Quantitative FTIR studies of hexagonal and cubic faujasites by pyridine and CO adsorption Numbers and relative acidity of the HF and LF zeolitic hydroxy groups

Cairon, Olivier; Chevreau, Thérèse

doi:10.1039/a703444j

Cited by 42 publications

(67 citation statements)

References 7 publications

(10 reference statements)

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“…The extent of the IR band shift depends on the acid strength, which was not only experimentally summarized by Paukshtis and Yurchenko, but also its relationship with the deprotonation energy was analyzed by quantum chemical calculations . However, it was claimed that the interaction of CO with the LF(OH) (low‐frequency band) of HY zeolite was hindered by not only steric but also solvation effects; therefore, the characterization was made only on a large pore HF(OH) located in a twelve‐membered ring of Y zeolite without problems . In addition, the shift degree depended on the composition of Si/Al in the framework of Y zeolite.…”

Section: Comparison Of the Sequences Of Acid Strengths Measured By Vamentioning

confidence: 99%

New Method for the Temperature- Programmed Desorption (TPD) of Ammonia Experiment for Characterization of Zeolite Acidity: A Review

Niwa

Katada

2013

The Chemical Record

172

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In this review, a method for the temperature-programmed desorption (TPD) of ammonia experiment for the characterization of zeolite acidity and its improvement by simultaneous IR measurement and DFT calculation are described. First, various methods of ammonia TPD are explained, since the measurements have been conducted under the concepts of kinetics, equilibrium, or diffusion control. It is however emphasized that the ubiquitous TPD experiment is governed by the equilibrium between ammonia molecules in the gas phase and on the surface. Therefore, a method to measure quantitatively the strength of the acid site (∆H upon ammonia desorption) under equilibrium-controlled conditions is elucidated. Then, a quantitative relationship between ∆H and H0 function is proposed, based on which the acid strength ∆H can be converted into the H0 function. The identification of the desorption peaks and the quantitative measurement of the number of acid sites are then explained. In order to overcome a serious disadvantage of the method (i.e., no information is provided about the structure of acid sites), the simultaneous measurement of IR spectroscopy with ammonia TPD, named IRMS-TPD (infrared spectroscopy/mass spectrometry-temperature-programmed desorption), is proposed. Based on this improved measurement, Brønsted and Lewis acid sites were differentiated and the distribution of Brønsted OH was revealed. The acidity characterized by IRMS-TPD was further supported by the theoretical DFT calculation. Thus, the advanced study of zeolite acidity at the molecular level was made possible. Advantages and disadvantages of the ammonia TPD experiment are discussed, and understanding of the catalytic cracking activity based on the derived acidic profile is explained.

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Section: Comparison Of the Sequences Of Acid Strengths Measured By Vamentioning

confidence: 99%

New Method for the Temperature- Programmed Desorption (TPD) of Ammonia Experiment for Characterization of Zeolite Acidity: A Review

Niwa

Katada

2013

The Chemical Record

172

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“…Nevertheless, the signal around 1455 cm -1 did not show important changes, although its intensity diminished slightly, with the increase of the desorption temperature. However, spectra of HT760 (Figure 11c) showed the disappearance of the signal around with the diminution of the acid-density [57][58][59] . Instead, the band at 1545 cm -1 disappears, in the solids NHT and HT560, at higher desorption temperatures than the solid HT760 (Figure 11), suggesting that Brönsted acid-sites with superior strength occur in samples with the highest densities of acid-sites.…”

Section: Brönsted and Lewis Aciditymentioning

confidence: 99%

FTIR study of the relation, between extra-framework aluminum species and the adsorbed molecular water, and its effect on the acidity in ZSM-5 steamed zeolite

Isernia

2013

Mat. Res.

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The infrared spectroscopy study of zeolite samples, obtained by steam treatment at 560-960 °C of the ZSM-5 catalyst (framework Si/Al ratio of 13), suggests an association between adsorbed molecular water and extra-framework aluminum hydroxyls generated after treatment. Moreover, infrared spectroscopy of adsorbed pyridine shows the reduction of the densities of Brönsted and Lewis sites, when treatment temperature rises, with contradicts the frequently accepted mechanism of the transformation of two bridged Si-OH-Al groups for each Lewis site generated. The gradual conversion of the octahedral extra-framework aluminum (Lewis-associated) in polymeric species with low acidity is the most probable cause of this behavior. On the other hand, the apparent decline of the acid Brönsted strength, with the increase in the temperature of the hydrothermal treatment, has two possible causes: a) the decreasing accessibility, of the pyridine molecular probe to bridged Si-OH-Al groups with the strongest Brönsted acidity, inside the channels, and b) the gradual transformation of these groups into extra framework species of weak acidity.

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“…The figure 1 shows the OH range of the spectra after pretreatment at 723K followed As they grow simultaneously with CO loading, they can be assigned to the (OH) and This position is indicative of strong Brønsted sites (with strength similar, for example, to that of Brønsted sites in HY zeolites [2,17]). This conclusion is confirmed by the analysis of the (OH) range where three bands are detected at low CO loading: two negative (OH) bands at 3688 and 3609 cm -1 and a broad band centred at ca 3440 cm -1 which appears to be the juxtaposition of two bands at ca.…”

Section: I5 Resultsmentioning

confidence: 99%

On the influence of water traces on the acidity measurement of amorphous aluminosilicates

et al. 2014

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For the measurement of their acidity, amorphous aluminosilicates are beforehand treated at temperature of 450°C or higher in order to remove water adsorbed on their surface. We will show in this study that, during the standard course of an acidity measurement by low temperature CO adsorption, traces of water present in the setup may perturb the acidity measurement by desorbing from the setup and adsorbing on the sample. We will also demonstrate that the interaction of water occurs on mild and strong Lewis sites and leads to the detection of stronger Brønsted sites than those natively present in the amorphous aluminosilicate. We will finally propose an experimental procedure that allows avoiding the adsorption on water on the sample and will clearly identify the position of the band associated with H 2 O and D 2 O adsorbed on Lewis sites before and after addition of CO. I.2. Highlights Unwanted H 2 O adsorption modifies acidity distribution in standard conditions A procedure is proposed to suppress water readsorption during acidity measurement

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Quantitative FTIR studies of hexagonal and cubic faujasites by pyridine and CO adsorption Numbers and relative acidity of the HF and LF zeolitic hydroxy groups

Cited by 42 publications

References 7 publications

New Method for the Temperature- Programmed Desorption (TPD) of Ammonia Experiment for Characterization of Zeolite Acidity: A Review

New Method for the Temperature- Programmed Desorption (TPD) of Ammonia Experiment for Characterization of Zeolite Acidity: A Review

FTIR study of the relation, between extra-framework aluminum species and the adsorbed molecular water, and its effect on the acidity in ZSM-5 steamed zeolite

On the influence of water traces on the acidity measurement of amorphous aluminosilicates

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