation of a second noble metal (Rh or Pt) and supports high O mobility (e.g., CeO2) are known to improve catalyst activity and stability. Kinetic studies of CH4 oxidation at conditions relevant to natural gas vehicles have OPEN ACCESSCatalysts 2015, 5 562 quantified the thermodynamics and kinetics of competitive H2O adsorption and Pd(OH)2 formation, but none have addressed effects of H2O on O mobility.

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confidence: 99%

Deactivation of Pd Catalysts by Water during Low Temperature Methane Oxidation Relevant to Natural Gas Vehicle Converters

2015

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“…[6] The oxidation-reduction, or regenerative mechanism of Rideal-Elay type, in which water oxidizes the surface and CO re-reduces the oxidized surface. [15,19] Others describe a bi-functional process where the adsorbed CO on the precious metal or mixed metal oxide is oxidized by the support and then water fills the support oxygen vacancy: [19][20][21] …”

Section: Mechanisms and Kineticsmentioning

confidence: 99%

“…Others describe the bifunctional nature where CO adsorbed on the reduced metal migrates to react with hydroxyl groups to produce the formate intermediate. [13,19] FTIR analysis has been commonly used to confirm the presence of the formate intermediate:…”

Section: Mechanisms and Kineticsmentioning

confidence: 99%

“…[7,19] Based on kinetic results two types of mechanisms were proposed. [6] The oxidation-reduction, or regenerative mechanism of Rideal-Elay type, in which water oxidizes the surface and CO re-reduces the oxidized surface.…”

Section: Mechanisms and Kineticsmentioning

confidence: 99%

“…[31] Much attention was focused on the WGS reaction as it applied to automotive exhaust catalysts with respect to CO emissions in the 1970s and 1980s. [19,[34][35][36][37][38][39][40] Detailed and excellent reviews of the early work are given by Kummer and Taylor. [34,35,41] Many have reported that CeO 2 promoted the WGS reaction.…”

Section: Role Of Wgs For Automotive Exhaust Gas Cleaning Systemsmentioning

confidence: 99%

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Catalyst development for water–gas shift

Ladebeck¹,

Wagner²

2010

Handbook of Fuel Cells

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In the industrial production of hydrogen and of synthesis gas the water gas shift reaction represents an essential step for the overall process efficiency of the process by increasing the hydrogen yield and by adjusting the desired ratio of hydrogen and carbon monoxide for a subsequent synthesis step. In addition to that in fuel cell technology it is absolutely necessary to decrease the CO content of the fuel hydrogen due to the limited CO tolerance of present day fuel cell anodes. To be successful applying water gas shift catalysts in hydrogen production for fuel cells especially in automotive systems some major obstacles of the commercial Cu/Zn/Al catalyst systems must be overcome. Major new demands are reduction of volume and weight by two to three orders of magnitude, oxidation resistance and improved tolerance for steam condensation and poisons, here mainly sulfur present in gas feedstock and in gasoline. Precious metal catalyst systems on rare earth metal oxides are most promising and could fulfill the requirements in nonstationary applications were conventional catalysts are not applicable.

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Hydrogen Production and Fuel Cells: Catalyst Technology

Bartholomew

Farrauto²

2005

Fundamentals of Industrial Catalytic Processes

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Steam effects in three-way catalysis

Cited by 184 publications

References 130 publications

Deactivation of Pd Catalysts by Water during Low Temperature Methane Oxidation Relevant to Natural Gas Vehicle Converters

Deactivation of Pd Catalysts by Water during Low Temperature Methane Oxidation Relevant to Natural Gas Vehicle Converters

Catalyst development for water–gas shift

Hydrogen Production and Fuel Cells: Catalyst Technology

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