The mechanism of catalytic cracking of <i>n</i>‐alkenes on ZSM‐5 zeolite

Abbot, J.; Wojciechowski, B. W.

doi:10.1002/cjce.5450630315

Cited by 73 publications

(72 citation statements)

References 8 publications

(4 reference statements)

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“…16,17 However, these surface intermediates may not be true carbocation species, but instead alkoxide species that retain cationic character only in activated complexes during chemical reactions. [18][19][20][21][22] Mechanistic proposals for light alkane reactions on acid catalysts include hydride transfer from the alkane to an adsorbed carbenium ion (Scheme 1), [23][24][25][26] or protonation of alkenes, formed in preceding dehydrogenation steps to form a carbenium ion (Scheme 2), [27][28] or direct interaction of the alkane with a proton to form a carbonium ion, followed by H 2 desorption to form a carbenium ion (Scheme 3). 26 The relative contributions of these mechanistic routes in the initial activation of propane on H-ZSM5 can be measured using reaction mixtures of propane and propene.…”

Section: Mechanism Of Propane Activation Reactions On Bronsted Acidmentioning

confidence: 99%

Isotopic Tracer Studies of Propane Reactions on H−ZSM5 Zeolite

Biscardi

Iglesia

1998

J. Phys. Chem. B

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Reactions of 13 C-labeled alkanes show that chain growth and cyclization reactions on H-ZSM5 require the initial formation of the corresponding alkene and its extensive participation in rapid oligomerization/ -scission reactions before cyclization occurs. The role of alkene intermediates was established by the initial formation of predominantly unlabeled products from mixtures of propene and propane-2-13 C reactants. Aromatic products of propane-2-13 C reactions on H-ZSM5 contain similar fractions of 13 C-atoms and binomial isotopomer distributions. Sequential formation, rapid intramolecular isomerization, and -scission reactions of long surface chains must occur during each aromatization turnover in order to form such binomial 13 C isotopomer distributions.

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Section: Mechanism Of Propane Activation Reactions On Bronsted Acidmentioning

confidence: 99%

Isotopic Tracer Studies of Propane Reactions on H−ZSM5 Zeolite

Biscardi

Iglesia

1998

J. Phys. Chem. B

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“…These processes receive a lot of interest to selectively produce propene, by cracking less valuable C 4 through C 8 olefins [36][37][38]. Alkene cracking processes consist of a complex reaction network including isomerizations, oligomerizations, alkylations, hydride transfers and cracking reactions [3,7,39]. In any case, knowledge on the reaction intermediates is of utmost importance.…”

Section: Introductionmentioning

confidence: 99%

On the stability and nature of adsorbed pentene in Brønsted acid zeolite H-ZSM-5 at 323 K

Hajek

Mynsbrugge

Wispelaere

et al. 2016

Journal of Catalysis

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Herewith we have the pleasure to resubmit the paper entitled : "On the stability and nature of adsorbed pentene in Brønsted acid zeolite H-ZSM-5 at 323 K" by J. Hajek , J. Van der Mynsbrugge, K. De Wispelaere , P. Cnudde, L. Vanduyfhuys, M. Waroquier and V. Van Speybroeck, for publication in Journal of Catalysis.We have received the comments of two reviewers which were very positive and which suggest publication subject to some major/minor revisions. We have taken them all into account in the revised version. In separate documents we give a substantial reply to the reviewers that carefully addresses the issues raised in the reviewer's comments. We have added an author (Louis Vanduyfhuys) in the list. During the revision process he has given a very constructive contribution in a correct thermodynamic analysis of the metadynamics results. As requested by one of the reviewers, we re-analyzed all our MD results. We hope that you are willing to accept this slight change in the author list.We further hope that the manuscript is now suitable for publication. Reply to reviewer #1 :We thank the reviewer for his/her careful reading of the manuscript with manuscript number JCAT-16-151. We try to give a valuable reply to all comments which were all very constructive. Reviewer's comments are printed in blue.1. The DFT calculations have been carried out at 0 K by optimizing the geometry at the RPBE+D3 level and then conducting single point calculations with other functionals. While the general conclusions drawn from the calculations are independent of the functional chosen, it would be very useful to know whether geometry optimization with a better functional would change the conclusion about the relative stability of the -complex and alkoxide structures.The authors completely agree with the major concern of the reviewer regarding the reliability of the geometry optimization based on one level of theory (PBE+D3). This functional has proven to be reliable in many periodic static calculations on nanoporous materials, but to remove any doubt we performed new geometry optimizations and frequency calculations for 2-pentene π-complex and 2-pentoxide using BEEF-vdW functional .[1] Geometrical details of the selected structures with PBE-D3 and BEEF-vdW functionals are given in Table 1. The comparison of free energy ΔG and enthalpy ΔH differences between BEEF-vdW //PBE D3 and BEEF-vdW // BEEF-vdW is given in Table 2. The energy differences are very similar with each other, and support the conclusions made in the paper. These additional results have been included in *Revision NotesWe thank the reviewer for this remark and reformulated the sentence slightly. The origin of larger adsorption enthalpies for the -complex is indeed related to usage of optimized geometries, which take into account only one point on the potential energy surface. Our MD simulations show that in reality at finite temperatures, the -complex can adopt various geometries leading to a probability distribution as shown in Figure 3 of the main manuscript. This dis...

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“…In iso-hexene cracking, the isomerization rate is far greater than the decomposition rate and affects product distribution. It has been reported in the literature that, with the increase in the carbon chain, the isomerization rate was unchanged (Abbot and Wojciechowski, 1985), while the cracking rate increased rapidly (Kissin et al, 2001). Therefore, by using SAPO-34 as a cracking catalyst for 1-hexene, we prevent that the feed undergoes isomerization and HT reactions, with ultimately enhanced propylene selectivity.…”

Section: Impact Of Raw Materialsmentioning

confidence: 92%

Hexene catalytic cracking over 30% sapo-34 catalyst for propylene maximization: influence of reaction conditions and reaction pathway exploration

Nawaz

Tang

Wei

2009

Braz. J. Chem. Eng.

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-Higher olefins are produced as a by product in a number of refinery processes and are one of the potential raw materials to produce propylene. In the present study, FCC model feed compound was considered to explore the olefin cracking features and options to enhance propylene using 30% SAPO-34 zeolite as catalyst in a micro-reactor. The superior selectivity of propylene (73 wt%) and higher total olefin selectivity was obtained over 30% SAPO-34 catalyst than over Y or ZSM-5 zeolite catalysts. The thermodynamical constraints were found to be relatively less serious in the case of 1-hexene conversion. Most of the 1-hexene follows a direct cracking pathway to give two propylene molecules, due to weak acid sites and better diffusion opportunities. The higher temperature and short residence time could also suppress the hydrogen transfer reactions. From OPE (olefins performance envelop) the products were classified as primary, secondary, or both. Iso-hexene (2-methyl-2-pentene) cracking was also analyzed in order to justify a shape selective effect of the SAPO-34 catalyst. A detailed integrated reaction network together with an associated mechanism was proposed and discussed in detail for their fundamental importance in understanding the olefin cracking processes over

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The mechanism of catalytic cracking of n‐alkenes on ZSM‐5 zeolite

Cited by 73 publications

References 8 publications

Isotopic Tracer Studies of Propane Reactions on H−ZSM5 Zeolite

Isotopic Tracer Studies of Propane Reactions on H−ZSM5 Zeolite

On the stability and nature of adsorbed pentene in Brønsted acid zeolite H-ZSM-5 at 323 K

Hexene catalytic cracking over 30% sapo-34 catalyst for propylene maximization: influence of reaction conditions and reaction pathway exploration

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