Towards understanding the improved stability of palladium supported on TS-1 for catalytic combustion

Setiawan, Adi; Friggieri, Jarrod; Hosseiniamoli, Hadi; Kennedy, Eric M.; Dlugogorski, Bogdan Z.; Adesina, Adesoji A.; Stockenhuber, Michael

doi:10.1039/c6cp00319b

Cited by 17 publications

(7 citation statements)

References 41 publications

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“…1b ). The acidic catalysts, Pd/H-MOR and Pd/H-MOR-BE, as well as Pd/Al 2 O 3 , exhibited rapid deactivation within the first 4 h on stream, in agreement with observations by others 14 , 15 , 20 . On the contrary, methane conversion over Pd/Na-MOR improved and the initial 35% difference in conversion increased to 65% after 4 h. Negligible variations in crystallinity (X-ray diffraction, XRD; Supplementary Fig.…”

Section: Resultssupporting

confidence: 90%

Stable complete methane oxidation over palladium based zeolite catalysts

et al. 2018

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Increasing the use of natural gas engines is an important step to reduce the carbon footprint of mobility and power generation sectors. To avoid emissions of unburnt methane and the associated severe greenhouse effect of lean-burn engines, the stability of methane oxidation catalysts against steam-induced sintering at low temperatures (<500 °C) needs to be improved. Here we demonstrate how the combination of catalyst development and improved process control yields a highly efficient solution for complete methane oxidation. We design a material based on palladium and hierarchical zeolite with fully sodium-exchanged acid sites, which improves the support stability and prevents steam-induced palladium sintering under reaction conditions by confining the metal within the zeolite. Repeated short reducing pulses enable the use of a highly active transient state of the catalyst, which in combination with its high stability provides excellent performance without deactivation for over 90 h in the presence of steam.

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Section: Resultssupporting

confidence: 90%

Stable complete methane oxidation over palladium based zeolite catalysts

et al. 2018

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“…Catalytic methane oxidation is important for the utilization of lean-burn natural gas engines since the emission of unburnt methane in the exhaust gas leads to a severe greenhouse effect. , Compared to the conventional catalytic materials like Pd/Al 2 O 3 and Pd/SiO 2 , zeolite-supported palladium catalysts show higher activity for methane combustion at low temperatures (<500 °C) but still suffer from deactivation. − On the one hand, the typical reaction temperature for catalytic methane oxidation results in the sintering of palladium particles on the exterior surface and reducing the number of exposed active sites. On the other hand, the presence of water under the practical reaction conditions causes several problems, such as blocking the active palladium site, facilitating the migration of palladium species, and destroying the framework of low-silica zeolites. − It is also found that the increased acidity of the zeolite enhances the mobility of palladium over the support. , Therefore, searching for a catalyst with low or no palladium mobility and high thermal stability under the reaction conditions is of great importance.…”

Section: Introductionmentioning

confidence: 99%

Stable Palladium Oxide Clusters Encapsulated in Silicalite-1 for Complete Methane Oxidation

Beck

Krumeich

et al. 2021

ACS Catal.

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Zeolite-supported metal catalysts are widely employed in a number of chemical processes, and the stability of the catalytically active species is one of the most critical factors determining the reaction performance. A good example is the Pd/zeolite catalyst, which provides high activity for methane oxidation but deactivates rapidly under the reaction conditions due to palladium nanoparticle sintering. Although coating the metals with thin shells of porous materials is a promising strategy to address the sintering of metals, it is still challenging to fix small metal particles completely inside zeolite crystals. Here, using an aminebased ligand to stabilize palladium during the zeolite synthesis, we realize the exclusive encapsulation of highly dispersed palladium oxide clusters (1.8−2.8 nm) in the microporous channels and voids of the nanosized silicalite-1 crystals. The synthesis conditions of the zeolite-supported catalyst influence the encapsulation degree and the size distribution of metal particles. Thanks to the encapsulation effect of small palladium oxide clusters, together with the inherent properties of silicalite-1 such as low acidity, high hydrophobicity, and high hydrothermal stability, the optimized Pd@silicalite-1 catalyst outperforms the traditional Pd-based catalysts prepared by wetness impregnation, exhibiting both high activity and better stability in the lean methane oxidation reaction.

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“…This change of activation energy after long-term VAM oxidation has also been reported in a previous publication. 26 As the intrinsic data calculation showed, the TOF over the fresh catalyst at a selected temperature of 360 °C decreased from 0.041 to 0.024 s −1 to used catalyst and after reactivation reached 0.031 s −1 (Table 1).…”

Section: Resultsmentioning

confidence: 92%

“…HZSM-5 (Si/Al = 140, Zeolyst International, Kansas, U.S.A.) and palladium(II) nitrate (Sigma-Aldrich) were used as received. Palladium (1 wt %) was loaded on calcined HZSM-5 via the incipient wetness impregnation method, 26 using a Pd(II) nitrate solution (10 wt % in 10 wt % nitric acid). Following impregnation, the sample was dried at 110 °C overnight and calcined at 550 °C for 2 h in air.…”

Section: Methodsmentioning

confidence: 99%

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Understanding Structure–Function Relationships in Zeolite-Supported Pd Catalysts for Oxidation of Ventilation Air Methane

et al. 2018

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Catalytic combustion of ventilation air methane (VAM) is a potential solution for abatement of this greenhouse gas. In this study, we evaluate the combustion of VAM (with methane concentrations below 1%) spanning over 100 h time on stream (TOS) during reaction over a Pd/HZSM-5 catalyst. The aim is to understand the structural changes that lead to catalyst deactivation. We observe the formation of carbonaceous deposits even under oxygen-rich conditions, which are an important contributor to deactivation. X-ray absorption spectroscopic (XAS) investigation shows that, in addition to carbon deposits, the growth of Pd oxide clusters leads to a reduced number of accessible sites and in turn intrinsic activity. STEM-EDS analysis disclosed the presence of the carbonaceous deposit on the surface of the used catalyst, and TGA confirmed the presence of different carbon species on the used catalyst under very lean conditions. Structural changes show that Pd–O/acid–base interactions have a significant influence on the structure of the active site. This assertion is consistent with findings from acid–base characterization experiments. Although the catalyst displayed a high level of stability over the first 10 h of VAM combustion, long-term reaction, in the presence of water vapor, is associated with partial rearrangement of the zeolite, accompanied by a gradual deactivation of the catalyst. This rearrangement is associated with a decrease in surface area and pore volume, which is consistent with the significant changes observed in the Al-X-ray absorption near-edge spectroscopic (XANES) analysis. A comparison of the NH3-TPD of fresh and used Pd/HZSM-5 catalysts shows that the strengths of the acid sites are significantly reduced. This is a consequence of the changing nature of transition metal interaction with the zeolite, which is accompanied by the dealumination of the zeolite support, thereby enhancing Pd agglomeration and the emergence of two low index surface orientation facet planes identified as PdO(101) and PdO(100). A higher turnover frequency (TOF) (0.031 s–1) for reactivated Pd/HZSM-5 after removing all carbonaceous material compared to the TOF (0.024 s–1) for used Pd/HZSM-5 was observed. The catalyst regained 75% of its initial catalytic activity after removing carbonaceous compound from the used catalyst. We propose the formation of a palladium carbonaceous complex manifesting itself in carbonate and a carbonyl group observed in used Pd/HZSM-5. These species act as an important contributor to catalyst deactivation and cause partial reversible deactivation during long-term VAM combustion.

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Towards understanding the improved stability of palladium supported on TS-1 for catalytic combustion

Cited by 17 publications

References 41 publications

Stable complete methane oxidation over palladium based zeolite catalysts

Stable complete methane oxidation over palladium based zeolite catalysts

Stable Palladium Oxide Clusters Encapsulated in Silicalite-1 for Complete Methane Oxidation

Understanding Structure–Function Relationships in Zeolite-Supported Pd Catalysts for Oxidation of Ventilation Air Methane

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