An examination of acid sites in H-LTA zeolites

Kresnawahjuesa, Oferi; Heussner, R; Lee, C.-C; Kuehl, G. H.; Gorte, Raymond J.

doi:10.1016/s0926-860x(99)00549-9

Cited by 12 publications

(4 citation statements)

References 18 publications

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“…The amount of either propene or ammonia released from n ‐propylamine decomposition is directly related to the amount of Brønsted acid sites [49] . The formation of propene (Figure 4) further confirms the occurrence of Brønsted acid sites on all catalysts as expected.…”

Section: Resultssupporting

confidence: 78%

“…[48] The amount of either propene or ammonia released from npropylamine decomposition is directly related to the amount of Brønsted acid sites. [49] The formation of propene (Figure 4) further confirms the occurrence of Brønsted acid sites on all catalysts as expected. Commercial NbOPO 4 is the one retaining the highest density of such sites, despite the larger concentration determined for Nb 2 O 5 as collected in Table 1.…”

Section: Chemcatchemsupporting

confidence: 78%

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Hydrolysis of Furfuryl Alcohol to Angelica Lactones and Levulinic Acid over Nb‐based Catalysts

et al. 2023

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Levulinic acid and angelica lactones are important building blocks obtained from hemicellulose. This process comprises multiple chemical reactions at which furfuryl alcohol is an intermediate, but only few studies have investigated its hydrolysis. This work studied the role played by the nature of acid sites and the impact of their strength and amount on furfuryl alcohol hydrolysis over Nb2O5 and NbOPO4. It was disclosed that production of levulinic acid is a two‐step cascade reaction at which angelica lactones are intermediates. These two hydrolysis steps were catalyzed by Brønsted acid sites with no contribution from Lewis centers. Brønsted acidity of Nb2O5 presented no activity while phosphate moieties on NbOPO4 were effective. Mixtures of organic solvent and water hindered side reactions, improving selectivity to valued bioproducts. 1,4‐dioxane was the most suitable organic solvent. This study shows that selectivity of 96 % of levulinic acid and angelica lactones can be accomplished over NbOPO4.

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Section: Resultssupporting

confidence: 78%

Section: Chemcatchemsupporting

confidence: 78%

Hydrolysis of Furfuryl Alcohol to Angelica Lactones and Levulinic Acid over Nb‐based Catalysts

et al. 2023

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“…Desorption of trimethylamine from zeolite was unexpected, but it was found earlier [11] that isopropylamine, which is of similar size, was slowly adsorbed by a high-silica LTA zeolite above about 150°C. The kinetic diameter [9] of isobutene, also of similar size, is 0.50 nm, and it is not surprising that trimethylamine can exit through the 8-member rings at elevated temperature.…”

Section: Natma-mentioning

confidence: 94%

Removal of tetramethylammonium cations from zeolites

Kresnawahjuesa

Olson

Gorte

et al. 2002

Microporous and Mesoporous Materials

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Zeolite α (high-silica LTA), a potential shape-selective catalyst, is synthesized in the presence of tetramethylammonium (TMA) ions. Since TMA + ions are incapable of forming olefins at low temperature, temperatures in excess of 500ºC are required to thermally decompose them and burn off the carbonaceous deposits, frequently causing damage to the structure. In this paper, the thermal decomposition of zeolitic TMA + ions is investigated. This work led to a less severe method for removing TMA + ions by stepwise reaction with ammonia at low temperatures. TMA + ions located in the supercage can easily be removed at a temperature as low as 250ºC, generating mono-and dimethylamine. Sodalite cage TMA + ions require a temperature of not more than 400ºC to be degraded. Although this treatment raises the Si/Al ratio somewhat, damage to the structure is minimal. Since the size of the zeolitic pores defines the type of molecules capable of escaping from the zeolite cavities, decomposition of TMA + ions in NaTMA-Y and NaTMA-high-silica sodalite have been included for comparison. to be degraded. Although this treatment raises the Si/Al ratio somewhat, damage to the structure is minimal. Since the size of the zeolitic pores defines the type of molecules capable of escaping from the zeolite cavities, decomposition of TMA + ions in NaTMA-Y and NaTMA-high-silica sodalite have been included for comparison.

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“…TPD-TGA measurements with n -propylamine on the H−CHA, shown in Figure , indicated that the Brønsted-site density of the sample was ∼700 μmol/g, which is somewhat less than the bulk Al content of 830 μmol/g. The determination of Brønsted-site density using n -propylamine on small-pore zeolites, for which the details of the adsorption procedure are described in more detail elsewhere, , rely on the fact that n -propylamine molecules that are protonated by the Brønsted-acid sites decompose to propene and ammonia in a narrow temperature region, between 625 and 700 K, via a reaction similar to the Hoffman elimination reaction . All of the molecules desorbing below 500 K leave the sample unreacted.…”

Section: Methodsmentioning

confidence: 99%

Molecular Motions of Hydrogen Bonded CH₃CN in the Zeolite Chabazite: Comparison of First-Principles Molecular Dynamics Simulations with Results from ¹H, ²H, and ¹³C NMR

et al. 2000

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Density functional theory calculations with periodic boundary conditions, Car-Parrinello simulations, and multinuclear solid-state NMR experiments at temperatures in the range 77 to 450 K, have been performed to probe the structure and motion of acetonitrile adsorbed at an isolated Brønsted-acid site in chabazite. The 1:1 stoichiometric acetonitrile adsorption complex is hydrogen-bonded to the acid site, and two minima have been found for the position of adsorbed acetonitrile on a proton associated with a single oxygen atom in the zeolite lattice. In agreement with experiment, the results of the Car-Parrinello simulations indicate a free rotation of the methyl group protons about the acetonitrile molecular axis, as well as a motion of this axis that can be described as a two-dimensional libration about the hydrogen bond. The details and temperature dependence of the distributions describing the librational amplitudes as a function of temperature derived from the simulations are, however, not in agreement with experiment. Whereas the experimental distributions reach a limiting value at 300 K, the amplitudes continuously increase in the simulations. The reasons for this are briefly discussed.

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An examination of acid sites in H-LTA zeolites

Cited by 12 publications

References 18 publications

Hydrolysis of Furfuryl Alcohol to Angelica Lactones and Levulinic Acid over Nb‐based Catalysts

Hydrolysis of Furfuryl Alcohol to Angelica Lactones and Levulinic Acid over Nb‐based Catalysts

Removal of tetramethylammonium cations from zeolites

Molecular Motions of Hydrogen Bonded CH₃CN in the Zeolite Chabazite: Comparison of First-Principles Molecular Dynamics Simulations with Results from ¹H, ²H, and ¹³C NMR

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An examination of acid sites in H-LTA zeolites

Cited by 12 publications

References 18 publications

Hydrolysis of Furfuryl Alcohol to Angelica Lactones and Levulinic Acid over Nb‐based Catalysts

Hydrolysis of Furfuryl Alcohol to Angelica Lactones and Levulinic Acid over Nb‐based Catalysts

Removal of tetramethylammonium cations from zeolites

Molecular Motions of Hydrogen Bonded CH3CN in the Zeolite Chabazite: Comparison of First-Principles Molecular Dynamics Simulations with Results from 1H, 2H, and 13C NMR

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Molecular Motions of Hydrogen Bonded CH₃CN in the Zeolite Chabazite: Comparison of First-Principles Molecular Dynamics Simulations with Results from ¹H, ²H, and ¹³C NMR