Structure of defects in γ-irradiated ZSM-5 and Y zeolites: an e.s.r. study

Wichterlová, Blanka; Nováková, J.; Prášil, Z.

doi:10.1016/s0144-2449(88)80076-9

Cited by 16 publications

(16 citation statements)

References 6 publications

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“…2e and Supplementary Table 3 ). Saturation of the EPR signal 25 of TaAlS-1 sample by increasing the microwave power from 7 to 70 mW revealed the appearance of a characteristic signal for Al–O • –Si sites 26 (Fig. 2e ), which is also confirmed by the Pulse HYSCORE spectroscopy (HYSCORE = hyperfine sub-level correlation; Supplementary Note 1 EPR spectroscopy, Supplementary Fig.…”

Section: Resultsmentioning

confidence: 52%

Control of zeolite microenvironment for propene synthesis from methanol

et al. 2021

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Optimising the balance between propene selectivity, propene/ethene ratio and catalytic stability and unravelling the explicit mechanism on formation of the first carbon–carbon bond are challenging goals of great importance in state-of-the-art methanol-to-olefin (MTO) research. We report a strategy to finely control the nature of active sites within the pores of commercial MFI-zeolites by incorporating tantalum(V) and aluminium(III) centres into the framework. The resultant TaAlS-1 zeolite exhibits simultaneously remarkable propene selectivity (51%), propene/ethene ratio (8.3) and catalytic stability (>50 h) at full methanol conversion. In situ synchrotron X-ray powder diffraction, X-ray absorption spectroscopy and inelastic neutron scattering coupled with DFT calculations reveal that the first carbon–carbon bond is formed between an activated methanol molecule and a trimethyloxonium intermediate. The unprecedented cooperativity between tantalum(V) and Brønsted acid sites creates an optimal microenvironment for efficient conversion of methanol and thus greatly promotes the application of zeolites in the sustainable manufacturing of light olefins.

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Section: Resultsmentioning

confidence: 52%

Control of zeolite microenvironment for propene synthesis from methanol

et al. 2021

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“…The hyperfine coupling constant (0.0023 cm -1 ) for signal B is considerably smaller than the coupling constant associated with signal C which is assigned to Nb(IV) (see below). Moreover, the measured g value for signal B is comparable to that of a hole center which is mainly localized on an oxygen in alkali metal silicate glasses and zeolite systems. , …”

Section: Resultsmentioning

confidence: 76%

Synthesis of Niobium Silicate Molecular Sieves of the MFI Structure: Evidence for Framework Incorporation of the Niobium Ion

Prakash

Kevan

1998

J. Am. Chem. Soc.

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A new electron spin resonance (ESR) method to identify incorporation of transition metals into the framework of zeolite molecular sieves is reported. A novel niobium silicate molecular sieve of MFI topology, designated here as NbS-1, is synthesized hydrothermally and characterized by ESR and other physical methods such as X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, electron microprobe analysis, surface area measurements, and 29Si MAS NMR, UV−visible, FTIR, and Raman spectroscopies. Substitution of niobium into the framework has been established by these various methods. γ-Irradiation of activated NbS-1 shows by ESR two radiation-induced hole centers (V centers) located on Si−O−Si and Nb−O−Si units of the framework. The latter can be identified through a 10-line hyperfine structure from 93Nb (I = 9/2, 100% abundance) and provides convincing evidence for the incorporation of Nb into the silica framework. Nb(IV) ions are also formed as a consequence of radiation-induced reduction of Nb(V) associated with isolated tetrahedral NbO4 units and exhibit an axially symmetric ESR signal with a 10-line hyperfine structure due to 93Nb. Silicalite-1, on the other hand, shows radiation-induced hole centers located only on Si−O−Si units.

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“…A second narrow signal with hyperfine structure observed in the spectra of γ-irradiated HZSM-5 and NbAlS-1 (Fig. 1i, Supplementary Table 2), arises from an electron hole defect on a framework oxygen atom in an Al-O  -Si site 37 , where the structure arises from hyperfine coupling with the 27 Al nucleus (I = 5/2; 100% natural abundance). In γ-irradiated NbS-1, a sharp signal is observed, but the hyperfine structure is lost, consistent with the absence of Al(III).…”

Section: Synthesis and Characterisationmentioning

confidence: 99%

Quantitative production of butenes from biomass-derived γ-valerolactone catalysed by hetero-atomic MFI zeolite

et al. 2019

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If citing, it is advised that you check and use the publisher's definitive version. General rights Copyright and moral rights for the publications made accessible in the Research Explorer are retained by the Efficient production of light olefins from renewable biomass is a vital and challenging target to achieve future sustainable chemical processes. Here we report a hetero-atomic MFI-type zeolite (NbAlS-1), over which aqueous solutions of γ-valerolactone (GVL), obtained from biomass-derived carbohydrates, can be quantitatively converted to butenes with a yield of >99% at ambient pressure under continuous flow conditions. NbAlS-1 incorporates simultaneously niobium(V) and aluminium(III) centres into the framework and thus has a desirable distribution of Lewis and Brønsted acid sites with optimal strength. Synchrotron X-ray diffraction and absorption spectroscopy show that there is cooperativity between Nb(V) and Brønsted acid sites on confined adsorption of GVL, while the catalytic mechanism for conversion of confined GVL to butenes is revealed by in situ inelastic neutron scattering, coupled with modelling. This study offers a prospect for the sustainable production of butene as a platform chemical for the manufacture of renewable materials. Approximately 400 million tonnes of light olefins (ethene, propene and butenes) are produced each year for polymer, chemical and pharmaceutical industries 1-6. State-of-the-art processes are based on stream cracking of naphtha and thus critically rely on fossil fuels, possessing significant environmental impacts 1. Catalytic production of light olefins from renewable plant biomass is a highly promising target 7 , and many processes have been developed to bridge future gaps in the supply of commodity chemicals from biomass 8-11. In particular, biomass-derived γ-valerolactone (GVL), obtained from agricultural waste via low-cost, high-yield commercial processes (production scale at 27 tonnes in 2018), has been identified as a sustainable resource to produce butenes 12 , which, through well-established petroleum processes, can be readily transformed to a wide spectrum of petrochemicals, such as propene 2,13 , 1,3-butadiene 14 , aromatics 15 , liquid fuels 2,9 , polyethylene 2,16 and polybutene 2,17. In this respect, development of efficient catalytic processes to convert GVL to butenes is of vital importance. This conversion involves the ring-opening and decarboxylation reactions catalysed over solid acids, and amorphous SiO2/Al2O3, ZSM-5, La/ZSM-5, Ni2P/MCM-41, Zn-AlPO-5 and Pd/Nb2O5 have been studied 9,15,18-24. Using a 30 wt% GVL feedstock at 375 ºC and atmospheric pressure, a butene yield of 75% has been achieved over the SiO2/Al2O3 catalyst 9. Commercial supplies of GVL from biorefineries are aqueous solutions with GVL concentrations between 20-40 wt% 15 ; however, the water in the reaction can partially or completely deactivate solid-acid catalysts by coordinating to the acid sites and forming acid-base adducts 25,26. Thus, the design of an efficient, yet water-tolerant ca...

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Structure of defects in γ-irradiated ZSM-5 and Y zeolites: an e.s.r. study

Cited by 16 publications

References 6 publications

Control of zeolite microenvironment for propene synthesis from methanol

Control of zeolite microenvironment for propene synthesis from methanol

Synthesis of Niobium Silicate Molecular Sieves of the MFI Structure: Evidence for Framework Incorporation of the Niobium Ion

Quantitative production of butenes from biomass-derived γ-valerolactone catalysed by hetero-atomic MFI zeolite

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