Influence of metal oxides on the performance of Pd/Al2O3 catalysts for methane combustion under lean-fuel conditions

Liu, Ying; Wang, Sheng; Gao, Diannan; Sun, Tianjun; Zhang, Chunxi

doi:10.1016/j.fuproc.2013.01.013

Cited by 64 publications

(39 citation statements)

References 51 publications

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“…The effect of metal oxides added to Pd/Al2O3 to improve the hydrothermal stability has been reported by Liu et al [36] who showed in particular, that the addition of NiO or MgO improved the hydrothermal stability of Pd/Al2O3 through the formation of NiAl2O4 and MgAl3O4 spinel structures. According to the authors, the spinel results in weakened support acidity that suppresses the formation of Pd(OH)2 during hydrothermal aging.…”

Section: Effects Of Supportmentioning

confidence: 75%

“…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%

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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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Section: Effects Of Supportmentioning

confidence: 75%

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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“…However, the catalytic activity of these systems is decreasing with time-on-stream and significant research has been addressed to understand the mechanism of Pdbased catalyst deactivation during the methane oxidation. The water inhibition effect has been discussed extensively [4][5][6][7][8][9][10][11][12][13][14][15] and the formation of surface hydroxyls is considered to be a key deactivation pathway, which results in the slow deactivation of the catalyst due to the continuous formation and accumulation of these surface species [8,16]. Moreover, it was shown that competitive adsorption between methane and water molecules plays a role in the catalytic activity loss [5,9,15,17,18].…”

Section: Introductionmentioning

confidence: 99%

An Experimental and Kinetic Modelling Study for Methane Oxidation over Pd-based Catalyst: Inhibition by Water

et al. 2017

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“…Noble metal (such as Pt, Pd) [7][8][9][10] catalysts demonstrate an excellent catalytic performance in CCM at low temperature, but they are limited in commercial application because of high price and rarity. Transition metal (such as Mn, Fe, Cu, Co, Ni, Cu etc.)…”

Section: Introductionmentioning

confidence: 99%

Effect of Co/Ni ratios in cobalt nickel mixed oxide catalysts on methane combustion

Lim

Cho

Yang

et al. 2015

Applied Catalysis A: General

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2Graphical abstract Highlights 1. Co-Ni mixed oxide having the ratios of Co to Ni of (50:50) exhibits the highest activity among the known transition metal oxide catalysts.2. Co-Ni mixed oxides having the ratios of Co to Ni of (50:50) show the highest activity for methane combustion.3. Distorted NiCo2O4 spinel structure plays a key role as the active sites for methane combustion.3 Abstract A series of cobalt nickel mixed oxide catalysts with the varying ratios of Co to Ni, prepared by co-precipitation method, were applied to methane combustion. Among the various ratios, cobalt nickel mixed oxides having the ratios of Co to Ni of (50:50) and (67:33) demonstrate the highest activity for methane combustion. Structural analysis obtained from X-Ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure (EXAFS) evidently demonstrates that CoNi (50:50) and (67:33) samples consist of NiCo2O4 and NiO phase and, more importantly, NiCo2O4 spinel structure is largely distorted, which is attributed to the insertion of Ni 2+ ions into octahedral sites in Co3O4 spinel structure. Such structural disorder results in the enhanced portion of surface oxygen species, thus leading to the improved reducibility of the catalysts in the low temperature region as evidenced by temperature programmed reduction by hydrogen (H2 TPR) and X-ray Photoelectron Spectroscopy (XPS) O 1s results. They prove that structural disorder in cobalt nickel mixed oxides enhances the catalytic performance for methane combustion. Thus, it is concluded that a strong relationship between structural property and activity in cobalt nickel mixed oxide for methane combustion exists and, more importantly, distorted NiCo2O4 spinel structure is found to be an active site for methane combustion.

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Influence of metal oxides on the performance of Pd/Al2O3 catalysts for methane combustion under lean-fuel conditions

Cited by 64 publications

References 51 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

An Experimental and Kinetic Modelling Study for Methane Oxidation over Pd-based Catalyst: Inhibition by Water

Effect of Co/Ni ratios in cobalt nickel mixed oxide catalysts on methane combustion

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