Mechanisms behind sulfur promoted oxidation of methane

Bounechada, Djamela; Fouladvand, Sheedeh; Kylhammar, Lisa; Pingel, Torben; Olsson, Eva; Skoglundh, Magnus; Gustafson, Johan; Michiel, Marco Di; Newton, Mark A.; Carlsson, Per-Anders

doi:10.1039/c3cp44289f

Cited by 33 publications

(38 citation statements)

References 79 publications

(233 reference statements)

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“…These bands increased in intensity and shifted to higher frequencies with extended SO 2 exposure. The observed shift has been previously reported by several authors [30][31][32], ascribed to either pure frequency shift of a single band caused by the change in the strength of molecular interactions or the combined effect of two overlapping bands that differ in relative intensity. The shift in frequency is observed only after 90 min of sulfur poisoning.…”

Section: Influence Of Sulfur On Different Precious Metal Speciessupporting

confidence: 79%

“…In contrast, ceria-containing catalysts required higher temperatures for sulfur removal compared to other samples, probably caused by a large formation of very stable bulk sulfates during SO 2 poisoning procedure, as reported from DRIFTS measurements. Bounechada et al [32] indeed suggested that the high dynamic oxygen storage capacity (OSC) of ceria-containing materials leads to the diffusion of surface sulfates into the bulk, blocking some pores and inhibiting the access to active sites. Meanwhile, the remaining sulfur species on Ce-containing catalysts certainly affected the NO x stored stability by reducing the amount of NO x released after sulfation.…”

Section: Interpretation Of the Sulfur Poisoning And Regeneration Resultsmentioning

confidence: 99%

“…According to the literature, the bands at 1346 and 1156 cm −1 correspond to surface and bulk sulfates [30,32,49,50], respectively. The surface sulfate can be either formed on Al 2 O 3 and/or ceria sites [29,30,32,34,49], whereas bulk sulfate is mostly associated with ceria sites [32,49]. The 1156 cm −1 band can be also associated with bulk MgSO 4 [48], however, this is not likely since it was not observed for Mg-Al 2 O 3 samples (see Figure 5).…”

Section: Influence Of Sulfur On Ceria Compoundmentioning

confidence: 94%

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Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

2019

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In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NO x trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, which mainly consisted of three compounds: (i) Al 2 O 3 , (ii) Mg/Al 2 O 3 , and (iii) Mg/Ce/Al 2 O 3 mixed with Pt, Pd, and Pt-Pd. A micro flow reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were employed in order to investigate the evolution and stability of the species formed during SO 2 poisoning. The results showed that the addition of palladium and magnesium into the LNT formulation can be beneficial for the catalyst desulfation due mainly to the ability to release the sulfur trapped at relatively low temperatures. This was especially evident for Pd/Mg/Al 2 O 3 model catalyst, which demonstrated an efficient LNT desulfation with low H 2 consumption. In contrast, the addition of ceria was found to increase the formation of bulk sulfate species during SO 2 poisoning, which requires higher temperatures for the sulfur removal. The noble metal nature was also observed to play an important role on the SO x storage and release properties. Monometallic Pd-based catalysts exhibited the formation of surface palladium sulfate species during SO 2 exposure, whereas Pt-Pd bimetallic formulations presented higher stability of the sulfur species formed compared to the corresponding Pt-and Pd-monometallic samples.Catalysts 2019, 9, 492 2 of 18 urea [4]. Nevertheless, the LNT system is highly susceptible to sulfur, and its performance can be severely affected as NO x storage sites are blocked by sulfur [5][6][7]. Sulfates formed on the NO x storage sites have higher thermal stability than nitrates and nitrites and, therefore, their decomposition needs very high temperatures and alternating rich/lean exhaust mixtures [8,9]. This does not only lead to higher fuel consumption due to regular desulfation events, but may also cause structural deactivation of the catalyst, such as sintering of precious metals and the formation of mixed oxides (e.g., BaAl 2 O 4 for the reaction between Al 2 O 3 and BaO at high temperatures), affecting the overall NO x storage and reduction activity of the catalyst [10][11][12].Therefore, the sulfur tolerance of modern LNT catalysts should be improved by replacing the NO x trapping material with a component with lower affinity towards sulfation, and with enhanced desorption of sulfur species during regeneration. Barium is frequently employed as a storage material because of its high thermal stability, however, it is responsible for the major LNT catalyst deterioration due to its high affinity for sulfation [13]. Ji et al. [14] studied the incorporation of ceria to Ba-based LNT catalysts and determined to provide a positive impact on LNT performance in the presence of sulfur. Ceria was found to enhance sulfur tolerance of the LNT catalyst by storing sulfur species, which mitigates the sulfation o...

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Section: Influence Of Sulfur On Different Precious Metal Speciessupporting

confidence: 79%

Section: Interpretation Of the Sulfur Poisoning And Regeneration Resultsmentioning

confidence: 99%

Section: Influence Of Sulfur On Ceria Compoundmentioning

confidence: 94%

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Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

2019

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“…The details on the preparation and characterisation of the Pt/SiO 2 sample can be found elsewhere 16 and thus we give only a brief description here. Silica powder (Kromasil Silica KR-300-10, Akzo…”

Section: Experimental and Theoretical Methods Sample Preparation And mentioning

confidence: 99%

Vibrational Study of SO_x Adsorption on Pt/SiO₂

et al. 2014

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The formation of ad-SO x species on Pt/SiO 2 upon exposure to SO 2 in concentrations ranging from 10 to 50 ppm at between 200 and 400 C has been studied by in situ diffuse reflectance infrared Fourier transformed spectroscopy. In parallel, first-principles calculations have been carried out to consolidate the experimental interpretations. It was found that sulfate species form on the silica surface with a concomitant removal/rearrangement of silanol groups. Formation of ad-SO x species occurs only after SO 2 oxidation to SO 3 on the platinum surface. Thus SO 2 oxidation to SO 3 is the first step in the SO x adsorption process, followed by spillover of SO 3 to the oxide and, finally, the formation of sulfate species on the hydroxyl positions on the oxide. The sulfate formation is influenced by both temperature and SO 2 concentration.

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“…The samples are from here referred to as Pt/Al, Pt/AlCe and Pt/Ce, respectively. Transient activity tests were performed with monolith samples in a continuous gas-flow reactor, which has been described in detail elsewhere [21]. The monolith samples were prepared by coating 200 mg of the respective powder catalyst onto cordierite monolith substrates (L=15 mm, ?=12 mm) as described in reference [20].…”

Section: Methodsmentioning

confidence: 99%

Unsteady-state operation of supported platinum catalysts for high conversion of methane

Fouladvand

Skoglundh

Carlsson

2016

Chemical Engineering Journal

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Total oxidation of methane over model monolith catalysts with platinum supported on alumina, alumina-ceria and ceria has been studied under unsteadystate operation of the feed gas stoichiometry. The general activity for methane oxidation follows the order Pt/alumina < Pt/alumina-ceria < Pt/ceria. Thanks to high catalytic activity at the gas composition switches, increased cycling frequency between oxygen excess and oxygen free conditions increases the average methane conversion significantly from 11 to 58% for Pt/alumina and from 25 to 87% for Pt/alumina-ceria. The corresponding stationary methane conversion is 10 and 19%, respectively. The underlying reason for the enhanced catalytic activity is likely twofold namely that periods with detrimentally high coverage of either oxygen or carbon are shortened and that the transients induce a highly active (chemical) state of the catalyst, thus, facilitating high average conversion of methane.

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Mechanisms behind sulfur promoted oxidation of methane

Cited by 33 publications

References 79 publications

Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

Vibrational Study of SO_x Adsorption on Pt/SiO₂

Unsteady-state operation of supported platinum catalysts for high conversion of methane

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Mechanisms behind sulfur promoted oxidation of methane

Cited by 33 publications

References 79 publications

Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

Vibrational Study of SOx Adsorption on Pt/SiO2

Unsteady-state operation of supported platinum catalysts for high conversion of methane

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Vibrational Study of SO_x Adsorption on Pt/SiO₂