Solid-state transformation of SAPO-37 molecular sieve above 1100 K

Derewinski, Miroslav; Peltre, M.J.; Briend, M.; Barthomeuf, D.; Man, Pascal P.

doi:10.1039/ft9938901823

Cited by 36 publications

(18 citation statements)

References 12 publications

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“…[20,21] Importantly, at high temperatures the H-SAPO framework can be (locally) separated into silicon domains and the AlPO 4 phase. [20,22] This transformation, which can take place during the oxidative treatments applied to regenerate the MTH catalysts, might induce significant changes in their physicochemical properties. More specifically, it has been reported that the formation of silicon islands leads to a reduction in the number of acid sites available for the MTH reaction and increases the acid strength of the Si-OH-Al species located at boundaries of the H-SAPO and the silicon island phases.…”

Section: Physicochemical Changes By Applying a Severe Hydrothermal Trmentioning

confidence: 99%

“…This observation is in line with previous studies performed on H-SAPO-34 materials and indicates a redistribution of silicon atoms occurring at high steaming temperatures. [22,27] Complementary to the 29 Si MAS NMR experiments, 27 Al MAS NMR measurements on the SAPO-34-C and SAPO-34-S molecular sieves were performed. As presented in Figure 3 b, the spectrum of SAPO-34-C is characterized by peaks at around d = 60-50 and 0 ppm, indicative for the presence of a mixture of 4and 6-fold aluminum coordinated species, respectively.…”

Section: Physicochemical Changes By Applying a Severe Hydrothermal Trmentioning

confidence: 99%

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X‐Ray Imaging of SAPO‐34 Molecular Sieves at the Nanoscale: Influence of Steaming on the Methanol‐to‐Hydrocarbons Reaction

et al. 2013

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The effect of a severe steaming treatment on the physicochemical properties and catalytic performance of H‐SAPO‐34 molecular sieves during the methanol‐to‐hydrocarbons (MTH) reaction has been investigated with a combination of scanning transmission X‐ray microscopy (STXM), catalytic testing, and bulk characterization techniques, including ammonia temperature programmed desorption and 27Al and 29Si magic angle spinning nuclear magnetic resonance. For this purpose, two samples, namely a calcined and a steamed H‐SAPO‐34 catalyst powder, have been compared. It has been found that calcined H‐SAPO‐34 displays a high selectivity towards light olefins, yet shows a poor stability as compared to a zeolite H‐ZSM‐5 catalyst. Moreover, in situ STXM at the carbon K‐edge during the MTH reaction allows construction of nanoscale chemical maps of the hydrocarbon species formed within the H‐SAPO‐34 aggregates as a function of reaction time and steam post‐treatment. It was found that there is an initial preferential formation of coke precursor species within the core of the H‐SAPO‐34 aggregates. For longer times on stream the formation of the coke precursor species is extended to the outer regions, progressively filling the entire H‐SAPO‐34 catalyst particle. In contrast, the hydrothermally treated H‐SAPO‐34 showed similar reaction selectivity, but decreased activity and catalyst stability with respect to its calcined counterpart. These variations in MTH performance are related to a faster and more homogeneous formation of coke precursor species filling up the entire steamed H‐SAPO‐34 catalyst particle. Finally, the chemical imaging capabilities of the STXM method at the Al and Si K‐edge are illustrated by visualizing the silicon islands at the nanoscale before and after steaming H‐SAPO‐34.

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Section: Physicochemical Changes By Applying a Severe Hydrothermal Trmentioning

confidence: 99%

Section: Physicochemical Changes By Applying a Severe Hydrothermal Trmentioning

confidence: 99%

X‐Ray Imaging of SAPO‐34 Molecular Sieves at the Nanoscale: Influence of Steaming on the Methanol‐to‐Hydrocarbons Reaction

et al. 2013

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“…Presence of such lattice has never been previously observed or stated for SSZ-39 (or isostructural zeolites) although isostructural zeolite SAPO-18, for example, has been studied with electron microscopy [28]; we note that the presence of incommensurate lattice may potentially be one of the factors contributing to such high stability of this material, because such lattice modulations have not been observed for SSZ-13 material (built of the same structural units and having essentially the same crystallographic density as SSZ-39): this point needs further investigation. However, as has been previously demonstrated in the pioneering studies by Derewinski, Barthomeuf and co-workers [29][30][31][32], the enhanced thermal stability of the larger zeolite crystals compared with nanosized analogues is the consequence of the absence of highindex facets and presence of mostly low-index facets having lower surface energy and thus increased thermal stability. It was also demonstrated that structure of another SAPO material i.e.…”

Section: Pna Performance Of Hydrothermally Aged Pd/ssz-39 Materialsmentioning

confidence: 77%

The Superior Hydrothermal Stability of Pd/SSZ-39 in Low Temperature Passive NOx Adsorption (PNA) and Methane Combustion

Khivantsev¹,

Jaegers²,

Kovařík³

et al. 2020

Preprint

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We successfully synthesized uniform SSZ-39 with an average crystal size of about a micron. Pd (0.7 - 3 wt%) was supported on SSZ-39 with Si/Al ratio ~12. The as-synthesized materials were characterized by FTIR, XRD, Helium Ion Microscopy, HAADF-STEM imaging, 27Al, 29Si and H solid state NMR spectroscopic techniques. <br>FTIR studies with CO and NO probe molecules reveal that the 0.7 wt% Pd/SSZ-39 material with Si/Al ~12 has the majority of Pd dispersed atomically as isolated Pd(II) and Pd(II)-OH centers, and thus can be used as a low-temperature passive NOx adsorber. Pd(II)-NO, Pd(II)(OH)(NO) and Pd(II)(CO)(NO) complexes form during PNA in this material. We compare this PNA material directly with the Pd/SSZ-13 system (with Si/Al ratio ~12) and show its superior hydrothermal stability. Remarkably, Pd/SSZ-39 with Si/Al ratio ~12 survives hydrothermal aging up to 815 ºC in 10% H2O/Air vapor for 16 hours without significant loss in activity. The SSZ-39 crystal structure remains intact during hydrothermal aging up to 1,000 ºC as we elucidate it with XRD and HAADF-STEM imaging/EDS mapping. However, changes to the framework during such harsh hydrothermal treatment significantly change the NOx release profiles during PNA as evidenced by high-field 27Al NMR on fresh and aged Pd/SSZ-39 samples as well as PNA performance measurements. <br>Besides PNA application, these hydrothermally very stable materials (3 wt% Pd on SSZ-39 with Si/Al ratio ~12) can be used as a robust methane combustion catalyst under industrially relevant conditions (GHSV~600,000hr-1). This catalyst shows minimal deactivation after both harsh hydrothermal aging at 750 and 800 ºC, and prolonged time on stream (105 hrs) at 425 ⁰C. In contrast, both 3wt% Pd/alumina and 3wt% SSZ-13 supported samples lose a significant portion of their activity.<br>

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“…The combination of the SM2 and SM3 mechanisms leads to the formation of silicon aggregates or "silicon islands" [8]. Silicon islands are formed when at least two adjacent T sites are occupied by silicon [9,10], [11].…”

Section: Scopementioning

confidence: 99%