Isomerization Reactions Research Articles

NHC-Au-Catalyzed Isomerization of Propargylic B(MIDA)s to Allenes and Double Isomerization of Alkynes to 1,3-Dienes.

The synthesis of allenyl boronates is an important yet challenging topic in organic synthesis. Reported herein is an NHC-gold-catalyzed 1,3-H shift toward allenyl boronates synthesis from simple propargylic B(MIDA)s. Mechanistic studies suggest dual roles of the boryl moiety in the reaction: to activate the substrate for isomerization and at the same time, to prevent the allene product from further isomerization. These effects should be a result of α-anion stabilization and α-cation destabilization conferred by the B(MIDA) moiety, respectively. The NHC-Au catalyst, which is commercially available, is also found to be reactive in alkyne-to-1,3-diene isomerization reactions in an atom-economic and base-free manner.

Segregation disrupts the Arrhenius behavior of an isomerization reaction.

Coexistence of segregation and interconversion or isomerization reaction among molecular species leads to fascinating structure formation in the biological and chemical worlds. Using Monte Carlo simulations of the prototype Ising model, we explore the chemical kinetics of such a system consisting of a binary mixture of isomers. Our results reveal that even though the two concerned processes are individually Arrhenius in nature, the Arrhenius behavior of the isomerization reaction gets significantly disrupted due to an interplay of the nonconserved dynamics of the reaction and the conserved diffusive dynamics of segregation. The approach used here can be potentially adapted to understand reaction kinetics of more complex reactions.

Enhanced hydroconversion of polyethylene via dual-functional catalysis: Exploiting ZSM-22 pore-mouth catalysis and Ru electronic effect

The subject of extensive research, the low-temperature hydrocracking of polyethylene reveals the one-step synthesis of iso-alkanes via metal–acid bifunctional catalysis as an emerging strategy. Zeolites, with their superior compatibility with existing petrochemical infrastructure, serve as the acidic supports of choice. In this research, Ru nanoparticles were loaded onto ZSM-22, a zeolite known for its effective pore-mouth catalysis. Mechanical ball milling enhanced the pore-mouth area and the proximity of metal–acid sites, significantly boosting the hydrocracking reaction. The electronic properties of Ru were modified by selecting various Ru precursors and adjusting loading amounts. In-situ infrared studies showed the detachment of olefin intermediates from Ru sites as a critical factor in controlling hydrocracking and the terminal hydrogenolysis reactions. By combining catalyst characterization with reaction barrier calculations from density functional theory (DFT), it was found that oxidized Ru species aid in the release of olefin intermediates, facilitating Brønsted acid-driven β-scission and isomerization reactions. The study achieved a liquid-phase yield exceeding 82 wt% and an iso/n ratio surpassing 60% under low-energy consumption conditions using commercially available catalysts.

Double 1,2‐Carbon Migration at Mixed Heavier Sn=Ge Vinylidenes

Abstract1,2‐migration is one recurring isomerization reaction in organic chemistry. In contrast, double 1,2‐migration remains rare and limited to transition‐metal complexes. Herein, we describe the synthesis, characterization and reactivity of mixed heavier Sn=Ge vinylidenes. Double 1,2‐carbon migration enables the isomerization of the stannagermenylidene (3) to the germastannenylidene (4). X‐ray diffraction analysis and DFT calculations revealed that 3 and 4 feature a Sn=Ge double bond. The reaction of 3 with IMe4 (1,3,4,5‐tetramethylimidazoline‐2‐ylidene) results in the electron redistribution in the Sn=Ge core to give the germylone‐stannylene adduct (5). Moreover, treatment of 3 with 0.25 equiv. of (AlCp*)4 produces the heteronuclear aluminyl stannagermyne (6).

Double 1,2-Carbon Migration at Mixed Heavier Sn=Ge Vinylidenes.

1,2-migration is one recurring isomerization reaction in organic chemistry. In contrast, double 1,2-migration remains rare and limited to transition-metal complexes. Herein, we describe the synthesis, characterization and reactivity of mixed heavier Sn=Ge vinylidenes. Double 1,2-carbon migration enables the isomerization of the stannagermenylidene (3) to the germastannenylidene (4). X-ray diffraction analysis and DFT calculations revealed that 3 and 4 feature a Sn=Ge double bond. The reaction of 3 with IMe4 (1,3,4,5-tetramethylimidazoline-2-ylidene) results in the electron redistribution in the Sn=Ge core to give the germylone-stannylene adduct (5). Moreover, treatment of 3 with 0.25 equiv. of (AlCp*)4 produces the heteronuclear aluminyl stannagermyne (6).

Liquid-phase hydrogenation of sunflower oil over platinum and nickel catalysts: Effects on activity and stereoselectivity

This study presents the results of comparative hydrogenation of sunflower oil over a platinum catalyst supported on activated diatomite and an industrial nickel catalyst (Pricat-9910). Catalysts are characterized using physical methods, such as transmission electron microscopic, temperature programmed hydrogen desorption, Brunauer–Emmett–Teller and inductively coupled plasma atomic emission spectrometry, enabling the determination of the size of catalyst particles, forms of adsorbed hydrogen, and specific surface area. Depending on the process conditions, hydrogenation reaction rates on platinum catalysts have been found to be 2–5 times higher than cis-trans isomerization reaction rates. Using a nickel catalyst, the hydrogenation and isomerization rates at low temperatures (110°C-130 °C) and 0.5 MPa pressure are almost similar, while, the hydrogenation rate is 1.4–1.8 times lower than the isomerization rate at high temperatures and pressures, leading to the formation of a large number of trans isomers. The difference in catalysts selectivity may be attributed the speciation and different adsorption energies of surface hydrogen, leading to the possibility of simultaneous hydrogenation of linoleic and oleic acids on the nickel catalyst.

INVESTIGATION OF THE TRANSFORMATION OF MODEL PETROLEUM RAW MATERIALS UNDER CRACKING CONDITIONS OVER A REGENERATED SPENT HYDROTREATMENT CATALYST

The physicochemical properties and catalytic activity of regenerated spent aluminium-cobalt-molybdenum hydrotreatment catalyst have been investigated under cracking conditions in the model systems n-dodecane - toluene and decalin - toluene - n-hexane. A series of experiments to study the catalytic activity of the sample was carried out using a flow-type laboratory installation within the temperature range 430-470 °C, nitrogen pressure 1.6 MPa, liquid hourly space velocity 0.5-3.0 h-1. The directions of transformation were determined for paraffin and naphthenic hydrocarbons by means of gas chromatography - mass spectrometry. Paraffin hydrocarbons enter into cracking, isomerisation and compaction reactions. Naphthenic hydrocarbons are transformed into the products of isomerisation, dehydrogenation and compaction. Predominant dehydrogenation of decalin with the formation of naphthalene and hydrogen is observed in the system under investigation. A positive role of hydrogen in thermodestructive processing of heavy oil residues is observed due to the hydrogenation of nonlinear olefin hydrocarbons and aromatic hydrocarbon intermediates, which decreases the rate of coke formation. The corresponding reaction rate constants were calculated, and the results were analysed. Conclusions are drawn about the prospects of introducing a regenerated spent hydrotreatment catalyst into the procedure of thermodestructive processing of heavy oil residues.

Tailoring the product distribution of CO2 hydrogenation via engineering of Al location in zeolite

Even though tremendous progress has been made on modified Fischer-Tropsch synthesis (FTS) multifunctional catalyst that composed of Fe-based component and acidic zeolite H-ZSM-5 for CO2 hydrogenation into value-added chemicals, the structure-function relationship between the acidic zeolite H-ZSM-5 and product distribution is still under debate. Herein, a series of H-ZSM-5 zeolites with different Al locations and acidic properties are fabricated by varying the synthesis raw agents and conditions. After combining with the carbon-encapsulated Fe-based catalyst for alkenes synthesis from CO2 hydrogenation, aromatics are directionally produced from the ellipsoidal H-ZSM-5 with Al species mainly located at the intersection of straight and sinusoidal channels, while the main products shift to iso-paraffins for the H-ZSM-5 with pillared nanosheet morphology owing to its Brønsted acid site-rich property. The Al location in H-ZSM-5 and the corresponding acidic property are systematically investigated, and the theoretical simulations illustrate that the Al species at the intersection channels could lower the energy barrier of key aromatization step. The Al richly located at straight/sinusoidal would boost the isomerization reaction. Our work not only clarifies the structure-function relationship of acidic zeolite H-ZSM-5 in valuable chemicals synthesis from CO2 hydrogenation but also provides a novel protocol for controlled synthesis.

Synergy between Lewis acidic metal sites and silanols in Sn- and Ti-Beta for conversion of butenes by DRIFTS

The synergistic effect of Lewis acidic Sn/Ti sites and silanols in Sn- and Ti-Beta zeolites on the reaction pathways and mechanisms of the conversion of butenes was investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy. The double bond migration reaction of n-butene to cis-2-butene followed an AB–AD mechanism, in which hydrogen abstraction (AB) from the methylene group at Lewis acidic Sn/Ti sites afforded an allyl intermediate, followed by synergistic hydrogen addition (AD) on silanols. In contrast, the following cis–trans isomerization reaction between cis-2-butene and trans-2-butene, and the activation of isobutene, followed an AD–AB mechanism via hydrogen addition to the double bond of butenes on silanols, forming an alkoxyl group rather than allyl group as the intermediate owing to the absence of a methylene group in 2-butene and isobutene.

Exploration on the combustion chemistry of p-xylene: A comprehensive study over wide conditions and comparison among C8H10 isomers

Pyrolysis and oxidation of p-xylene over wide conditions were studied in this work in order to provide a comprehensive insight into the combustion chemistry of p-xylene. Concerning this goal, the pyrolysis of p-xylene was investigated in a flow reactor at pressures from 0.04 to 1 atm over the temperature range of 1000–1600 K. Key radicals, isomers and PAH products including three xylyl isomers, benzyl, xylylene isomers, styrene, benzene, fulvene, indene, naphthalene and phenanthrene, were identified and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry. The oxidation of p-xylene was studied in a jet-stirred reactor at 10 atm, 800–1300 K and equivalence ratios of 0.5–2.0 with a residence time of 0.5 s. Oxidation products were quantified by using gas chromatography combined with mass spectrometry and Fourier transform infrared spectrometry. A kinetic model for p-xylene combustion over wide conditions was developed based on our previously proposed p-xylene oxidation model and validated against the new experimental measurements in this work and literature reported experimental data, including flow reactor oxidation, laminar premixed flame, ignition delay time and laminar burning velocity. In the flow reactor pyrolysis, p-xylene mainly undergoes unimolecular decomposition to yield p-xylyl, which mainly suffers the H-loss reaction to form p-xylylene and isomerization reaction to form o-xylyl. The resonantly stabilized fulvenallenyl and benzyl radicals play an important role in the formation of bicyclic and tricyclic PAHs including indene, naphthalene, and phenanthrene. In the JSR oxidation, p-xylene is predominantly consumed via H-abstraction by oxygenated radicals such as OH, O, and HO2 forming p-xylyl, which can be oxidized by HO2 and eventually converted to p-methylbenzaldehyde. As the most abundantly produced oxygenated aromatics, further consumption of p-methylbenzaldehyde results in the formation of other observed oxygenated aromatics such as cresol, benzofuran, and benzaldehyde. The combustion chemistry of three C8H10 isomers, i.e., p-xylene, o-xylene, and ethylbenzene, were also compared in terms of pyrolysis and oxidation fuel reactivity, and PAHs formation and growth, showing remarkable fuel isomeric effects.

Kinetic study of H-abstraction and preliminary pyrolysis of n-decane in post-injection fuels

The combustion and pyrolysis process of n-decane was investigated via quantum chemical method to enhance the understanding of post-injection fuels. The hydrogen abstraction reactions were the main reactions that initiated combustion and pyrolysis of n-decane via H atoms and CH3/OH/NO2 radicals. The potential energy surface of hydrogen abstraction and preliminary pyrolysis was determined via high precision CBS-QB3 and M06–2X/6–311++G (d,p) methods. RRKM - Master Equation theory had been utilized to calculate the rate constants of isomerization and β-dissociation reactions in the temperature range of 300–2000 K. In this PES, the ε-site was the most advantageous site in contrast with others and the α-site has the highest energy barrier and was the most challenging hydrogen abstraction site. The isomerisation reactions of decyl radicals play a crucial role in the combustion and pyrolysis of n-decane at low temperature, particularly via 1,5-H shift and 2,5-H shift reaction. At high temperatures, the scission of the CC bond becomes the primary mechanism. Additionally, modified information was incorporated into the detailed model of n-decane combustion and pyrolysis. The modified model exhibited good agreement with experimental measurements of the mole fractions of various significant products in Jet-stirred reactor (JSR) experiments. The research provides a foundation for future investigations of n-decane combustion and pyrolysis support.

Ring Growth Mechanism in the Reaction between Fulvenallenyl and Cyclopentadienyl Radicals.

Recombination between resonance-stabilized hydrocarbon radicals is an important class of reactions that contribute to molecular growth chemistry in combustion. In the present study, the ring growth mechanism in the reaction between fulvenallenyl (C7H5) and cyclopentadienyl (C5H5) radicals is investigated computationally. The reaction pathways are explored by quantum chemical calculations, and the phenomenological and steady-state rate constants are determined by solving the multiple-well master equations. The primary reaction routes following the recombination between the two radicals are found to be as follows: formation of the adducts, isomerization by hydrogen shift reactions, cyclization to form tricyclic compounds, and their isomerization and dissociation reactions, leading to the formation of acenaphthylene. The overall process can be approximately represented as C7H5 + C5H5 → acenaphthylene + 2H with the bimolecular rate constant of about 4 × 10-12 cm3 molecule-1 s-1. A reaction mechanism consisting of 20 reactions, including the formation, isomerization, and dissociation processes of major intermediate species, is proposed for use in kinetic modeling.

Unveiling high-temperature oxidation kinetics of PODE2: Theoretical studies on the H-abstraction, isomerization, and β-dissociation reactions

Polyoxymethylene dimethyl ether (PODEn) is a promising fuel additive to reduce soot emissions. In this work, a theoretical study on the H-abstraction reaction from PODE2 (CH3OCH2OCH2OCH3) by the H atom and CH3 radical, as well as the subsequent isomerization and β-dissociation reactions of PODE2 radicals were carried out. The geometry optimization and frequency analysis for all the stationary points on the potential energy surfaces (PESs) were performed at the M08-HX/6-311+G(2df,2p) level of theory. Single point energies were calculated using the CCSD(T)-F12 method together with the cc-pVTZ basis set. The high-pressure limit rate constants of the H-abstraction reactions from PODE2 were determined through the multistructural canonical variational transition state theory (MS-CVT) with small-curvature tunneling (SCT) correction. The temperature and pressure dependent rate constants for the unimolecular reactions of radicals produced by the H-abstraction reactions from PODE2 were calculated by solving the energy-dependent master equation using the Tsinghua University Minnesota Master Equation (TUMME) program. For the H-abstraction channels of PODE2, reaction pathways initiated via H atom attack are more energetically and kinetically favored over those via CH3 radical within the studied temperature range. The PODE2 radicals with H atoms abstracted from CH3 and CH2 sites are denoted as PODE2A (CH3OCH2OCH2OCH2) and PODE2B (CH3OCH2OCHOCH3), respectively. For unimolecular reaction channels of PODE2A radical, with increased temperatures, the dominant reaction shifts from isomerization to the decomposition process. In the case of the PODE2B radical, the two decomposition channels are consistently preferred across all temperature ranges, resulting in a competitive relationship between them. The thermodynamic properties of PODE2 and its associated radicals were calculated using the isodesmic reaction method in conjunction with multistructural torsional partition functions. Based upon the newly calculated rate constants and existing literature models, an updated kinetic model describing PODE2 combustion chemistry is developed in this work. This model incorporates the latest findings and contributes to a more comprehensive understanding of the oxidation and auto-ignition characteristics of PODE2.

Spectroscopic Study of [Mg, H, N, C, O] Species: Implications for the Astrochemical Magnesium Chemistry.

Magnesium is an abundant metal element in space, and magnesium chemistry has vital importance in the evolution of interstellar medium (ISM) and circumstellar regions, such as the asymptotic giant branch star IRC+10216 where a variety of Mg compounds bearing H, C, N, and O have been detected and proposed as the important components in the gas-phase molecular clouds and solid-state dust grains. Herein, we report the formation and infrared spectroscopic characterization of the Mg-bearing molecules HMg, [Mg, N, C], [Mg, H, N, C], [Mg, N, C, O], and [Mg, H, N, C, O] from the reactions of Mg/Mg+ and the prebiotic isocyanic acid (HNCO) in the solid neon matrix. Based on their thermal diffusion and photochemical behavior, a complex reactivity landscape involving association, decomposition, and isomerization reactions of these Mg-bearing molecules is developed, which can not only help understand the chemical processes of the magnesium (iso)cyanides in astrochemistry but also provide implications on the presence of magnesium (iso)cyanates in the ISM and the chemical model for the dust grain surface reactions. It also provides a new paradigm of the key intermediate nature of the cationic complexes in the formation of neutral interstellar species.

Kinetics and thermodynamics of unimolecular dissociation of n-C3H7I

Abstract The present work expands previous studies on the kinetics of the n-C3H7I unimolecular decomposition and the thermodynamic properties of n-C3H7I and i-C3H7I molecules, by providing combined experimental and theoretical data on the rate constant for reaction of n-C3H7I + Ar ⇌ n-C3H7 + I + Ar, as well as thermodynamic data for iodopropane isomers, calculated based on the density functional theory. The n-C3H7I dissociation rate constant has been precisely determined in shock-tube experiments by applying atomic resonance absorption spectrometry (ARAS) at the resonance transition wavelength of atomic iodine (183.0 nm) in a temperature range from 830 to 1230 K at a pressure of 3–4 bar. The resulting expression is presented in the Arrhenius form: k 1st = 1.17 × 1013exp(−191.4 kJ mol−1/RT) (s−1). Theoretical RRKM/ME calculation of the temperature- and pressure-dependent rate constant and channel branching ratio have been based on quantum chemical calculations and were performed over a wide range of thermodynamic conditions (T = 300–2000 K, p = 10−4 to 102 bar). Additionally, the thermochemistry of the reactions of n-C3H7I dissociation and isomerization has been calculated on B3LYP/cc-pVTZ-PP level of theory. Thermodynamic data, which are provided in NASA polynomial format, are in a better agreement with the available experimental data and previous theoretical estimates.

4-Thiaproline accelerates the slow folding phase of proteins containing cis prolines in the native state by two orders of magnitude.

The cis/trans isomerization of peptidyl-prolyl peptide bonds is often the bottleneck of the refolding reaction for proteins containing cis proline residues in the native state. Proline (Pro) analogues, especially C4-substituted fluoroprolines, have been widely used in protein engineering to enhance the thermodynamic stability of peptides and proteins and to investigate folding kinetics. 4-thiaproline (Thp) has been shown to bias the ring pucker of Pro, to increase the cis population percentage of model peptides in comparison to Pro, and to diminish the activation energy barrier for the cis/trans isomerization reaction. Despite its intriguing properties, Thp has been seldom incorporated into proteins. Moreover, the impact of Thp on the folding kinetics of globular proteins has never been reported. In this study, we show that upon incorporation of Thp at cisPro76 into the thioredoxin variant Trx1P the half-life of the refolding reaction decreased from ~2 h to ~35 s. A dramatic acceleration of the refolding rate could be observed also for the protein pseudo wild-type barstar upon replacement of cisPro48 with Thp. Quantum chemical calculations suggested that the replacement of the Cγ H2 group by a sulfur atom in the pyrrolidine ring, might lower the barrier for cis/trans rotation due to a weakened peptide bond. The protein variants retained their thermodynamic stability upon incorporation of Thp, while the catalytic and enzymatic activities of the modified Trx1P remained unchanged. Our results show that the Pro isostere Thp might accelerate the rate of the slow refolding reaction for proteins containing cis proline residues in the native state, independent from the local structural environment.

One-Step Green Synthesis of Isoeugenol Methyl Ether from Eugenol by Dimethyl Carbonate and Phase-Transfer Catalysts.

In this paper, the green synthesis of isoeugenol methyl ether (IEME) from eugenol by O-methylation and isomerization is completed using a one-step green process. In the methylation reaction, dimethyl carbonate (DMC) was used as a green chemistry reagent instead of the traditional harmful methylation reagents, in accordance with the current concept of green chemistry. The phase transfer catalyst (PTC) polyethylene glycol 800 (PEG-800) was introduced into the isomerization reaction to break the barrier of difficult contact between solid and liquid phases and drastically reduce the reaction conditions by shortening the reaction time and reducing the alkalinity of the reaction system. The catalytic systems for the one-step green synthesis of IEME were screened, and it was shown that the catalytic system "K2CO3 + PEG-800" was the most effective. The effects of reaction temperature, n(DMC):n(eugenol) ratio, n(PEG-800):n(eugenol) ratio, and n(K2CO3):n(eugenol) ratio on eugenol conversion, IEME yield, and IEME selectivity were investigated. The results showed that the best reaction was achieved at a reaction temperature of 140 °C, a reaction time of 3 h, a DMC drip rate of 0.09 mL/min, and n(eugenol):n(DMC):n(K2CO3):n(PEG-800) = 1:3:0.09:0.08. As a result of the conversion of 93.1% of eugenol to IEME, a yield of 86.1% IEME as well as 91.6% IEME selectivity were obtained.

Effect of Residence Time and Carrier Gas on the Dehydrogenation of n-Hexane over Alumina-supported Chromium Catalyst

CrOx/γ-Al2O3 catalyst was prepared by incipient wetness impregnation method, and the influence of residence time and carrier gas on the dehydrogenation of n-hexane were studied. It is found that n-hexane dehydrogenation over CrOx/γ-Al2O3 catalyst with H2 as carrier gas exhibits totally different catalytic behaviors with that of diluting n-hexane with N2. When diluting feed with N2, the selectivity to dehydrogenation product is promoted while the cracking reaction is exhibited with reducing residence time. However, the selectivity to dehydrogenation product is significantly decreased while the isomerization of n-hexane is promoted when using H2 as carrier gas. It is proposed that H2 undergoes dissociation on the dehydrogenation active site, and further facilitates the olefinic dehydrogenation products to form carbocation, which performing isomerization reaction on the acid site on the γ-Al2O3 surface. Therefore, the isomerization of n-hexane is promoted in cost of the selectivity to dehydrogenation product when using H2 as carrier gas.

Theoretical study on iso‐pentanol oxidation chemistry: Fuel radical isomerization and decomposition kinetics and mechanism development

AbstractThis study undertakes a detailed theoretical investigation into the iso‐pentanol radical isomerization and decomposition kinetics and the mechanism development of the iso‐pentanol oxidation. The CCSD(T)/CBS//M08‐HX/6‐311+G(2df,2p) method was adopted to calculate the reaction potential energy surface. The reaction rate coefficients were calculated by variational transition state theory (VTST) with multistructural torsional (MS‐T) partition function and small curvature tunneling (SCT) correction. Moreover, the pressure‐dependent rate coefficients were determined using the system‐specific quantum Rice‐Ramsperger‐Kassel theory (SS‐QRRK). The variational and tunneling effects were discussed, and the dominant reaction channels were identified. It reveals that the isomerization reactions play a significant role at low temperatures, while the decomposition reactions dominate the high‐temperature regime. Notably, the quantitative rate expressions for iso‐pentanol radical decomposition reactions were also obtained. Furthermore, a new kinetic model incorporating the calculated rate coefficients was constructed, exhibiting satisfactory prediction performance on ignition delay times and improved predictive accuracy of species mole fractions. This work provides accurate rate data of isomerization and decomposition kinetics and contributes to a more comprehensive understanding of the iso‐pentanol oxidation mechanism.

Influence of intracrystalline diffusion constraints enhanced by channel fluctuation on zeolite catalyst performance in isomerization and aromatization

In the realm of zeolite catalysis, understanding the role of intracrystalline diffusion constraints is of paramount significance, especially in the context of isomerization and aromatization reactions. This study delves deep into the structure-performance relationships, shedding light on the profound impact of channel fluctuation on isomerization and aromatization performance. Through meticulous analysis, we scrutinized the intracrystalline diffusion constraints of olefin intermediates integral to these reactions. ZSM-5, ZSM-22, Beta, and ZSM-12 zeolites, while possessing similar crystallinity, Si/Al ratio, acidity, and diffusion path length, display distinct channel fluctuations. Insightful in situ infrared desorption experiments coupled with molecular dynamic simulations underscore that these channel fluctuations intensify the intracrystalline diffusion constraints of olefin intermediates via an entropic trapping effect. Consequently, the isomers selectivity in n-octane isomerization adopts the sequence of Pt/Al2O3-ZSM-5 < Pt/Al2O3-ZSM-22 < Pt/Al2O3-Beta < Pt/Al2O3-ZSM-12, inversely correlating with channel fluctuation. This arises from the acceleration of undesired β-scission of olefin intermediates by intracrystalline diffusion constraints accentuated by channel fluctuation, leading to cracking by-products. Contrarily, the aromatic selectivity in 1-octene aromatization mirrors the opposite trend: ZSM-5 > ZSM-22 > Beta > ZSM-12, directly associating with channel fluctuation. This owes to the augmented intracrystalline diffusion constraints fostering the cyclization and hydrogen transfer of olefin intermediates, culminating in aromatic products. This study presents an in-depth investigation into how the diffusion constraints related to channel fluctuation influence product selectivity across different zeolite catalysts, offering valuable insights for future research and application in heterogeneous catalysis.