On the nature of framework Brønsted and Lewis acid sites in ZSM-5

Woolery, G. L.; Kuehl, G. H.; Timken, Hye-Kyung; Chester, Arthur W.; Vartuli, J.C.

doi:10.1016/s0144-2449(97)00086-9

Cited by 281 publications

(232 citation statements)

References 14 publications

Supporting

Mentioning

210

Contrasting

Unclassified

Order By: Relevance

“…It can be seen that there are two peaks with centers at $275 C and $475 C. The low temperature peak corresponds to the weakly bound ammonia on non-framework Lewis acid sites whereas the high temperature peak corresponds to the more strongly bound ammonia on Brønsted acid sites. 36 As reported in Table 8 the total acidity of the catalyst decreases after the 10 reaction-regeneration cycles. From the TPD curve it appears that the loss in acidity is due to C. Fresh is the catalyst as-received after calcining and spent is the catalyst after 10 reaction-regeneration cycles.…”

Section: 35mentioning

confidence: 91%

“…The TPD data show the total acidity of the composite catalyst decreases with repeated reaction/regeneration cycles, however, this loss in acidity appears to be from a loss of the weak nonframework Lewis acid sites in the non-zeolite components of the catalyst (such as alumina). 36 The actual zeolite acid sites are not likely lost as the high temperature TPD peak and the ratio of Brønsted to Lewis acid sites in the zeolite measured by DRIFTS remain constant. From the ICP-OES the metals, calcium, potassium, magnesium and manganese, are deposited on the catalyst after the repeated reaction-regeneration cycles.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Production of green aromatics and olefins by catalytic fast pyrolysis of wood sawdust

Carlson

Cheng

Jae

et al. 2011

Energy Environ. Sci.

532

425

View full text Add to dashboard Cite

Section: 35mentioning

confidence: 91%

mentioning

confidence: 99%

Production of green aromatics and olefins by catalytic fast pyrolysis of wood sawdust

Carlson

Cheng

Jae

et al. 2011

Energy Environ. Sci.

532

425

View full text Add to dashboard Cite

“…34 Another resonance signal in the 27 Al MAS NMR spectra is found at 0 ppm, which is known to originate from octahedral framework Al (OFAl). 35,36 Three other vibrational bands, located at 3721 cm À1 , 3742 cm À1 , and 3780 cm À1 , can be found in the FT-IR spectra. These bands correspond to internal silanol groups, external silanol groups and external Al-OH groups, respectively.…”

Section: Effect Of Thermal and Acid Treatmentmentioning

confidence: 95%

Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

Bij

Weckhuysen

2014

Phys. Chem. Chem. Phys.

127

View full text Add to dashboard Cite

In order to elucidate phosphorus-zeolite H-ZSM-5 interactions, a variety of phosphorus-modified zeolite H-ZSM-5 materials were studied in a multi-spectroscopic manner. By deploying single pulse 27 Al, 31 P MAS NMR, 2D heteronuclear 27 Al-31 P correlation (HETCOR), 27 Al MQ MAS NMR spectroscopy, TPD of pyridine monitored by FT-IR spectroscopy, and Scanning Transmission X-ray Microscopy (STXM) the interplay and influence of acidity, thermal treatment and phosphorus on the structure and acidity of H-ZSM-5 were established. It was found that while acid treatment did not affect the zeolite structure, thermal treatment leads to the breaking of Si-OH-Al bonds, a decrease in the strong acid site number and the formation of terminal Al-OH groups. No extra-framework aluminium species was observed. Phosphorus precursors interact with the zeolitic framework through hydrogen bonds and physical coordination, as phosphorus species can be simply washed out with hot water. After phosphatation and thermal treatment two effects occur simultaneously, namely (i) phosphorus species transform into water insoluble condensed poly-phosphoric acid and (ii) phosphoric acid binds irreversibly to the terminal Al-OH groups of partially dislodged four-coordinated framework aluminium, forming local silico-aluminophosphate interfaces.These interfaces are potentially the promoters of hydrothermal stability in phosphated zeolite H-ZSM-5.

show abstract

“…Two responses, corresponding to the weak (Lewis) and the strong (Brønsted) acids, could be specified in 170-270 • C and 270-500 • C [28,29]. Compared to the temperature of the maximum desorption rate (T max ) of the Lewis acid of HZ (228 • C), HZ-D and HZ-DA had higher T max 's (252 and 250 • C, respectively), this increase in the temperature of desorption was possibly caused by newly-created Lewis acidic Al debris, such as Al(OH 2 ) + or Al(OH) 2+ [30,31]. The concentration of the Lewis acid increased from 0.08 mmol/g (HZ) to 0.10 mmol/g (HZ-D), underlining newly-formed Lewis acidic Al on HZ-D. After acid treatment, the Lewis acid concentration decreased to 0.05 mmol/g (HZ-DA), indicating that non-framework Al species can be mostly removed by the acid treatment.…”

Section: Resultsmentioning

confidence: 99%

The Role of Non-Framework Lewis Acidic Al Species of Alkali-Treated HZSM-5 in Methanol Aromatization

et al. 2017

View full text Add to dashboard Cite

Mesoporous HZSM-5 prepared by alkaline treatment (also termed desilication) has drawn significant attention due to its potential in large-scale production and in versatile applications, such as separation and catalysis. Alkali-treated HZSM-5 contains considerable amounts of non-framework (amorphous) Lewis acidic Al species on the external surface, and is deemed to be essential in affecting its catalytic performances. This study intends to clarify the catalytic nature of amorphous Al species of alkali-treated HZSM-5 in methanol aromatization. Physicochemical characterizations, including N 2 adsorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), magic-angle-spinning nuclear magnetic resonance (MAS NMR), inductively coupled plasma (ICP) analysis, NH 3 temperature-programmed desorption (TPD), and methanol-TPD, were performed. The outcomes showed that non-framework Al promotes the hydride transfer in mesoporous HZSM-5, thereby facilitating the aromatization reaction. Among aromatic products, durene can be promoted by non-framework Al through methylation/transalkylation of other aromatics, particularly xylenes, instead of being promoted by reduced space confinement in mesoporous HZSM-5.

show abstract

On the nature of framework Brønsted and Lewis acid sites in ZSM-5

Cited by 281 publications

References 14 publications

Production of green aromatics and olefins by catalytic fast pyrolysis of wood sawdust

Production of green aromatics and olefins by catalytic fast pyrolysis of wood sawdust

Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

The Role of Non-Framework Lewis Acidic Al Species of Alkali-Treated HZSM-5 in Methanol Aromatization

Contact Info

Product

Resources

About