Influence of the Nature of Residual Alkali Cations on the Catalytic Activity of Zeolites X, Y, and EMT in their Brønsted Acid Forms

Weihe, M.; Hunger, Michael; Breuninger, Marcus; Karge, Hellmut G.; Weitkamp, Jens

doi:10.1006/jcat.2000.3137

Cited by 52 publications

(43 citation statements)

References 17 publications

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“…Rare-earth ions are often introduced into the zeolites for enhancing the hydrothermal stability as well as for generating acidic sites through hydrolysis of cation hydrates. 3,4 Since the position of the rare earth ions greatly influences the hydrothermal stability, adsorptive properties and catalytic activity of the zeolite, it becomes one of the critical problems to be tackled.…”

Section: Introductionmentioning

confidence: 99%

On configuration of exchanged La3+ on ZSM-5: A theoretical approach to the improvement in hydrothermal stability of La-modified ZSM-5 zeolite

Yang

Wang

Zhou

et al. 2003

The Journal of Chemical Physics

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Density functional calculations have been employed to investigate the locating and binding of lanthanum cation, i.e., La͑OH) 2 ϩ , on HZSM-5 zeolite. Through geometry optimization, it was determined that lanthanum ions are favorably accommodated in the two 6-T rings of the straight channels ͑Clusters 1 and 2, see Sec. III A for details͒. Cluster 1 was found to exist in prior to Cluster 2 due to the preference of Al substitution in the T11 site ͑Cluster 1͒ rather than in the T8 site ͑Cluster 2͒. Geometry-optimization of Cluster 1 containing another two lanthanide ions Nd 3ϩ and Yb 3ϩ was also carried out and it was found that a monotonic decrease in Ln-O bond length will take place as the atomic number increases, conforming well to the rule of lanthanide contraction. Some of the optimized parameters are comparable to the corresponding experimental values in Y zeolite, which confirms that the optimized configurations are acceptable. The average frequencies of hydroxyls attached to La 3ϩ or Yb 3ϩ in Cluster 1 fall at 3609.16 and 3579.76 cm Ϫ1 , respectively, with the gap of these two frequencies close to that in the sodalite cage of Y zeolite. Compared to H-form zeolite, the charges on both Al and O atoms in Ln-ZSM-5 zeolite show an obvious increase, which will undoubtedly lead to a stronger mutual interaction and hence enhance the stability of the ͓AlO 4 ͔ Ϫ anion. Moreover, the Ln͑OH) 2 ϩ seem to have thickened the zeolite framework, which can effectively retard the process of dealumination. Through the evaluation of the possibility for dimer formation, it turned out that when the exchange degree arrived to approximately 0.28, lanthanum monomers began to aggregate into dimers, and were completely converted into dimers when the exchange degree approached 0.60.

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Section: Introductionmentioning

confidence: 99%

On configuration of exchanged La3+ on ZSM-5: A theoretical approach to the improvement in hydrothermal stability of La-modified ZSM-5 zeolite

Yang

Wang

Zhou

et al. 2003

The Journal of Chemical Physics

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“…or Si(4 -n)Si, indicating that each Si atom is linked through oxygen to n aluminium and 4 -n silicon neighbors [37]. Applying 29Si NMR spectroscopy it was found that the exchange of zeolite Na-Y with lanthanum, cerium, samarium, potassium, calcium, barium and magnesium cations and subsequent dehydration brings about high field shift of Si(nAl) signals, where n is the number of aluminium atoms in the second coordination sphere of the resonating silicon atom [15,38]. Consistent with the observed results K-Y, Mg-Y and K+ and Mg2+ exchanged rare earth zeolites exhibited a high field shift over Na" exchanged samples (Fig.…”

Section: Nmr Studiesmentioning

confidence: 99%

Influence of residual cations (Na+, K+ and Mg2+) in the alkylation activity of benzene with 1-octene over rare earth metal ion exchanged FAU–Y zeolite

Thomas

Sugunan

2004

Microporous and Mesoporous Materials

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Influence of residual cations (Na", K+ and Mg2+) AbstractThe effect of residual cations in rare earth metal modified faujasite-Y zeolite has been monitored using magic angle spinning NMR spectral analysis and catalytic activity studies. The second metal ions being used are Na", K+ and Mg". From a comparison of the spectra of different samples, it is concluded that potassium and magnesium exchange causes a greater downfield shift in the 29Si NMR peaks. Also, lanthanum exchanged samples show migration behavior from large cages to small cages, which causes the redistribution of second counter cations. It is also observed that Mg2+ causes the most effective migration of lanthanum ions due to its greater charge. The prepared systems were effectively employed for the alkylation of benzene with l-octene in the vapor phase. From the deactivation studies it is observed that the as-exchanged zeolites possess better stability towards reaction condition over the pure HFAU zeolite.

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“…Another important issue is the need to upgrade heavy cuts and other low-cost feedstocks to increase the throughput of gasoline and diesel pools, thus improving the profitability of the refinery. In the case of gasoline, one attractive option is to process waxy feedstocks [1][2][3][4] , which demands the use of the hydroisomerization-cracking process to form branched paraffins with high octane numbers. Alkanes with more than seven carbon atoms are easily cracked; thus, the requirements for long paraffin isomerization-cracking catalysts are as follows: (i) high selectivity for branched isomers; (ii) low selectivity for light gases; and (iii) low environmental impact.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, inconveniently long isomers of low volatility and low octane number are obtained. 5 Some isomerization catalysts currently in use are corrosive and contaminating (sulfuric acid, fluorhydric acid, alumina-supported AlCl 3 , etc), and their disposal poses many problems to refiners. High liquid yields and high selectivity for branched isoparaffins can be notably obtained by using oxoanion-promoted zirconia catalysts.…”

Section: Introductionmentioning

confidence: 99%

Isomerization-cracking of n-octane on catalysts based on heteropolyacid H3Pw12O40 and heteropolyacid supported on zirconia and promoted with Pt and Cs

Manuale¹,

Torres²,

Benítez³

et al. 2013

Quím. Nova

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Recebido em 10/9/12; aceito em 1/3/13; publicado na web em 4/6/13Isomerization-cracking of n-octane was studied using H 3 PW 12 O 40 (HPA) and HPA supported on zirconia and promoted with Pt and Cs. The addition of Pt and Cs to the supported HPA did not modify the Keggin structure. The Pt addition to the supported HPA did not substantially modify the total acidity; however, the Brönsted acidity increased significantly. Cs increased the total acidity and Brönsted acidity. A linear relation was observed between the n-C 8 total conversion and Brönsted acidity. The most adequate catalysts for performing isomerization and cracking to yield high research octane number (RON) are those with higher values of Brönsted acidity.

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Influence of the Nature of Residual Alkali Cations on the Catalytic Activity of Zeolites X, Y, and EMT in their Brønsted Acid Forms

Cited by 52 publications

References 17 publications

On configuration of exchanged La3+ on ZSM-5: A theoretical approach to the improvement in hydrothermal stability of La-modified ZSM-5 zeolite

On configuration of exchanged La3+ on ZSM-5: A theoretical approach to the improvement in hydrothermal stability of La-modified ZSM-5 zeolite

Influence of residual cations (Na+, K+ and Mg2+) in the alkylation activity of benzene with 1-octene over rare earth metal ion exchanged FAU–Y zeolite

Isomerization-cracking of n-octane on catalysts based on heteropolyacid H3Pw12O40 and heteropolyacid supported on zirconia and promoted with Pt and Cs

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