Characterisation and microstructure of Pd and bimetallic Pd–Pt catalysts during methane oxidation

Persson, Katarina; Jansson, Kjell; Järås, Sven

doi:10.1016/j.jcat.2006.10.029

Cited by 135 publications

(80 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Pd-bimetallic catalysts are usually less active than Pd alone [64,[73][74][75] simply because they contain less Pd, the most active metal for CH4 oxidation [20,25]. The lower activity of the bimetallic compared to Pd alone may also be due to the presence of smaller amounts of PdO as a result of alloy formation between Pd and Pt [64], or the transformation of PdO to Pd metal [76].…”

Section: The Use Of Pd-bimetallic Catalysts For Ch 4 Oxidationmentioning

confidence: 99%

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

2015

View full text Add to dashboard Cite

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.

show abstract

Section: The Use Of Pd-bimetallic Catalysts For Ch 4 Oxidationmentioning

confidence: 99%

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

2015

View full text Add to dashboard Cite

show abstract

“…Hence, it is evident that thermal aging leads to particle sintering whereby palladium becomes more oxidized and forms larger crystallites. [10] The stabilization of a diffuse oxide phase due to a partial diffusion of oxidic Rh species into the subsurface of alumina might occur and explains the abnormally high Rh 3d BE value (see Table 1). This explanation is supported by previous investigations.…”

Section: Experimental Catalyst Preparationmentioning

confidence: 99%

XPS investigation of surface changes during thermal aging of Natural Gas Vehicle catalysts: Influence of Rh addition to Pd

Renème

Dhainaut

Trentesaux

et al. 2010

Surface & Interface Analysis

View full text Add to dashboard Cite

This study investigates thermal aging induced effects on the surface properties of model and commercial automotive catalysts for Natural Gas Vehicles, by means of X-ray photoelectron spectroscopy and infrared spectroscopy of chemisorbed CO as a probe molecule for noble metals. Post-combustion catalysts for this application are essentially composed of palladium containing low amounts of rhodium and additives to improve the oxygen storage properties. The aging procedure involved exposing the catalysts to an oxidizing atmosphere containing air and 10 vol.% H 2 O at 980• C for 4 h in order to simulate surface changes which may occur under usual three-way operating conditions. It was found that sintering processes led to a significant loss of Pd concentration on model and commercial catalysts. Regarding Rh, diffusion processes into alumina also take place, which are partially inhibited on model catalysts when Rh interacts with Pd. Greater stabilization of Rh species is suggested on commercial catalysts in the presence of oxygen storage materials.

show abstract

“…The qualitative conversion profiles demonstrated the effects of preparative methodology and chemical structure on the catalytic activities and stabilities as a function of reaction temperature. As can be seen in Figure 9a, in the case of the 5Pd-I sample after the light-off at 250 • C, the catalytic activity started increasing and finally reached a maximum of 85% of conversion of methane at~500 • C. However, with further heating a strong deactivation dip for CH 4 oxidation in the range of 500-750 • C was observed. It was worth noticing that with the 5Pd-I catalyst a complete conversion of methane was never achieved.…”

Section: Catalytic Activitymentioning

confidence: 85%

“…The reaction temperature was then raised to 500 • C at a heating rate of 5 • C min −1 in flowing H 2 . This step was followed by flushing the catalyst bed with 20 mL min −1 Ar for 20 min and then the inert gas was replaced by the required CH 4 /O 2 gases mixture at a total gas pressure of 1 atm with O 2 (5% O 2 /Ar) to CH 4 (5% CH 4 /Ar) v/v ratio of 2. The cooling cycle in the temperature range between 500 • C and 200 • C was then taken at cooling rates of −5 K min −1 .…”

Section: Effect Of Reductive Pretreatment On Catalytic Activitymentioning

confidence: 99%

“…The conventional thermal combustion of methane not only requires very high temperatures (up to 1600 • C) but also results in production of NO x as by-products. Thus the development of effective methane combustion catalysts would have a significant impact on a number of energy-based technologies [4,5]. CH 4 combustion promoted by heterogeneous catalysts would not only utilize the energy of methane at lower operating temperature but would also increase system performance and limit NO x emissions by drastically reducing the required temperatures [6,7].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Active and Stable Methane Oxidation Nano-Catalyst with Highly-Ionized Palladium Species Prepared by Solution Combustion Synthesis

et al. 2018

View full text Add to dashboard Cite

We report on the synthesis and testing of active and stable nano-catalysts for methane oxidation. The nano-catalyst was palladium/ceria supported on alumina prepared via a one-step solution-combustion synthesis (SCS) method. As confirmed by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HTEM), SCS preparative methodology resulted in segregating both Pd and Ce on the surface of the Al 2 O 3 support. Furthermore, HTEM showed that bigger Pd particles (5 nm and more) were surrounded by CeO 2 , resembling a core shell structure, while smaller Pd particles (1 nm and less) were not associated with CeO 2 . The intimate Pd-CeO 2 attachment resulted in insertion of Pd ions into the ceria lattice, and associated with the reduction of Ce 4+ into Ce 3+ ions; consequently, the formation of oxygen vacancies. XPS showed also that Pd had three oxidation states corresponding to Pd 0 , Pd 2+ due to PdO, and highly ionized Pd ions (Pd (2+x)+ ) which might originate from the insertion of Pd ions into the ceria lattice. The formation of intrinsic Ce 3+ ions, highly ionized (Pd 2+ species inserted into the lattice of CeO 2 ) Pd ions (Pd (2+x)+ ) and oxygen vacancies is suggested to play a major role in the unique catalytic activity. The results indicated that the Pd-SCS nano-catalysts were exceptionally more active and stable than conventional catalysts. Under similar reaction conditions, the methane combustion rate over the SCS catalyst was~18 times greater than that of conventional catalysts. Full methane conversions over the SCS catalysts occurred at around 400 • C but were not shown at all with conventional catalysts. In addition, contrary to the conventional catalysts, the SCS catalysts exhibited superior activity with no sign of deactivation in the temperature range between~400 and 800 • C.

show abstract

Characterisation and microstructure of Pd and bimetallic Pd–Pt catalysts during methane oxidation

Cited by 135 publications

References 37 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

XPS investigation of surface changes during thermal aging of Natural Gas Vehicle catalysts: Influence of Rh addition to Pd

Active and Stable Methane Oxidation Nano-Catalyst with Highly-Ionized Palladium Species Prepared by Solution Combustion Synthesis

Contact Info

Product

Resources

About