Kinetics of Hydro-isomerization ofn-Hexane over Platinum Containing Zeolites

Runstraat, van de A; Kamp, JA; Stobbelaar, PJ Pieter; Grondelle, van J Joop; Krijnen, S Simon; Santen, van Ra Rutger

doi:10.1006/jcat.1997.1779

Cited by 93 publications

(68 citation statements)

References 28 publications

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“…Diffusion limitations will lower the apparent activation energy for n-C 7 hydroconversion when the prerequisites for a diffusional increase in apparent activation energy are not met (43)(44)(45), as is the case with TON-, MTT-, and AEL-type sieves. We find that the apparent activation energies for the FAU-, BEA-, TON-, and MTT-type zeolites are comparable (Table 3, estimated systematic error ±3 kJ/mol) and approach the true activation energy for hydroisomerization (43,46,47). This indicates that there are no diffusion limitations and therefore all of the zeolite acid sites are able to contribute to the n-C 7 hydroconversion (43,46,47), leaving little room for speculation that the n-C 7 hydroconversion in the TON-or MTT-type zeolites occurs predominantly at or near the pore mouth.…”

Section: Resultsmentioning

confidence: 89%

“…We find that the apparent activation energies for the FAU-, BEA-, TON-, and MTT-type zeolites are comparable (Table 3, estimated systematic error ±3 kJ/mol) and approach the true activation energy for hydroisomerization (43,46,47). This indicates that there are no diffusion limitations and therefore all of the zeolite acid sites are able to contribute to the n-C 7 hydroconversion (43,46,47), leaving little room for speculation that the n-C 7 hydroconversion in the TON-or MTT-type zeolites occurs predominantly at or near the pore mouth. The apparent activation energy of the AEL-type silicoaluminophosphate is lower than that of the zeolites (Table 3), indicating either a lower acid site coverage (due to its higher operation temperature (Table 3)) or the onset of diffusion limitations (43,45).…”

Section: Resultsmentioning

confidence: 89%

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The Shape Selectivity of Paraffin Hydroconversion on TON-, MTT-, and AEL-Type Sieves

Maesen

Schenk

Vlugt

et al. 1999

Journal of Catalysis

141

137

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Based on a comparison between simulated and measured adsorption properties, we demonstrate that both normal and monomethylparaffins are able to fully enter the pores of TON-, MTT-, and AEL-type molecular sieves. This disproves the theory that monomethylparaffins only partially enter these pores and that normal paraffins are predominantly hydroisomerized at the pore mouths of these sieves. Instead, we attribute the high selectivity for paraffins with terminal methyl groups to product shape selectivity, and the low selectivity for paraffins with neighboring methyl groups to transition state selectivity. These traditional shape selectivity concepts explain not only the detailed product distribution of n-heptane hydroconversion, but also that of longer-chain n-paraffins.

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Section: Resultsmentioning

confidence: 89%

Section: Resultsmentioning

confidence: 89%

The Shape Selectivity of Paraffin Hydroconversion on TON-, MTT-, and AEL-Type Sieves

Maesen

Schenk

Vlugt

et al. 1999

Journal of Catalysis

141

137

View full text Add to dashboard Cite

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“…Although alumina supported catalysts are more active at low temperatures, they are highly sensitive to poisoning by both water and sulfur and therefore require constant regeneration with chlorine which is hazardous and can potentially alter the structure of the precious metal. Consequently, enormous research effort has focused on using the more stable and environmental-friendly zeolite-based catalysts, since they possess the necessary acidity, internal structure and pore size distribution to be catalytically active and selective for these hydroisomerizations [6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Effect of the impregnation order on the nature of metal particles of bi-functional Pt/Pd-supported zeolite Beta materials and on their catalytic activity for the hydroisomerization of alkanes

Roldán

Beale²,

Sánchez‐Sánchez

et al. 2008

Journal of Catalysis

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A series of mono-and bi-metallic (Pt and/or Pd) impregnated zeolite Beta samples have been prepared, characterized using a number of experimental techniques and catalytically tested for the hydroisomerization of a mixture of light paraffins. In particular, the effect of the order of Pt and Pd impregnation on the type/structure of the metallic species of the zeolite support and on the catalytic activity has been studied. Studied samples included a zeolite Beta in which both Pt and Pd (0.5 wt% of each) were simultaneously impregnated (and subsequently calcined and reduced) and two equally metal-loaded samples where the metals were sequentially impregnated (samples Pt*-Pd/Beta and Pd*-Pt/Beta, in which Pt and Pd were impregnated first, respectively). Mono-metallic samples were also prepared for comparison. TPR, DR-UV-visible, TEM, and XAS studies confirm that the order of impregnation plays a key role in the formation of metallic particles, influencing aspects as decisive in their catalytic behavior as their size, their dispersion and their composition (e.g., mono-or bi-metallic). The initial impregnation of Pd and subsequently of Pt produces a higher number of hetero-metallic (Pt-Pd) bonds than the simultaneous co-impregnation and especially for the impregnation in reverse order, which does not produce Pt-Pd bonds in a detectable amount. Based on the results from the different characterization techniques, a model of the metal distribution and composition of the particles was proposed for each bi-metallic sample. In good agreement, the order of the catalytic activity was found to be Pd*-Pt/Beta > Pd-Pt/Beta > Pt/Beta > Pt*-Pd/Beta > Pd/Beta, making clear that not only the presence of both metals, but also an adequate preparation method generating a high number of hetero-metallic bonds must be taken into account to improve the catalytic properties in relation to the mono-metallic samples.

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“…Considering that branched-chain alkanes posses the greatest octane numbers, the use of gasoline containing higher content of these compounds is one alternative to obtain a fuel with the above characteristics 1,2 . Usually, they are obtained by isomerization reactions employing bifunctional catalysts formed by platinum supported over acid zeolites [3][4][5][6][7][8][9][10][11] . In view of the relative high costs of the platinum catalysts, the aim of this work is to compare the properties of bifunctional catalysts formed by Ni, Pt and Ni + Pt supported in an ultrastable Y molecular sieve (HUSY).…”

Section: Introductionmentioning

confidence: 99%

Characterization of Pt/HUSY and Pt-Ni/HUSY catalysts by transmission electron microscopy

et al. 1999

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Bifunctional catalysts formed by metals (nickel, platinum as well as an association of both metals) supported in an ultrastabilized Y molecular sieve (USY) were prepared. The samples were obtained using a competitive ion exchange method, followed by calcination and reduction of the transition metal under hydrogen atmosphere. The solids were characterized by ICP for their chemical composition, XRD, TEM and the catalytic properties evaluated in the isomerization of the n-hexane.It was observed that the NH4USY zeolite support presented better ion exchange efficiency in comparison to that of the zeolite HUSY, due to the decrease of the pH of the reaction medium in the last case. The TEM images of the catalysts, obtained in both bright and dark field, showed that the metal particles are dispersed almost inside the molecular sieve micro and mesopores. TEM images of the catalysts obtained in bright field showed that the average particle diameter were 64 and 108 Å for platinum and nickel respectively and about 70 Å when both metals are present.In the mentioned reaction, platinum catalysts were more active and stable than the nickel ones and the catalysts formed by both metals (0,2%Pt + 0,8% Ni/HUSY) presented the highest activity.

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Kinetics of Hydro-isomerization ofn-Hexane over Platinum Containing Zeolites

Cited by 93 publications

References 28 publications

The Shape Selectivity of Paraffin Hydroconversion on TON-, MTT-, and AEL-Type Sieves

The Shape Selectivity of Paraffin Hydroconversion on TON-, MTT-, and AEL-Type Sieves

Effect of the impregnation order on the nature of metal particles of bi-functional Pt/Pd-supported zeolite Beta materials and on their catalytic activity for the hydroisomerization of alkanes

Characterization of Pt/HUSY and Pt-Ni/HUSY catalysts by transmission electron microscopy

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