Characterization and study on the thermal aging behavior of palladium–alumina catalysts

Vedyagin, Aleksey A.; Volodin, Alexander M.; Kenzhin, Roman M.; Stoyanovskii, Vladimir O.; Rogov, Vladimir A.; Medvedev, Dmitrii A.; Mishakov, Ilya V.

doi:10.1007/s10973-017-6530-y

Cited by 19 publications

(6 citation statements)

References 53 publications

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“…The sintering of active components can hinder the Ce 4+ to Ce 3+ reaction, decreasing the contact between the material and the engine out gases. Similar results have been reported in the literature [22,28]. The interaction of the materials with Ce sharing O atom can be altered due to the sintering of metal particles, leading to the decrease of OSC and catalytic activity of TWC as the catalyst deactivation proceeds [32,33].…”

Section: Three-way Catalysts (Twcs)supporting

confidence: 86%

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First of Its Kind Automotive Catalyst Prepared by Recycled PGMs-Catalytic Performance

Moschovi¹,

Giuliano

Kourtelesis³

et al. 2021

Catalysts

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The production of new automotive catalytic converters requires the increase of the quantity of Platinum Group Metals in order to deal with the strict emission standards that are imposed for vehicles. The use of PGMs coming from the recycling of spent autocatalysts could greatly reduce the cost of catalyst production for the automotive industry. This paper presents the synthesis of novel automotive Three-Way Catalysts (PLTWC, Pd/Rh = 55/5, 60 gPGMs/ft3) and diesel oxidation catalysts (PLDOC, Pt/Pd = 3/1, 110 gPGMs/ft3) from recovered PGMs, without further refinement steps. The catalysts were characterized and evaluated in terms of activity in comparison with benchmark catalysts produced using commercial metal precursors. The small-scale catalytic monoliths were successfully synthesized as evidenced by the characterization of the samples with XRF analysis, optical microscopy, and N2 physisorption. Hydrothermal ageing of the catalysts was performed and led to a significant decrease of the specific surface area of all catalysts (recycled and benchmarks) due to sintering of the support material and metal particles. The TWCs were studied for their activity in CO and unburned hydrocarbon oxidation reactions under a slightly lean environment of the gas mixture (λ > 1) as well as for their ability to reduce NOx under a slightly rich gas mixture (λ < 1). Recycled TWC fresh catalyst presented the best performance amongst the catalysts studied for the abatement of all pollutant gases, and they also showed the highest Oxygen Storage Capacity value. Moreover, comparing the aged samples, the catalyst produced from recycled PGMs presented higher activity than the one synthesized with the use of commercial PGM metal precursors. The results obtained for the DOC catalysts showed that the aged PLDOC catalyst outperformed both the fresh catalyst and the aged DOC catalyst prepared with the use of commercial metal precursors for the oxidation of CO, hydrocarbons, and NO. The latter reveals the effect of the presence of several impurities in the recovered PGMs solutions.

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Section: Three-way Catalysts (Twcs)supporting

confidence: 86%

“…The role of the Zr promoter is to increase the ceria's thermal stability and favor metal dispersion [27]. However, CeO 2 -ZrO 2 has also been found to inactivate in increased temperatures under ageing conditions [28]. Noble metal particles are also subjected to similar processes.…”

Section: Discussionmentioning

confidence: 99%

First of Its Kind Automotive Catalyst Prepared by Recycled PGMs-Catalytic Performance

Moschovi¹,

Giuliano

Kourtelesis³

et al. 2021

Catalysts

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“…Palladium-based catalysts are used since many years as selective heterogeneous catalysts for hydrogenation reactions in different industrial processes, from petrochemical to the synthesis of fine and bulk chemicals and removal of water pollutants. [1][2][3][4][5][6][7][8][9] Since palladium is one of the rarest elements available on earth, the European Community has recently included this metal in the list of raw materials deemed critical in terms of supply risk. 10 Because of this, the control of the synthesis parameters of Pd-based catalysts, such as: metal precursor, activation method, type of support, should be evaluated for tuning the catalysts properties in order to ultimately impact the catalytic performance.…”

Section: Introductionmentioning

confidence: 99%

Anin situXAS study of the activation of precursor-dependent Pd nanoparticles

Lopes

Cerrillo

Palomares

et al. 2018

Phys. Chem. Chem. Phys.

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The activation of precursor-dependent Pd nanoparticles was comprehensively followed by in situ X-ray absorption spectroscopy on two inorganic supports for rationalizing the final catalytic activity. Two series of Pd-based catalysts (7 wt% Pd) were prepared by impregnation of γ-Al2O3 and activated carbon supports varying the metal precursor (Pd(NO3)2, PdCl2 and Pd(OAc)2). The most relevant physicochemical properties of the studied catalysts were determined by several techniques including ICP-OES, XRD, N2 adsorption and XAS. The results indicate that the thermal stability of the metal precursor plays an important role in the size and speciation of the formed Pd nanoparticles after the activation process. The Cl-based precursor, which presents high thermal stability, passes through a PdOxCly mixed phase when submitted to calcination on Pd/Al2O3 and leaves Cl-species after metal reduction on Pd/C (which can be detrimental to catalytic reactions). Differently, Pd(OAc)2 and Pd(NO3)2 promote the formation of larger species due to different precursor decomposition pathways. Ordered PdO is observed even before calcination when Pd(NO3)2 was used as a metallic source, which translates into large nanoparticles after reduction in H2. By using the average coordination numbers of Pd species obtained from EXAFS data of the as-reduced catalysts, a correlation was observed comparing the three precursors: PdCl2 generates smaller nanoparticles than Pd(OAc)2, which in turn generates smaller nanoparticles than Pd(NO3)2, regardless of the support used for catalyst preparation.

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“…Figure 9 a presents diffuse reflectance UV–Vis spectra for the as-prepared Pd/C12A7 and Pd@C12A7 samples. The Pd-O charge transfer bands at 250 nm and the d-d transition bands of Pd 2+ at 450 nm [ 49 , 50 ] in square-planar coordination for PdO clusters on the Al 2 O 3 support with a characteristic band-gap value of ~2.35 eV [ 51 ] are shown with dashed lines. The band-gap energy value for PdO bulk particles is significantly lower and, according to optical transmittance measurements, equal to ~0.8 eV [ 52 ], while electric conductivity measurements have indicated an energy gap value of ~1.5 eV [ 53 ].…”

Section: Resultsmentioning

confidence: 99%

Comparative Study of Pd-Mayenite Catalysts Prepared via Aerogel Approaches

Ilyina

Bedilo

Veselov

et al. 2022

Gels

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Pd-containing catalysts based on highly dispersed aerogel-derived mayenite were prepared via two approaches. The Pd@C12A7 sample was obtained through the addition of Pd nitrate solution to a fresh Ca(OH)2-Al(OH)3 gel. Pd/C12A7 was synthesized through conventional wet impregnation of the aerogel-derived mayenite. The evolution of the textural characteristics of the support (C12A7) depending on the calcination temperature was investigated. Pd-containing samples were explored using transmission electron microscopy and spin probe EPR spectroscopy. Using the latter method, the presence of active oxygen species capable of producing nitroxyl radicals from diphenylamine was observed. The activity of these species and the reproducibility of their redox behavior were studied in three cycles of temperature-programmed reduction in both hydrogen and CO atmospheres. A prompt thermal aging technique was used to access and compare the activity of the samples towards CO oxidation. The state of Pd species before and after the aging procedure was studied via UV–Vis spectroscopy. It was found that the dispersion of PdO was higher in the case of the Pd/C12A7 catalysts compared to the Pd@C12A7 sample. This is why the Pd/C12A7 catalyst demonstrated higher activity in CO oxidation and better reducibility in TPR cycles.

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Characterization and study on the thermal aging behavior of palladium–alumina catalysts

Cited by 19 publications

References 53 publications

First of Its Kind Automotive Catalyst Prepared by Recycled PGMs-Catalytic Performance

First of Its Kind Automotive Catalyst Prepared by Recycled PGMs-Catalytic Performance

Anin situXAS study of the activation of precursor-dependent Pd nanoparticles

Comparative Study of Pd-Mayenite Catalysts Prepared via Aerogel Approaches

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