Methane Combustion over Pd/Al2O3 Catalyst: Effects of Chlorine Ions and Water on Catalytic Activity

Gao, Diannan; Wang, Sheng; Zhang, Chunxi; Yuan, Zhengqiu

doi:10.1016/s1872-2067(09)60027-9

Cited by 36 publications

(30 citation statements)

References 20 publications

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“…Despite the reported benefits of water as a cocatalyst, care must be taken to avoid excess water conditions for systems in which H 2 O competitively adsorbs on reaction sites and thereby limits the adsorption of other reactants. An example of strong water inhibition is the oxidation of small alkanes on PdO, where surface hydroxylation has been associated with catalyst deactivation [71].…”

Section: Discussionmentioning

confidence: 99%

Water-assisted oxygen activation during selective oxidation reactions

Tran

Doan

Chandler

et al. 2016

Current Opinion in Chemical Engineering

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Section: Discussionmentioning

confidence: 99%

Water-assisted oxygen activation during selective oxidation reactions

Tran

Doan

Chandler

et al. 2016

Current Opinion in Chemical Engineering

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“…With the growing interest in NGVs, recent studies have focused on effects of H2O on Pd catalysts during CH4 combustion [16,18,[30][31][32][33][34][35][36][37][38]. Deactivation or inhibition effects of H2O are dependent upon several factors including catalyst formulation, reaction temperature, catalyst time-on-stream history, and H2O concentration.…”

Section: Water Concentration and Reaction Temperature Effects On Ch4 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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“…0.24 % of chlorine deposited on used catalyst while chlorine was not detected in the fresh catalyst and used dust (see Table 2). Others have suggested that chlorine ions behaves as a powerful inhibitor during methane oxidation over supported Pd catalyst 11,32,33 and removing the chlorine from the surface takes a minimum 10 h reaction even at temperatures as high as 600 ºC. XPS spectra of Pd 3d core level of used 1.0 wt% Pd/Al2O3 catalyst in the presence of dust, (a) used catalyst; (b) used dust mixed with catalyst.…”

Section: Figmentioning

confidence: 99%