Carbocation Formation in Zeolites. Uv-Vis-Nir Spectroscopic Investigations on Mordenites

Fejes, P.; Förster, H.; Kiricsi, Imre; Seebode, Jürgen

doi:10.1016/s0167-2991(09)61144-7

Cited by 7 publications

(5 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has already been stated that these wavelengths, characteristic of alkenyl carbenium ions formed in zeolites, agree well with those calculated by Sorensen's equation describing the frequency dependence of polyenylic carbenium ions as a function of the number of conjugated double bonds in the respective ion . Furthermore, the ability to form alkenyl ions of different hydrocarbons and their derivatives follows the same sequence as that observed in superacid solutions . The bands formed at ambient temperature are assigned to π−π* transitions of alkenyl carbenium ions, while those developing at higher temperatures might be attributed to substituted benzyl and/or polyalkylaromatic ions. , These investigations reveal very close similarities to events in superacidic solution.…”

Section: Assignment Of the Bands Generally Observed In The Uv−vis Spe...supporting

confidence: 83%

“…Sorensen's equation proves suitable for specification of the absorption maxima of mono-, di-, and trienylic carbenium ions. 145,245 Furthermore, the capability of adsorbates for alkenyl carbenium ion generation followed the same sequence found by Rosenbaum and Symons in superacids. 8 It has also been reported that both the overall as well as the Lewis acidity of the zeolites plays an important role in the course of alkenyl ion formation.…”

Section: Assignment Of the Bands Generally Observed In The Uv−vis Spe...supporting

confidence: 63%

“…The bands formed at ambient temperature are assigned to π−π* transitions of alkenyl carbenium ions, while those developing at higher temperatures might be attributed to substituted benzyl and/or polyalkylaromatic ions. , These investigations reveal very close similarities to events in superacidic solution. Sorensen's equation proves suitable for specification of the absorption maxima of mono-, di-, and trienylic carbenium ions. , Furthermore, the capability of adsorbates for alkenyl carbenium ion generation followed the same sequence found by Rosenbaum and Symons in superacids . It has also been reported that both the overall as well as the Lewis acidity of the zeolites plays an important role in the course of alkenyl ion formation. , Characteristic red shifts of the UV−vis bands were also observed in the case of zeolites and attributed to the formation of branched, i.e., alkyl-substituted, alkenyl carbenium ions.…”

Section: Assignment Of the Bands Generally Observed In The Uv−vis Spe...mentioning

confidence: 59%

“…139 Furthermore, the ability to form alkenyl ions of different hydrocarbons and their derivatives follows the same sequence as that observed in superacid solutions. 245 The bands formed at ambient temperature are assigned to π-π* transitions of alkenyl carbenium ions, while those developing at higher temperatures might be attributed to substituted benzyl and/or polyalkylaromatic ions. 103,246 These investigations reveal very close similarities to events in superacidic solution.…”

Section: Assignment Of the Bands Generally Observed In The Uv−vis Spe...mentioning

confidence: 98%

See 3 more Smart Citations

Generation, Characterization, and Transformations of Unsaturated Carbenium Ions in Zeolites

Kiricsi¹,

Förster²,

Tasi³

et al. 1999

Chem. Rev.

133

116

View full text Add to dashboard Cite

Section: Assignment Of the Bands Generally Observed In The Uv−vis Spe...supporting

confidence: 83%

Section: Assignment Of the Bands Generally Observed In The Uv−vis Spe...supporting

confidence: 63%

Section: Assignment Of the Bands Generally Observed In The Uv−vis Spe...mentioning

confidence: 59%

Section: Assignment Of the Bands Generally Observed In The Uv−vis Spe...mentioning

confidence: 98%

See 2 more Smart Citations

Generation, Characterization, and Transformations of Unsaturated Carbenium Ions in Zeolites

Kiricsi¹,

Förster²,

Tasi³

et al. 1999

Chem. Rev.

133

116

View full text Add to dashboard Cite

“…As in the separatebed case, the amount of CH 4 generated by the base catalyst alone is large compared to the mixed bed with 0.25 and 0.5 g ZSM-5. This is because ZSM-5 forms a C 1 carbenium ion (Fejes et al, 1984) and this ion further reacts with another molecule on ZSM-5 to form longer-chain hydrocarbons. Larger amounts of ZSM-5 increase the cracking of long-chain hydrocarbons (Martinez et al, 2005) and this increases the amount of methane formed.…”

Section: Gas Analysismentioning

confidence: 99%

Addition of Zeolite ZSM-5 to an Iron-based Fischer-Tropsch Catalyst supported on Activated Carbon: Effect of Reactor Conditions

Karre¹

View full text Add to dashboard Cite

An iron-based catalyst containing 6 wt% Mo, 16 wt% Fe, 0.8 wt% Cu, and 0.9 wt% K supported on Norit SX Ultra activated carbon is used as a FTS catalyst. Zeolite ZSM-5 (of medium acidity and Si/Al = 50) is used to check its effect on FT base catalyst to form aromatic compounds and to reduce the size of long-chain hydrocarbons. The influence of ZSM-5 amounts, bed arrangements, and the temperature on the product distribution were investigated. The performance of ZSM-5 along with the base catalyst was analyzed in two catalyst bed configurations: separate-bed and mixed-bed. Both separate-bed and mixed-bed catalyst arrangements show conversion of alcohols to hydrocarbons and water. The separate-bed arrangement gives higher conversions of CO and H 2 , and higher yields of liquid hydrocarbons. The decline in FT activity in the mixed bed is probably due to lowering of the alkali content of the iron catalyst because of alkali migration from FT catalyst to ZSM-5, as confirmed by energy-dispersive X-ray spectroscopy of the spent ZSM-5. Product profiles were analyzed for changing ZSM-5 weight from 50 to 200 % of the FTS amount in the separate bed and the mixed bed catalyst arrangements. Oligomerization, aromatization, isomerization, and cracking reactions are enhanced with increasing ZSM-5 weight in both the catalyst arrangements. The base catalyst shows no selectivity towards aromatic compounds, but addition of ZSM-5 in both arrangements forms C 7-10 aromatic compounds. Long-chain hydrocarbon molecules (C 13+) formed by the base catalyst are effectively cracked, and isomerized on the ZSM-5 catalyst surface in both type of catalyst arrangements. Product profiles were analyzed for change in the temperature from 280 to 320⁰C in the base catalyst as well as in the separate-bed catalyst arrangement. Amounts of small-chain hydrocarbons (C 1-5) increase with increase in temperature because of higher FTS rates. Liquid hydrocarbon production rate (in both the base catalyst and the separate bed) is increased at 300⁰C due to increase in FTS rate. Further increase in the temperature causes these rates to drop to give small-chain hydrocarbon (C 1-4) species. Aromatic yields are found to reach a maximum at 300⁰C in the separate bed. The alcohol rate for the base catalyst increases with increase in temperatures probably because of higher FTS rates. 280⁰C is sufficient to convert all the alcohols formed by the base catalyst in the separate bed. The base catalyst and ZSM-5 together were tested for 240 h time on stream (TOS) to check the stability of the combination of the catalysts in the separate-bed arrangement. The base catalyst shows stability up to 120 h and slow decline in activity up to 240 h. A progressive loss of the ZSM-5 activity occurred with TOS. Coke deposition on ZSM-5, confirmed by energy-dispersive X-ray spectroscopy, decreases aromatic compound yield, and increases olefin selectivity with time on stream due to reduction in oligomerization reactions.

show abstract

Generation of alkenyl-type carbocations from neopentane in HNaY zeolite

Förster

Kiricsi²,

Seebode

et al. 1988

React Kinet Catal Lett

View full text Add to dashboard Cite

Carbocation Formation in Zeolites. Uv-Vis-Nir Spectroscopic Investigations on Mordenites

Cited by 7 publications

References 13 publications

Generation, Characterization, and Transformations of Unsaturated Carbenium Ions in Zeolites

Generation, Characterization, and Transformations of Unsaturated Carbenium Ions in Zeolites

Addition of Zeolite ZSM-5 to an Iron-based Fischer-Tropsch Catalyst supported on Activated Carbon: Effect of Reactor Conditions

Generation of alkenyl-type carbocations from neopentane in HNaY zeolite

Contact Info

Product

Resources

About