Proton magic angle spinning nuclear magnetic resonance and temperature programmed desorption studies of ammonia on the acidity of the framework hydroxyl groups in the zeolite H-ZSM-5 and in H-boralite

Scholle, K. F. M. G. J.; Kentgens, A.P.M.; Veeman, W. S.; Frenken, P.; Velden, G. P. M. Van der

doi:10.1021/j150645a003

Cited by 88 publications

(7 citation statements)

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“…Regardless of the type of heteroatoms (Al or B), a 1 H NMR spectrum would show the presence of mainly two classes of hydroxyl groups: bridging hydroxyls that are responsible for the Brønsted acid sites and isolated SiOH groups. It is also known that the weak acid sites of borosilicate zeolites is closely related to low values of isotropic chemical shifts (2−3 ppm) of the possible bridging hydroxyl groups in the NMR spectra. , Unlike aluminosilicate zeolites, the proton form of borosilicate zeolites undergoes B[4] to B[3] transformation upon dehydration, which most likely precludes the existence of the bridging hydroxyl groups (B−O(H + )−Si) around B[3] units (see Scheme ). In addition, B[4] units that are still present even after dehydration should be most likely charge compensated by Na ions, not H + .…”

Section: Resultsmentioning

confidence: 99%

Boron Sites in Borosilicate Zeolites at Various Stages of Hydration Studied by Solid State NMR Spectroscopy

2004

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The local structures of framework boron atoms in borosilicate zeolites B-β, B-SSZ-33 and B-SSZ-42 have been studied in the course of hydration/dehydration by employing solid-state NMR methods. In particular, characterization of trigonal boron sites has been studied in great detail. 11 B MAS NMR spectra showed that boron trigonally coordinated to the framework (B(OSi) 3 , denoted as B[3]) can be readily transformed to a defective trigonal boron site (B(OSi) 2 (OH), denoted as B[3]-I) as a result of hydration. The presence of B[3]-I sites was proven by utilizing a number of different NMR methods including 11 B MAS NMR at two different fields (11.7 and 19.6 T), 11 B MQMAS, 11 B CPMAS, and 11 B 2D HETCOR experiments. The B[3]-I species can be converted into B[3] upon dehydroxylation, but its presence can also be sustained even after very high-temperature treatment (at least up to 500 °C). The formation of deboronated species, B(OH) 3 , in distorted form was detected even under a mild hydration treatment. HETCOR NMR revealed that hydroxyl protons with chemical shifts at 2.4 and 3.3 ppm in 1 H NMR are correlated with B[3] and B[3]-I sites, respectively. The presence of a new hydroxyl proton at 3.8 ppm in 1 H NMR that showed selective correlation with B[3]-I in HETCOR NMR was also identified.

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Section: Resultsmentioning

confidence: 99%

Boron Sites in Borosilicate Zeolites at Various Stages of Hydration Studied by Solid State NMR Spectroscopy

2004

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“…5 and 6 and Table 2 are consistent with previous works (ref. 16,21,32,33,34). Some striking features can be summarized as follows Framework Al results in strong acidity with the corresponding hydroxyl group band at ca 3605 cm (ref.…”

Section: Characterizationmentioning

confidence: 99%

“…Acidity induced by lattice boron was shown to be much weaker than that due to lattice aluminum on the basis of thermoprogrammed desorption of ammonia (TPDA) and proton NMR (ref. 16). Controversy still exists about catalytic properties of boron pentasil zeolites.…”

Section: Introductionmentioning

confidence: 99%

Catalytic and acidic properties of boron pentasil zeolites

Coudurier¹,

Védrine²

1986

Pure and Applied Chemistry

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Pentasil-type zeolite with boron isomorphously substituted for silicon in the pentasil zeolite framework and aluminum pentasil (ZSM-5 type) zeolite impregnated with a boron compound have been prepared and studied. Lattice boron is shown to present trigonal or tetrahedral environment depending upon ligand adsorbates and to induce a weak acid strength and subsequently negligible catalytic activity for acidic-type reactions such as methanol conversion to hydrocarbons, toluene alkylation with methanol and toluene disproportionation. Some activity was observed only if lattice aluminum was present or if aluminum based binder was used. Lattice boron was shown not to modify appreciably shape selectivity.Boron compound impregnated on aluminum pentasil sample was shown to decrease the acidity and subsequently the catalytic activity for acid type reactions but to sharply enhance shape selectivity, i.e. the yield in the less bulky para isomers of aromatics with respect to the other isomers.Boron of the impregnated compound (H3B03) was shown to partly isomorphously substitute for Si or Al upon calcination at 773 K while calcination at 1073 K results in the partial formation of a glassy borosilicate compound at the surface of the zeolite particles. These findings are discussed in light of binder-zeolite interactions.

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“…IR OH stretching vibrations of protons at framework Al and B have been observed at ∼3600 and ∼3700 cm –1 , ,, respectively, but have not been directly quantified to our knowledge in boroaluminosilicates, which would require independent molar extinction coefficients for the two OH groups. Temperature-programmed desorption (TPD) of bases often results in a multitude of desorption features, as observed for ammonia desorption and attributed to acid strength differences between protons compensating framework B and Al. ,,, Yet, ambiguities in interpreting the position of desorption features on the basis of binding strength exist because of convoluting effects of molecular readsorption and diffusion phenomena during egress from microporous voids. , Gorte and co-workers have shown that alkylamine titrants ( t -butylamine, i -propylamine) undergo Hoffman elimination to form ammonia and the corresponding alkene at protons associated with framework Al, but desorb intact from OH groups formed from framework B, , suggesting that such methods could distinguish framework Al and B.…”

Section: Introductionmentioning

confidence: 99%

Ammonia Titration Methods To Quantify Brønsted Acid Sites in Zeolites Substituted with Aluminum and Boron Heteroatoms

Kester

Miller

Gounder

2018

Ind. Eng. Chem. Res.

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Ammonia titration methods were developed to discriminate and quantify Brønsted acid sites of different strength that compensate aluminum and boron heteroatoms incorporated within zeolite frameworks. Borosilicate and boroaluminosilicate MFI zeolites (B-Al-MFI) were synthesized with different Al contents and crystallite sizes, which are typically correlated structural properties in aluminosilicates synthesized hydrothermally, but independently varied here by incorporating boron as a second framework heteroatom and using ethylenediamine as a structure directing agent. Temperature-programmed desorption (TPD) of ammonia from B-Al-MFI samples saturated via liquid-phase NH4NO3 ion exchange resulted in quantifying the total number of Al and B heteroatoms. In contrast, TPD performed after NH4-form B-Al-MFI samples were purged in flowing helium (433 K), or after gas-phase NH3 adsorption (433 K) onto H-form B-Al-MFI samples, quantified only protons charge-compensating framework Al heteroatoms. Turnover rates for methanol dehydration to dimethyl ether, when measured in zero-order kinetic regimes that are sensitive predominantly to Brønsted acid strength, are dependent only on the number of protons compensating framework Al atoms in B-Al-MFI zeolites. The NH3 titration methods developed here are useful in rigorously normalizing turnover rates of Brønsted acid-catalyzed reactions in boroaluminosilicate zeolites, which have been recognized previously to be dependent solely on Al content. The incorporation of B heteroatoms into zeolite frameworks, which generate protons that are essentially unreactive, provides a strategy to influence crystallite sizes independently of Al content, especially relevant in cases where catalytic behavior is influenced by intracrystalline transport phenomena.

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Proton magic angle spinning nuclear magnetic resonance and temperature programmed desorption studies of ammonia on the acidity of the framework hydroxyl groups in the zeolite H-ZSM-5 and in H-boralite

Cited by 88 publications

References 1 publication

Boron Sites in Borosilicate Zeolites at Various Stages of Hydration Studied by Solid State NMR Spectroscopy

Boron Sites in Borosilicate Zeolites at Various Stages of Hydration Studied by Solid State NMR Spectroscopy

Catalytic and acidic properties of boron pentasil zeolites

Ammonia Titration Methods To Quantify Brønsted Acid Sites in Zeolites Substituted with Aluminum and Boron Heteroatoms

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