Characterization of the acid sites in dealuminated nanosized HZSM-5 zeolite with the probe molecule trimethylphosphine

Zhang, Weiping; Han, Xiuwen; Liu, Xiumei; Bao, Xinhe

doi:10.1016/s1381-1169(02)00466-1

Cited by 39 publications

(17 citation statements)

References 37 publications

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“…A possible explanation for this behavior is the increasing condensation of the extra-framework aluminum hydroxyls to polymeric aluminum species. Such behavior was already been discussed in the literature 1,12 . Nevertheless, the difference of the spectra of the solids NHT, HT560 and HT760 minus HT960 (Figure 4) provides evidence of a small signal centered at 1622 cm -1 that agrees well with the deformation vibration of physically adsorbed molecular water [37][38][39][40] ; whose intensity decreases with the increasing temperature of the hydrothermal treatment.…”

Section: Temperature-programmed Desorption Of Ammonia (Tpd-nh 3 )supporting

confidence: 60%

“…This contradicts the frequently accepted mechanism that underlies the increasing number of Lewis acid sites at the expense of the bridged Si-OH-Al sites [1][2][3][4][5] , associated with Brönsted acidity, after hydrothermal treatment. This behavior may be attributed to the decreasing accessibility of pyridine molecules to Lewis acid sites inside the zeolite channels.…”

Section: Brönsted and Lewis Aciditymentioning

confidence: 80%

“…Several authors have propused [1][2][3][4][5] that the interaction between two bridged Si-OH-Al sites, associated 6 with Brönsted acidity, generate an extra-framework Al(OH) 2+ (or AlO + ), which has been considered [7][8][9] as the true carrier of Lewis acidity. It is generally accepted that the extra-framework aluminum (EFAL) generated after hydrothermal treatment is deposited in the form of 4, 5 and 6 coordinate monomeric species 10,11 , where 5 and 6 are related with the Lewis acidity in zeolites.…”

Section: Introductionmentioning

confidence: 99%

“…It is generally accepted that the extra-framework aluminum (EFAL) generated after hydrothermal treatment is deposited in the form of 4, 5 and 6 coordinate monomeric species 10,11 , where 5 and 6 are related with the Lewis acidity in zeolites. On the other hand, the formation of four-coordinate polymeric aluminum species of low acidity on the surface zeolite crystals, has been reported 1,12 . Zeolite MFI is an interesting shape-selective solid acid catalyst.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Temperature-programmed Desorption Of Ammonia (Tpd-nh 3 )supporting

confidence: 60%

Section: Brönsted and Lewis Aciditymentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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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“…2, it can be seen that at a higher WHSV of 4.2 h -1 , the light olefin selectivity decreased slowly with time on stream. Due to the presence of some free Brønsted acid sites, 2Ca/2 # -HZSM-5 was subjected to steam treatment [16][17][18][19]. The obtained sample showed that the run time for complete methanol conversion increased from 13 to 75 h and the maximum propylene selectivity reached up to 48.7%.…”

Section: Resultsmentioning

confidence: 99%

Ca modified ZSM-5 for high propylene selectivity from methanol

Zhang

Gao

et al. 2010

Reac Kinet Mech Cat

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The highest propylene selectivity and best catalytic stability were gained over Ca modified ZSM-5 that had little free Brønsted acid sites, which indicated that Ca interacted with Brønsted acid sites and thus participated in the catalytic reaction as supported by the MTO data of Na modified ZSM-5. A possible mechanism that involves the formation of acid-base centers by hydrolyzing Ca species in the presence of water is suggested.

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NMR Spectroscopy for the Characterization of Surface Acidity and Basicity

Hunger

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Investigation of B rønsted Acidic Hydroxyl Groups by 1 H MAS NMR Spectroscopy Solid‐State NMR Characterization of the Accessibility and Strength of B rønsted Acid Sites by Probe Molecules Solid‐State NMR Investigations of L ewis Acid Sites by Probe Molecules Solid‐State NMR Investigations of Base Sites in Solid Catalysts

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Characterization of the acid sites in dealuminated nanosized HZSM-5 zeolite with the probe molecule trimethylphosphine

Cited by 39 publications

References 37 publications

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

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

Ca modified ZSM-5 for high propylene selectivity from methanol

NMR Spectroscopy for the Characterization of Surface Acidity and Basicity

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