Hydroisomerization of Heptane Isomers over Pd/SAPO Molecular Sieves: Influence of the Acid and Metal Site Concentration and the Transport Properties on the Activity and Selectivity

Höchtl, Michael; Jentys, Andreas; Vinek, H.

doi:10.1006/jcat.1999.2761

Cited by 105 publications

(73 citation statements)

References 29 publications

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“…It yields an n-C 4 /C 3 instead of an i-C 4 /C 3 product pair (28,(37)(38)(39). It occurs when there are multiple transformations at acid sites inside pores that significantly limit sorbate mobility (14,28,38,40). This happens when the hydrogenation function is insufficiently active as compared to the acid function (38,(41)(42)(43) or when the mass transport between the hydrogenating sites and the acid sites is the rate-limiting step (18,38,41,43).…”

Section: Resultsmentioning

confidence: 99%

Differences between MFI- and MEL-Type Zeolites in Paraffin Hydrocracking

Maesen¹,

Schenk

Vlugt

et al. 2001

Journal of Catalysis

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A critical evaluation of published paraffin hydroconversion data shows that MEL-type zeolites preferentially hydrocrack paraffins where two methyl groups are separated by a methylene group, whereas MFI-type zeolites prefer paraffins with geminal methyl groups (preferably at the central carbon atom). Due to this difference in hydrocracking pathway, MEL-type zeolites will hydroisomerize a higher percentage of the feed than MFI-type zeolites at low temperature, while the reverse is true at high temperature. The free energies of adsorption calculated by means of configurational bias Monte Carlo (CBMC) molecular simulations are used to explain these differences in selectivity. They show that the MEL-and MFI-type zeolites favor the formation and hydrocracking of the dimethyl paraffins that have a shape commensurate with that of their pores. They indicate that the higher paraffin hydroisomerization selectivity of the MEL-type zeolites can also be explained by their higher selectivity for adsorbing linear rather than branched paraffins at high paraffin loading. At low paraffin loading this difference in adsorption selectivity disappears. Both temperature and loading effects could resolve a disparity in the literature between n-decane and n-heptane hydroisomerization selectivity data.

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Section: Resultsmentioning

confidence: 99%

Differences between MFI- and MEL-Type Zeolites in Paraffin Hydrocracking

Maesen¹,

Schenk

Vlugt

et al. 2001

Journal of Catalysis

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“…Over these molecular sieve catalysts having mono-dimensional 10-membered ring pore channels, multi-branched isomers which are susceptible to cracking could be suppressed, thus leading to a high isomerization selectivity. For bi-functional catalysts, acidity is one of the key factors in determining the catalytic activities of the catalysts [14,15]. Since SAPO-11 only possesses mild acidity [16], so Pt/SAPO-11 catalysts will exhibit lower activities than the aluminosilicate zeolite catalysts.…”

Section: Introductionmentioning

confidence: 99%

“…The acidity of the SAPO molecular sieves depends strongly on the Si content and the mechanism of Si substitution [15][16][17][18]. When Si atoms are introduced to the phosphorous sites of a theoretical AlPO 4 framework (SM2 substitution), Bronsted acid sites will be formed [16].…”

Section: Introductionmentioning

confidence: 99%

Hydroisomerization of Long-Chain Alkane Over Pt/SAPO-11 Catalysts Synthesized from Nonaqueous Media

et al. 2005

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SAPO-11 molecular sieves were synthesized from nonaqueous media. The effects of Si and Al sources as well as solvents on the catalytic performance of SAPO-11 were investigated by the hydroisomerization reaction of n-dodecane. The samples were characterized by XRD, XRF, N 2 -adsorption, SEM, NH 3 -TPD, IR-NH 3 and 29 Si CP MAS NMR. The SAPO-11 samples synthesized with tetraethoxysilane as the Si source showed higher Si incorporation contents than the SAPO molecular sieves prepared with polymeric Si sources (fumed silica and Si colloidal gel). The reaction results showed that Pt/SAPO-11 catalysts synthesized from ethylene glycol and glycerol media with the monomeric Si and Al sources (tetraethoxysilane, aluminum isopropoxide) exhibited higher catalytic activities than those catalysts with the polymeric Si or Al (pseudo-boehmite) sources, due to the larger external surface area and higher acidity of the former ones. Especially, the catalyst synthesized in an ethylene glycol medium possessed the highest catalytic activity. Over this catalyst, 88% conversion of n-dodecane was achieved at a low temperature of 250°C.

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“…5, a reaction order of 0.35 with respect to H 2 partial pressure in the n-heptane isomerization over the MoO 3 (6 h) catalyst was obtained, by plotting ln(FC) versus ln p H 2 , where F, C and p H 2 denote the flow rate of n-heptane, its conversion, and partial pressure of H 2 , respectively. It differs from the Pd/SAPO-11 catalyst [19] and the oxygen-modified molybdenum carbide catalyst [20], over which negative reaction orders for H 2 partial pressure were obtained. Comparing to classical bifunctional catalysts, the MoO x catalyst seems to possess more acidic sites active for isomerization step and less active sites with a metallic character for the dehydrogenation-hydrogenation step, if we take into account the bifunctional properties of MoO x [1].…”

Section: The Moo X Catalystsmentioning

confidence: 88%