Mechanistic aspects of n-paraffins hydrocracking: Influence of zeolite morphology and acidity of Pd(Pt)/ZSM-5 catalysts

Meng, Lingqian; Vanbutsele, Gina; Pestman, Robert; Godin, Andreas; Romero, Douglas; Hoof, Arno J. F. van; Gao, Lu; Kimpel, Tobias F.; Chai, Jiachun; Martens, Johan A.; Hensen, Emiel J. M.

doi:10.1016/j.jcat.2020.06.031

Cited by 28 publications

(19 citation statements)

References 47 publications

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“…The more open texture of the nanocrystalline zeolites results in shorter residence time in the micropores as a consequence of the higher rate of desorption from the acidic zeolite, overall increasing the balance between hydrogenation and cracking and thus the isomer yield. [51] Notably, as compared to the three bulk samples, Pt/MOR-NO 3 + CTA shows higher isomer yields that are still much lower than observed for the other two nanocrystalline samples. Considering that Pt/MOR-NO 3 + CTA has a substantially lower external surface area than Pt/MOR-Cl + CTA and Pt/MOR-OH + CTA, the low isomer yield of Pt/MOR-NO 3 + CTA is likely due to the lack of external acid sites.…”

Section: Hydroconversion Of N-hexadecanementioning

confidence: 79%

“…The best performing samples are Pt/MOR‐Cl+CTA and Pt/MOR‐OH+CTA with isomer yields of 28.4 % and 25.4 % at conversion levels of 60.3 % and 62.6 %, respectively. The more open texture of the nanocrystalline zeolites results in shorter residence time in the micropores as a consequence of the higher rate of desorption from the acidic zeolite, overall increasing the balance between hydrogenation and cracking and thus the isomer yield [51] …”

Section: Resultsmentioning

confidence: 99%

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Synthesis of Nanocrystalline Mordenite Zeolite with Improved Performance in Benzene Alkylation and n‐Paraffins Hydroconversion

Poll

et al. 2022

ChemCatChem

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Nanocrystalline mordenite (MOR) zeolites were hydrothermally synthesized in a single step with commercial cetyltrimethylammonium (CTA) hydroxide as the sole organic template, while the aluminum source was varied in a typical synthesis gel. CTA can effectively reduce the crystal growth of MOR zeolites, in some cases selectively in the a‐ and b‐directions of the unit cell. These nanocrystalline MOR zeolites do not only have a larger external surface area than their bulk counterparts prepared without CTA, but the Brønsted acid sites in the side‐pockets are also more accessible. The combination of the use of CTA and AlCl3 ⋅ 6H2O afforded the best‐performing catalyst with much improved activity in benzene alkylation and hydroconversion of n‐hexadecane (n‐C16). Modifying MOR synthesis with CTA hydroxide is a cheap and effective method to open up the one‐dimensional micropore system of mordenite, increasing the catalytic performance in hydrocarbon reactions.

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Section: Hydroconversion Of N-hexadecanementioning

confidence: 79%

Section: Resultsmentioning

confidence: 99%

Synthesis of Nanocrystalline Mordenite Zeolite with Improved Performance in Benzene Alkylation and n‐Paraffins Hydroconversion

Poll

et al. 2022

ChemCatChem

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“…The rearrangement of this cationic intermediate drives the generation of structural isomers passing by a cyclic iso-alkylcarbenium ion intermediate and then the cracked products can be generated by β-scission. 27 The shape selectivity of a zeolite drives the location of the positive charge along the linear chain and thus the positional selectivity of chain branching or breaking. 62 The steric limitations imposed by a zeolitic lattice, combined with the distribution of the active sites, stabilizes specific conformation of the alkylcarbenium ion intermediates, thus reflecting in the selectivity for specific isomers and cracked products.…”

Section: Resultsmentioning

confidence: 99%

“…The acidic Brønsted site can protonate the alkene forming an alkylcarbenium ion. The rearrangement of this cationic intermediate drives the generation of structural isomers passing by a cyclic iso-alkylcarbenium ion intermediate and then the cracked products can be generated by β-scission . The shape selectivity of a zeolite drives the location of the positive charge along the linear chain and thus the positional selectivity of chain branching or breaking .…”

Section: Resultsmentioning

confidence: 99%

“…For this purpose, after a careful analysis of the size and volume of the different pore families by applying the non-localized density functional theory (NLDFT) model to nitrogen physisorption isotherms, different molecules with various steric hindrance and basic characters have been selected as probes. − Such information has been merged with the results obtained by employing the material as the catalyst in n -decane hydroconversion. The so-called “decane test” represents a powerful “characterization” technique for disclosing the inner space of a zeolitic material, through the evaluation of isomerization and cracking products during the conversion pathways. For comparison, the same multitechnique characterization approach has been carried out on two reference materials (an aluminum containing MCM-41 as a mesoporous model and a commercial ZSM-5 as a microporous reference) finally allowing the indirect evaluation of the internal and external map of the porous network of this complex and unique molecular sieve.…”

Section: Introductionmentioning

confidence: 99%

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Insights on a Hierarchical MFI Zeolite: A Combined Spectroscopic and Catalytic Approach for Exploring the Multilevel Porous System Down to the Active Sites

Airi

Signorile

Bonino

et al. 2021

ACS Appl. Mater. Interfaces

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The hierarchization of zeolites to overcome the major drawbacks related to molecular diffusion limitation in micropores is a popular concept in heterogeneous catalysis. Despite the constant increase of new synthesis strategies to produce such hierarchical systems, the deep knowledge of their structural arrangement and how the zeolitic lattice is organized in a multilevel porous system is often missing. This information is essential to design a structure, tuning the porosity and the distribution of easily accessible active sites, and successively controlling the catalytic properties. In the present work, the synthesis of one of the most sophisticated forms of the hierarchical ZSM-5 zeolite has been reproduced, obtaining two multilevel porous materials with different crystallinity degrees, with the final aim of investigating and clarifying the finest features of their active sites. For this purpose, an extended characterization step by means of a unique multitechnique approach has been performed, thus revealing the active site nature, abundance, and distribution. IR spectroscopy with different molecular probes and a targeted catalytic test based on the hydroconversion reaction of n-decane were the toolbox for disclosing how the MFI lattice takes part in the hierarchical structure and how it, working in synergy with the mesoporous system, confers to this material a totally new shape−size selectivity. Merging the information obtained for the synthesized hierarchical zeolite with the characterization results of two reference materials (a mesoporous aluminum-containing MCM-41 and a microporous commercial ZSM-5), it was possible to define an internal and external map of the pore network of this complex and unique molecular sieve, where strong Brønsted acidic sites are located at the mouth of the MFI micropores and, at the same time, exposed at the surface of the mesoporous channels. Hence, the possibility of easily releasing bulky products is ensured and the application possibilities of the MFI lattice are expanded beyond cracking reactions.

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Characterization and Hydroisomerization Performance of Mg‐Promoted, Pt/ZSM‐23‐Based Catalysts

et al. 2022

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The effect of Mg on the acidic and metal functions in Pt/ZSM‐23 catalysts has been studied, using both pure zeolite (Z) and preshaped ZSM‐23/Al2O3 composite (ZA) and varying the content and method of Mg loading. N2 physisorption, CO chemisorption, H2/O2 titration, XRD, TEM, TPR, and FTIR were employed to characterize the phase composition, textural and acidic properties, platinum location and dispersion. The shaping procedure used left the acidity of the parent zeolite virtually intact, while Pt dispersion on the composite support was greatly increased. Despite the increased CPt/CH+ ratio, the Pt/ZA catalyst underperformed Pt/Z in the yield of branched isomers produced in n‐decane hydroconversion. Irrespective of the support, its impregnation with Mg allowed tuning the surface acidity and improving the isomerization selectivity above the level characteristic of unpromoted Pt/Z. However, the addition of Mg through ion‐exchange resulted in an opposite effect on the catalyst selectivity. Possible reasons of such a complex behavior are discussed.

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Mechanistic aspects of n-paraffins hydrocracking: Influence of zeolite morphology and acidity of Pd(Pt)/ZSM-5 catalysts

Cited by 28 publications

References 47 publications

Synthesis of Nanocrystalline Mordenite Zeolite with Improved Performance in Benzene Alkylation and n‐Paraffins Hydroconversion

Synthesis of Nanocrystalline Mordenite Zeolite with Improved Performance in Benzene Alkylation and n‐Paraffins Hydroconversion

Insights on a Hierarchical MFI Zeolite: A Combined Spectroscopic and Catalytic Approach for Exploring the Multilevel Porous System Down to the Active Sites

Characterization and Hydroisomerization Performance of Mg‐Promoted, Pt/ZSM‐23‐Based Catalysts

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