Selectivity and mechanism for skeletal isomerization of alkanes over typical solid acids and their Pt-promoted catalysts

Miyaji, Atsuyuki; Echizen, Tsuneo; Li, Lianshun; Suzuki, Tetsuo; Yoshinaga, Yusuke; Okuhara, Toshio

doi:10.1016/s0920-5861(02)00031-7

Cited by 38 publications

(30 citation statements)

References 31 publications

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“…[15] However, the intramolecular pathway of n-butane isomerization, which is typical for Pt-promoted solid acid catalysts, is usually turned into the intermolecular pathway with unpromoted acid catalysts. [13,34] Ex situ GC-MS analysis of the reaction products: To clarify the pathway (intra-or intermolecular) of the 13 C-label scrambling in n-butane, as well as the formation of isobutane and propane from n-butane, we have analyzed the products of the conversion of [1- 13 C]n-butane on H-ZSM-5 by using GC-MS. The GC-MS analysis was performed after extracting the products from the catalyst with Et 2 O.…”

Section: Resultsmentioning

confidence: 99%

Mechanism Studies of the Conversion of ¹³C‐Labeled n‐Butane on Zeolite H‐ZSM‐5 by Using ¹³C Magic Angle Spinning NMR Spectroscopy and GC–MS Analysis

Luzgin

Stepanov

Arzumanov

et al. 2005

Chemistry A European J

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By using 13C MAS NMR spectroscopy (MAS = magic angle spinning), the conversion of selectively 13C-labeled n-butane on zeolite H-ZSM-5 at 430-470 K has been demonstrated to proceed through two pathways: 1) scrambling of the selective 13C-label in the n-butane molecule, and 2) oligomerization-cracking and conjunct polymerization. The latter processes (2) produce isobutane and propane simultaneously with alkyl-substituted cyclopentenyl cations and condensed aromatic compounds. In situ 13C MAS NMR and complementary ex situ GC-MS data provided evidence for a monomolecular mechanism of the 13C-label scrambling, whereas both isobutane and propane are formed through intermolecular pathways. According to 13C MAS NMR kinetic measurements, both pathways proceed with nearly the same activation energies (E(a) = 75 kJ mol(-1) for the scrambling and 71 kJ mol(-1) for isobutane and propane formation). This can be rationalized by considering the intermolecular hydride transfer between a primarily initiated carbenium ion and n-butane as being the rate-determining stage of the n-butane conversion on zeolite H-ZSM-5.

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Section: Resultsmentioning

confidence: 99%

Mechanism Studies of the Conversion of ¹³C‐Labeled n‐Butane on Zeolite H‐ZSM‐5 by Using ¹³C Magic Angle Spinning NMR Spectroscopy and GC–MS Analysis

Luzgin

Stepanov

Arzumanov

et al. 2005

Chemistry A European J

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“…It is noteworthy that carbenium ion intermediates can easily undergo dimerization-cracking reaction to form byproducts or polymerize to give coke precursors [9,12]. In other words, rearrangement of carbenium ions can proceed via two possible mechanisms: bimolecular mechanism, which results in relatively low isoalkane selectivity, and monomolecular mechanism, where the selectivity in isopentane is high [3,9,12,25] C 0 + 10 iso C = 5 + iso C + 5 : Therefore, it is expected that hydrid transfer to carbocation followed by its desorption would relatively suppress the bimolecular pathway involving the reaction of C 5 cations (carbenium ions) with C 5 alkenes and rearrangement step would occur via monomolecular mechanism, leading to high selectivity. Figure 8 shows e ect of space velocity (WHSV) on npentane isomerization.…”

Section: E Ect Of H 2 /Nc 5 Molar Ratiomentioning

confidence: 99%

“…In recent years, owing to environmental regulations on gasoline composition, much attention has been paid to supply of clean gasoline with high RON, low content of ole ns and aromatics such as benzene, and low concentration of sulfur [1][2][3][4]. In this sense, isomerization of light para n using solid acid catalysts, as a key technology in the production of clean fuels, has been raised [2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%

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n-pentane isomerization over Pt-Al promoted sulfated zirconia nanocatalyst

et al. 2017

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Abstract. Platinum containing sulfated zirconia (Pt-SZ/Al) catalyst was prepared by precipitation method. Characterization of the prepared catalyst was performed using XRD and SEM, and catalytic activity was studied for isomerization of nC 5 at atmospheric conditions and temperatures of 180-240 C in a ow reactor. The e ects of reaction temperature, H 2 /nC 5 ratio, and WHSV were investigated. As revealed by SEM and XRD, the prepared sulfated zirconia was of nanoscale size and had predominantly tetragonal crystalline phase. n-pentane conversion increased with increasing temperature and selectivity decreased. The optimal reaction temperature was 220 C where n-pentane conversion and isopentane selectivity were 70% and 94%, respectively. The positive e ect of H 2 /nC 5 ratio was observed on nC 5 conversion and iC 5 selectivity in the investigated H 2 /nC 5 ratio range. This trend of variation was related to the role of acid and metallic sites on the reaction pathway. As expected, increase in the WHSV, which reduces contact time between reactant and catalyst, decreased nC 5 conversion and increased selectivity toward iC5. The RON of the product increased with increasing temperature; then, it showed slight decrease at higher temperature. The decrease in the activation energy was observed, which can be attributed to the di erent reaction mechanisms or di erent rate-determining steps.

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“…The latter catalysts are particularly advantageous as they are less corrosive and less prone to deactivation by the contaminants (i.e. water, sulfur) present in the feed [20,21]. Nevertheless, Pt-zeolites catalysts present some disadvantages such as high operating temperatures, high hydrogen pressure and lower acidity which, in the end, leads to lower selectivity to branched molecules [22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

Pinto

Szeto

Oueslati

et al. 2016

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-Heteropolyacids (HPA) immobilized onto SBA-15 silica were prepared by two different ways using either impregnation or encapsulation methodologies. Two Keggin-type HPA, H 3 PW 12 O 40 and H 4 SiW 12 O 40 were considered in this study. The resulting hybrid materials were fully characterized by N 2 adsorption-desorption isotherms, XRD, FT-IR, Raman, diffuse reflectance UV-Vis spectroscopies and 31 P MAS NMR. All characterization methods showed that at room temperature the catalysts contained well-dispersed and intact Keggin units throughout the solid. The catalytic activity of these solids was investigated in the isomerization of n-hexane. The impregnated and encapsulated phosphotungstic catalysts performed similarly in catalysis showing that the amount of active sites was nearly the same in both catalysts. On the contrary, the tungstosilicic encapsulated material was completely inactive while its impregnated counterpart was even more active than the phosphotungstic derived catalysts. The acidity of the solids was measured by various methods: microcalorimetry of ammonia adsorption, ammonia desorption followed by Temperature Programmed Desorption (TPD) and DRIFT/GC-MS and pyridine adsorption followed by infrared spectroscopy. Only pyridine adsorption and ammonia desorption followed by DRIFT/GC-MS agreed with the catalytic data. Ammonia adsorption followed by microcalorimetry was not able to differentiate between the four catalysts while the TPD experiments led to unreliable results, as not only the evolved ammonia but also other molecules such as water were taken into account in the measurements. The behavior difference between the encapsulated silico-and phosphotungstic acids was explained by a more pronounced encapsulation in the case of silicon. de préparation. L'activité catalytique de ces matériaux a ensuite été étudiée dans l'isomérisation du n-hexane.

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Selectivity and mechanism for skeletal isomerization of alkanes over typical solid acids and their Pt-promoted catalysts

Cited by 38 publications

References 31 publications

Mechanism Studies of the Conversion of ¹³C‐Labeled n‐Butane on Zeolite H‐ZSM‐5 by Using ¹³C Magic Angle Spinning NMR Spectroscopy and GC–MS Analysis

Mechanism Studies of the Conversion of ¹³C‐Labeled n‐Butane on Zeolite H‐ZSM‐5 by Using ¹³C Magic Angle Spinning NMR Spectroscopy and GC–MS Analysis

n-pentane isomerization over Pt-Al promoted sulfated zirconia nanocatalyst

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

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Selectivity and mechanism for skeletal isomerization of alkanes over typical solid acids and their Pt-promoted catalysts

Cited by 38 publications

References 31 publications

Mechanism Studies of the Conversion of 13C‐Labeled n‐Butane on Zeolite H‐ZSM‐5 by Using 13C Magic Angle Spinning NMR Spectroscopy and GC–MS Analysis

Mechanism Studies of the Conversion of 13C‐Labeled n‐Butane on Zeolite H‐ZSM‐5 by Using 13C Magic Angle Spinning NMR Spectroscopy and GC–MS Analysis

n-pentane isomerization over Pt-Al promoted sulfated zirconia nanocatalyst

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

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Mechanism Studies of the Conversion of ¹³C‐Labeled n‐Butane on Zeolite H‐ZSM‐5 by Using ¹³C Magic Angle Spinning NMR Spectroscopy and GC–MS Analysis

Mechanism Studies of the Conversion of ¹³C‐Labeled n‐Butane on Zeolite H‐ZSM‐5 by Using ¹³C Magic Angle Spinning NMR Spectroscopy and GC–MS Analysis