FTi.r. spectroscopic study of gallium beta

Hegde, S.G.; Abdullah, Rohana; Bhat, R.N.; Ratnasamy, P.

doi:10.1016/0144-2449(92)90160-q

Cited by 20 publications

(5 citation statements)

References 13 publications

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“…10 TS-1 is wellknown for its excellent performance in oxidation reactions. 11 Many experimental studies [12][13][14][15][16] have investigated the structures and acidity of zeolites and the isomorphously substituted zeolites containing different framework atoms. Chu 15 used infrared (IR) spectroscopy and temperature-programmed desorption (TPD) of adsorpted NH 3 to study the acidity of several isomorphously substituited M-ZSM-5 with the increased acid strength: Si-(OH) < B-(OH)-Si , Fe-(OH)-Si < Ga-(OH)-Si < Al-(OH)-Si.…”

Section: Introductionmentioning

confidence: 99%

Brønsted Acidity of Isomorphously Substituted ZSM-5 by B, Al, Ga, and Fe. Density Functional Investigations

Yuan

Wang

et al. 2002

J. Phys. Chem. A

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The Brønsted acidity of isomorphously substituted ZSM-5 by B, Al, Ga, and Fe has been studied at the B3LYP level of density functional theory. On the basis of the calculated proton affinity, natural charge on the acidic proton, and the adsorption energy of NH3, the Brønsted acidity increases in the order: B−(OH)−Si < Fe−(OH)−Si < Ga−(OH)−Si < Al−(OH)−Si, in agreement with the experiment. In both Al and Ga modified clusters, the adsorbed NH3 becomes ammonium (NH4 +) stabilized by two N−H···O hydrogen bonds, while the physisorbed NH3 is stabilized by one N···H−O hydrogen bond in Fe and B substituted clusters. It is also found that NH3 adsorption changes the B coordination sphere.

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Section: Introductionmentioning

confidence: 99%

Brønsted Acidity of Isomorphously Substituted ZSM-5 by B, Al, Ga, and Fe. Density Functional Investigations

Yuan

Wang

et al. 2002

J. Phys. Chem. A

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“…The acidic property of gallosilicate has been investigated by means of the infrared (IR) spectroscopy of surface hydroxide, − the adsorbed pyridine, carbon monoxide , and nitrogen, and the nuclear magnetic resonance of proton ( 1 H NMR), supported by quantum chemical calculations. − These spectroscopic methods mainly deal with the quality of the acid site, but the quantitative measurement is difficult. Traditional indicator and amine titration methods to quantify the acid amount have a disadvantage, because they are confused by the slow diffusion of liquid molecules in the micropore.…”

Section: Introductionmentioning

confidence: 99%

“…The acidic property of gallosilicate has been investigated by means of the infrared (IR) spectroscopy of surface hydroxide, [19][20][21][22] the adsorbed pyridine, 23 carbon monoxide 24,25 and nitrogen, 25 and the nuclear magnetic resonance of proton ( 1 H NMR), 26 supported by quantum chemical calculations. [27][28][29][30] These spectroscopic methods mainly deal with the quality of the acid site, but the quantitative measurement is difficult.…”

Section: Introductionmentioning

confidence: 99%

Acidic Property of MFI-Type Gallosilicate Determined by Temperature-Programmed Desorption of Ammonia

et al. 1998

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Temperature-programmed desorption of ammonia was applied to gallosilicate with MFI structure using the water vapor treatment method to remove the unnecessary low-temperature peak and the curve-fitting method to calculate the acid strength and its distribution based on the thermodynamics. The determined acid amount approximately agreed with the [Ga]-[Na] content in the low gallium content region, showing the stoichiometric generation of one acid site by the substitution of one gallium atom, and stoichiometric neutralization of one acid site by one sodium atom. The acid strength (adsorption heat of ammonia) due to the framework gallium was ca. 130 kJ mol -1 with the small distribution, close to that on the ZSM-5 type aluminosilicate, and was independent of the composition. This shows that the substitution of Al and Ga into the zeolitic crystal generates the similar acid strength, and the acidic strength is mainly determined by the crystal structure. The extraframework gallium on the ion-exchange site, which was readily formed with the gallium content higher than 0.3-0.4 mol kg -1 , generated the additional type of acid site with the higher adsorption heat of ammonia. IntroductionZeolite, which consists of SiO 2 and Al 2 O 3 , has widely been used as a heterogeneous catalyst. 1-6 In place of the aluminum, various kinds of metals can be incorporated into the framework, and the obtained metallosilicates are being considered as novel functionalized materials. 7 Especially, gallosilicate with MFI structure has a remarkable catalytic activity for the conversion of alkane into aromatics. [8][9][10][11][12][13][14][15][16][17][18] Generation of acidity by isomorphous substitution of silicon by gallium is presumed to be the origin of the catalytic functions. Analysis of the acidic property, namely, the number, strength, and nature (Brønsted or Lewis) of the acid sites, is therefore important to interpret the catalytic functions and, moreover, must be important also from the physicochemical viewpoint.The acidic property of gallosilicate has been investigated by means of the infrared (IR) spectroscopy of surface hydroxide, 19-22 the adsorbed pyridine, 23 carbon monoxide 24,25 and nitrogen, 25 and the nuclear magnetic resonance of proton ( 1 H NMR), 26 supported by quantum chemical calculations. 27-30 These spectroscopic methods mainly deal with the quality of the acid site, but the quantitative measurement is difficult. Traditional indicator 31 and amine titration 32 methods to quantify the acid amount have a disadvantage, because they are confused by the slow diffusion of liquid molecules in the micropore. Test reactions have widely been used, but they cannot be related simply to the acidic property. Measurement of adsorption heat of such a small base as ammonia by calorimetry 33 is one powerful method to evaluate the number and strength of acid sites. By this method, the interaction between the acidic and basic materials is directly evaluated, and this gives an absolute measure of the amount and strength of acid.Temperature...

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“…For the characterization of zeolite and zeotype materials, among the different vibrational techniques, such as infrared (IR), Raman, inelastic neutron scattering (INS), and electron energy loss spectroscopy (EELS), to date, the most used is IR [8]. The acid strength and accessibility of OH groups can be measured using various probe molecules such as pyridine [9], carbon monoxide [10], and different nitriles [11] in low-pressure conditions and studied by transmission Fourier transform infrared spectroscopy (FTIR). Acetonitrile (CH 3 CN) appears to be an attractive probe for zeolite acidity study since it can be attached to strong and weak AS and show the difference between them [12].…”

Section: Introductionmentioning

confidence: 99%

Fine Tuning of Hierarchical Zeolite Beta Acid Sites Strength

Landripet,

Puškarić,

Robić

et al. 2023

Crystals

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Two different synthesis methods to obtain hierarchical Beta zeolite are investigated: direct synthesis using cetyltrimethylammonium bromide (CTAB) as a mesoporous template and post-synthesis desilication by etching with NaOH and TPAOH. The main focus of this study is to show the possibility of fine tuning of the acid site (OH) strength (Brønsted and Lewis acid sites) through wet impregnation of these hierarchical Beta zeolites with divalent metal cations (Mg2+, Co2+, Ni2+, Cu2+, and Zn2+), which are important for various applications. Fourier transform infrared spectroscopy (FTIR) and deuterated acetonitrile as the probe molecule were used as a powerful technique to analyze the quantity and number of Brønsted/Lewis acid sites in the modified zeolite Beta structure. Investigating the influence of different divalent metal cations with a comparable ionic radius on the acidity of the hierarchical Beta zeolites, the present research aims to shed light on the structure–activity relationship that determines their catalytic behavior, for the development of efficient and environmentally friendly catalysts for various industrial applications.

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FTi.r. spectroscopic study of gallium beta

Cited by 20 publications

References 13 publications

Brønsted Acidity of Isomorphously Substituted ZSM-5 by B, Al, Ga, and Fe. Density Functional Investigations

Brønsted Acidity of Isomorphously Substituted ZSM-5 by B, Al, Ga, and Fe. Density Functional Investigations

Acidic Property of MFI-Type Gallosilicate Determined by Temperature-Programmed Desorption of Ammonia

Fine Tuning of Hierarchical Zeolite Beta Acid Sites Strength

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