The Effect of Type of Acid Sites in Molecular Sieves on Activity and Selectivity in Acylation Reactions

2007 ◽  
Vol 72 (5-6) ◽  
pp. 728-746 ◽  
Author(s):  
Martina Bejblová ◽  
Josef Vlk ◽  
Dana Procházková ◽  
Helena Šiklová ◽  
Jiří Čejka
Keyword(s):  
Molecular Sieves ◽  
Molecular Sieve ◽  
Acid Sites ◽  
Acid Strength ◽  
Zeolite Beta ◽  
Mesoporous Molecular Sieves ◽  
Lewis Acid Sites ◽  
Mcm 41 ◽  
Acylation Reactions

The role of the type of acid site (Broensted vs. Lewis) on the activity and selectivity of molecular sieve catalysts was investigated in ferrocene and toluene acylation. H-, Zn-, Fe-, Al- and La-forms of zeolite Beta, USY and mesoporous molecular sieves (Al)MCM-41, (Al)SBA-15 were tested. It was observed that addition of metal cations acting as Lewis acid sites can increase the acidity of various molecular sieve catalysts. No general relationship between the type of cation and conversion of individual substrate was found. While the highest activity in ferrocene acylation was observed after addition of Zn, in the case of toluene acylation Al-forms of catalysts were the most active. The results indicate that the acid strength of cationic Lewis sites controls their activity in acylation reactions.

Synthesis and Catalytic Application of Mesoporous Molecular Sieves MCM-41 Containing Niobium and Tantalum

2007 ◽  
Vol 124-126 ◽  
pp. 1761-1764 ◽  
Author(s):  
Hun Jung ◽  
Kwang Deog Jung ◽  
Oh Shim Joo ◽  
Sun Jin Kim
Keyword(s):  
Vapor Phase ◽  
Molecular Sieves ◽  
Catalytic Performance ◽  
Acid Sites ◽  
Weak Acid ◽  
Beckmann Rearrangement ◽  
Mesoporous Molecular Sieves ◽  
Cyclohexanone Oxime ◽  
Catalytic Application ◽  
Mcm 41

Niobium- and tantalum-containing mesoporous molecular sieves MCM-41 have been synthesized, and applied as a catalyst for vapor phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam. NbMCM-41 catalyst exhibited high catalytic performance in the vapor phase Beckmann rearrangement of cyclohexanone oxime. The oxime conversions were almost 100% and the lactam selectivities were around 80%. The lactam selectivities of NbMCM-41 catalyst were higher than those of AlMCM-41 catalyst. However, TaMCM-41 catalyst exhibited lower catalytic performance than AlMCM-41 catalyst, and it was fast deactivated with time. These results may be due to the acidity difference among the catalysts. The results from NH3-TPD showed that NbMCM-41 catalyst possessed weak and medium acid sites, while TaMCM-41 catalyst possessed only very weak acid sites. AlMCM-41 catalyst also exhibited only weak acid sites.

Synthesis and Catalytic Property of V-MCM-41 Mesoporous Molecular Sieves by Atrane Route

2011 ◽  
Vol 284-286 ◽  
pp. 936-939 ◽  
Author(s):  
Wen Ming Liu ◽  
Jia Jia Cao ◽  
Chun Ling Fan ◽  
Zhao Ping Chen
Keyword(s):  
Gas Phase ◽  
Atmospheric Pressure ◽  
Molecular Sieves ◽  
Molecular Sieve ◽  
Space Velocity ◽  
Vanadium Content ◽  
Mesoporous Molecular Sieves ◽  
Active Centers ◽  
Partial Oxidation Of Toluene ◽  
Mcm 41

V-MCM-41 molecular sieve with high vanadium content has been prepared by the atrane route. Gas phase partial oxidation of toluene to benzaldehyde on the V-MCM-41 molecular sieves catalysts was studied. The structure and characteristic of catalyst were characterized by means of XRD, UV-vis and so on. The experimental results showed that the vanadium content in the framework related to mole ratio of silica to vanadium. The vanadium content in the framework was the highest, when the mole ratio of Si to V was 30. And the vanadium in the framework may be active centers of catalytic oxidation of toluene to benzaldehyde. Under the condition of atmospheric pressure, mole ratio of Si to V 30, space velocity 800 h-1, n(air):n(toluene)=5 and reaction temperature 450°C，the conversion of toluene, selectivity to benzaldehyde and its yield were 20.8%, 41.8% and 8.7% respectively.

Effect of rehydration on the porosity of MCM-41 mesoporous molecular sieves

1999 ◽  
Vol 35 (1) ◽  
pp. 52-56
Author(s):  
F. M. Bobonich ◽  
Yu. G. Voloshina ◽  
L. A. Matkovskaya ◽  
V. N. Solomakha ◽  
Yu. G. Gol’tsov
Keyword(s):  
Molecular Sieves ◽  
Mesoporous Molecular Sieves ◽  
Mcm 41

scholarly journals Hoveyda–Grubbs type metathesis catalyst immobilized on mesoporous molecular sieves MCM-41 and SBA-15

2011 ◽  
Vol 7 ◽  
pp. 22-28 ◽  
Author(s):  
Hynek Balcar ◽  
Tushar Shinde ◽  
Naděžda Žilková ◽  
Zdeněk Bastl
Keyword(s):  
Nmr Spectroscopy ◽  
Molecular Sieves ◽  
Direct Interaction ◽  
Mesoporous Molecular Sieves ◽  
Support Surface ◽  
Wall Surface ◽  
Ring Closing Metathesis ◽  
Immobilized Catalysts ◽  
Metathesis Catalyst ◽  
Mcm 41

A commercially available Hoveyda–Grubbs type catalyst (RC303 Zhannan Pharma) was immobilized on mesoporous molecular sieves MCM-41 and on SBA-15 by direct interaction with the sieve wall surface. The immobilized catalysts exhibited high activity and nearly 100% selectivity in several types of alkene metathesis reactions. Ru leaching was found to depend on the substrate and solvent used (the lowest leaching was found for ring-closing metathesis of 1,7-octadiene in cyclohexane – 0.04% of catalyst Ru content). Results of XPS, UV–vis and NMR spectroscopy showed that at least 76% of the Ru content was bound to the support surface non-covalently and could be removed from the catalyst by washing with THF.

Role of Zinc in Zn-Loaded ZSM-5 Zeolites in the Aromatization of n-Hexane

1999 ◽  
Vol 64 (1) ◽  
pp. 168-176 ◽  
Author(s):  
Edita Rojasová ◽  
Agáta Smiešková ◽  
Pavol Hudec ◽  
Zdenek Židek
Keyword(s):  
Solid State ◽  
Ion Exchange ◽  
Lewis Acid ◽  
Acid Site ◽  
Acid Sites ◽  
Partial Migration ◽  
Simultaneous Presence ◽  
Lewis Acid Sites ◽  
Strong Lewis Acid

Aromatization of n-hexane over zinc-modified ZSM-5 zeolites was investigated. It was shown that incorporation of zinc by ion exchange into cationic positions of NH4-ZSM-5 zeolite causes acid-site strength redistribution and generation of new relatively strong Lewis acid sites in zeolite increasing the selectivity of n-hexane aromatization in comparison with the parent NH4-ZSM-5 zeolite. Simultaneous presence of Lewis and Broensted acid sites in ZSM-5 zeolite does not affect the strength of Broensted acid sites in zeolite. For the activity/selectivity of aromatization of n-hexane on Zn-modified ZSM-5 zeolites, the amount of Zn and its localization in the cationic positions are decisive. The reaction of n-hexane can be also initiated by the Zn species alone in the cationic positions. ZnO species alone as an extraframework phase was found inactive in the catalyst for aromatization of n-hexane. The influence of ZnO addition on the performance of pure ammonium forms of ZSM-5 zeolites in n-hexane conversion is a result of partial migration of zinc into cationic positions of zeolite by solid-state ion exchange.

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