Catalysts For Isomerization Research Articles

Limonene oxide isomerization: a broad study of acid catalyst effects

AbstractIn this work, a broad screening of possible catalysts for limonene oxide isomerization was performed. The catalysts included both Brønsted and Lewis acids as homogeneous or heterogeneous catalysts. The aim was to show the efficiency of different catalysts in the studied reaction and use one homogeneous (methanesulfonic acid) and two heterogeneous (zeolite beta-25, montmorillonite K10) catalysts to evaluate the influence of the acid site type on the selectivity. When the selected catalysts were used, almost total conversion up to 1 h was observed (2?50% of the catalyst was based on type, 80 °C, and 16.6 V% of the solution was limonene oxide in toluene). The strength of the acid/acid catalyst influenced the composition of the products. When a strong acid (methanesulfonic acid) was used, the products formed by dehydration (p-cymene) and isomerization of the double bond (carvenone) were detected in large amounts. Using the majority of catalysts, the main products were cis- and trans-dihydrocarvone, and the minor products were carveols and carvone. The water content of the acid catalyst strongly affected the selectivity. Limonene diol was formed as a hydration product, which decreased the selectivity for the desired products. We have described a wide spectrum of possible catalysts for limonene isomerization. Moreover, our study enables the simple choice of catalyst on the basis of the desired composition of the products.

Optimizing n-heptane isomerization: The role of copper in enhancing the catalytic activity and selectivity of Pt and Cu-Pt/montmorillonite K10 catalysts

The development of efficient catalysts for n-heptane isomerization is essential for enhancing gasoline octane numbers. In this study, Pt and Cu-Pt/Montmorillonite K10 (MMT) catalysts were prepared and evaluated to investigate the effect of copper on catalytic performance and selectivity in the isomerization of n-heptane. Comprehensive characterization techniques, including XRD, BET, FTIR, TEM, and TPR, were used to investigate the structural, chemical, and electronic properties of the catalysts. Catalytic performance was tested in a fixed-bed reactor over a temperature range of 200 °C to 450 °C, with a liquid hourly space velocity (LHSV) of 1 h−1 and an H2/n-heptane ratio of 20 mL−1. The Pt/MMT catalyst exhibited an isomerization yield of 23.5 % and a selectivity of 66.8 % at 350 °C. In contrast, the incorporation of Cu into the Pt catalyst (0.8Cu-0.1Pt/MMT) enhanced its electronic environment, resulting in a higher isomerization yield of 29.6 % and selectivity of 77.5 % at the same temperature. Additionally, the Cu-Pt/MMT catalyst demonstrated robust long-term stability, maintaining an isomer yield of approximately 28.1 % and selectivity of 75.3 % after 50 h of continuous operation at 350 °C. This study highlights the improved performance of the Cu-Pt/MMT catalyst and offers valuable insights for optimizing bimetallic catalysts in hydrocarbon isomerization applications.

Hydrodesulfurization and isomerization performance of model FCC naphtha over sulfided Co(Ni)–Mo/Y catalysts

The process of deep hydrodesulfurization (HDS) in gasoline typically results in the saturation of olefins, leading to significant reductions in octane number. In this work, Y-supported Co(Ni)–Mo catalysts that with different Ni–Co content were prepared by the incipient wetness impregnation method, the structure and properties were characterized and analyzed using HRTEM, XPS, H2-TPR, and NH3-TPD. The isomerization of 1-hexene and 1-octene as well as the HDS of thiophene were studied by using model FCC naphtha. The incorporation of Ni was found to enhance the number of MoS2 stacking layers, thereby improving the degree of sulfurization in Mo and subsequently increasing the desulfurization rate, with a maximum achieved desulfurization rate of 94.7%. When employing a Ni/Co ratio of 3:2, optimal synergy between Ni and Co is achieved, resulting in a greater presence of multi-layer stacked II-Co(Ni)MoS active phases. Additionally, appropriate Brønsted acidity levels are maintained to facilitate efficient olefin isomerization while preserving high HDS activity. As a result, the current isomerization yield stands at 58.2%(mass). These understandings shed light on the development of highly HDS and olefin isomerization catalysts.

Tuning ZSM-22 zeolite through NH4F etching enables enhanced performance and tailored product distribution in n-alkane isomerization for sustainable aviation fuels

Isomerization of n-alkane remains a significant strategy for producing high-quality sustainable aviation fuels (SAF). Improving zeolite catalyst performance and optimizing iso-product distribution to meet the SAF specification are still challenging. As the limitation mainly originated from the strict shape selectivity of the microporous zeolite structure, feasible methods were highly demanded. In this work, the NH4F etching approach was utilized to controllably regulate the framework structure of ZSM-22 zeolite, leading to the rational variation in the crystallinity, porosity, morphology, and acidity, which were closely correlated with the etching severity. Compared to the elliptical 10-membered ring micropore mouths of the parent zeolite, the micropore mouths of the etched ZSM-22 zeolite tended to be circular, as observed by HRTEM and strongly supported by Raman, realizing the regulation of zeolite structure. For n-decane isomerization, the etched catalysts exhibited a considerable increase in catalytic performance, surpassing the parent Pt/ZSM-22 catalyst and the highest isomer yield of 82.1% at the conversion of 91.4% was achieved. The optimized iso-product distribution with approximatively equal amounts of several mono-branched isomers and much higher contributions of the originally disfavored isomers was also observed due to the tuned shape selectivity and the balanced bifunctionality. This work presented an efficient method to design zeolite catalysts for linear paraffin isomerization beyond the limit set by the zeolite structure and shape selectivity that meets the strict standard specification for the freezing point of the SAF.

Roles of Brønsted-Base and Brønsted-Acid Catalysts for Glucose Isomerization into Fructose and Fructose Dehydration into 5-Hydroxymethylfurfural

Roles of Brønsted-Base and Brønsted-Acid Catalysts for Glucose Isomerization into Fructose and Fructose Dehydration into 5-Hydroxymethylfurfural

Application of Ce modified zeolite to improve the performance of cresol isomerization

This study clarifies the mechanism behind the isomerization of cresol, focusing on a shaped cerium-modified Beta zeolite. The catalysts were characterized using a series of characterization techniques, including XRD, Py-IR, XPS, and TGA. The results emphasize the pivotal role of cerium, particularly at a 5 % modification concentration, in improving catalyst acidity. The mechanism of isomerization is revealed through kinetic calculation of reversible monomolecular systems, emphasizing the significance of acid sites. TGA analysis of catalyst deactivation reveals distinctive carbon deposition patterns, with the cerium-modified zeolite displaying enhanced resistance to pore blockage through Type II carbon deposition. XPS analysis post-deactivation indicates an increased proportion of Ce3+, suggesting elevated oxygen vacancies and unsaturated chemical bonds, influencing the catalytic activity negatively. In summary, an appropriate cerium modification, especially at the 5 % concentration, strikes a balance between enhanced acidity and resistance to carbon deposition, providing valuable insights for tailoring zeolite catalysts in cresol isomerization.

Alkene Isomerization Using a Heterogeneous Nickel-Hydride Catalyst.

Transition metal-catalyzed alkene isomerization is an enabling technology used to install an alkene distal to its original site. Due to their well-defined structure, homogeneous catalysts can be fine-tuned to optimize reactivity, stereoselectivity, and positional selectivity, but they often suffer from instability and nonrecyclability. Heterogeneous catalysts are generally highly robust but continue to lack active-site specificity and are challenging to rationally improve through structural modification. Known single-site heterogeneous catalysts for alkene isomerization utilize precious metals and bespoke, expensive, and synthetically intense supports. Additionally, they generally have mediocre reactivity, inspiring us to develop a heterogeneous catalyst with an active site made from readily available compounds made of Earth-abundant elements. Previous work demonstrated that a very active homogeneous catalyst is formed upon protonation of Ni[P(OEt)3]4 by H2SO4, generating a [Ni-H]+ active site. This catalyst is incredibly active, but also decomposes readily, which severely limits its utility. Herein we show that by using a solid acid (sulfated zirconia, SZO300), not only is this decomposition prevented, but high activity is maintained, improved selectivity is achieved, and a broader scope of functional groups is tolerated. Preliminary mechanistic experiments suggest that the catalytic reaction likely goes through an intermolecular, two-electron pathway. A detailed kinetic study comparing the state-of-the-art Ni and Pd isomerization catalysts reveals that the highest activity and selectivity is seen with the Ni/SZO300 system. The reactivity of Ni/SZO300, is not limited to alkene isomerization; it is also a competent catalyst for hydroalkenylation, hydroboration, and hydrosilylation, demonstrating the broad application of this heterogeneous catalyst.

Pt-promoted mesoporous Beta zeolite catalysts for n-Hexane isomerization with enhanced selectivity to dibranched isomers

We report a facile yet effective strategy to prepare hierarchical Beta zeolite with high molecular transport effectivity in catalysis. Alkaline etching involves preferential desilication from Beta framework and collapse of microporosity. The preferential desilication from outer rim of Beta stacking faults enlarged intercrystallite mesopores, while the collapse of microporosity created cylindroid-like intracrystalline mesopore. Part of Altet with lower stability was removed during alkaline etching, leading to a decrease in acid sites density. Alkaline etching of Beta zeolite with 0.2 mol/L NaOH solution greatly improved n-hexane isomerization activity over Pt-based catalysts. The maximum yield of isohexane and dibranched isomers increased by 6.2 % and 38.6 %, respectively. The enlargement of intercrystallite mesopores and the generation of intracrystalline mesopores of Beta zeolite lowered apparent activation energy of reaction. The apparent diffusivities measurements further revealed that Pt/Beta-0.2 M showed much lower transport limitation than Pt/Beta-parent. Our findings provide a promising catalyst for industrial alkane isomerization.

A Neutral PCNHCP Co(I)-Me Pincer Complex as a Catalyst for N-Allylic Isomerization with a Broad Substrate Scope.

Earth-abundant-metal catalyzed double bond transposition offers a sustainable and atom-economical route toward the synthesis of internal alkenes. With an emphasis specifically on internal olefins and ethers, the isomerization of allylic amines has been particularly under represented in the literature. Herein, we report an efficient methodology for the selective isomerization of N-allylic organic compounds, including amines, amides, and imines. The reaction is catalyzed by a neutral PCNHCP cobalt(I) pincer complex and proceeds via a π-allyl mechanism. The isomerization occurs readily at 80-90 °C, and it is compatible with a wide variety of functional groups. The in situ formed enamines could additionally be used for a one-pot inverse-electron-demand Diels-Alder reaction to furnish a series of diversely substituted heterobiaryls, which is further discussed in this report.

Synthesis of phosphine‐tethered indenyl ruthenium complexes through c‐h bonds activation followed by C‐C bond coupling: High performance catalysts for the redox isomerization of allylic alcohols

Reactions of 3‐(2‐pyridyl)indene and 5‐methyl‐3‐(2‐pyridyl)indene with Ru(PPh3)3Cl2, generated two phosphine‐tethered indenyl ruthenium complexes {η5,κ1P‐(C5H4N‐C9H4R‐C6H4PPh2)}RuCl(PPh3) (R = H, 1; R = CH3, 2), respectively. While treatment of 3‐(6‐methyl‐2‐pyridyl)indene with Ru(PPh3)3Cl2 gave a product {η5‐(CH3C5H3N‐C9H6)}RuCl(PPh3)2 (3); 1 could further react with NaBArF4 to produce a cationic complex [{η5,κ1P‐(C5H4N‐C9H5‐C6H4PPh2)}Ru(PPh3)][BArF4] (15). When treated with NaOMe in methanol, 1 was converted into [{η5,κ1P‐(C5H4N‐C9H5‐C6H4PPh2)}RuH(PPh3)] (16). These five complexes were investigated as catalysts for redox isomerization of allylic alcohols, and 16 exhibited best catalytic activity in the presence of tBuOK, reaching quantitative yield in 5 min when α‐vinylbenzyl alcohol was used as the substrate, requiring catalyst loading of 1 mol%.

Highly efficient isomerization of glucose to fructose over Sn-doped silica nanotube

Isomerization of glucose to fructose is a fundamental and key intermediate process commonly included in the production of valuable chemicals from carbohydrates in biorefinery. Enhancement of fructose yield is a challenge. In this work, Sn-doped silica nanotube (Sn-SNT) was developed as a highly efficient Lewis acid catalyst for the selective isomerization of glucose to fructose. Over Sn-SNT, 69.1 % fructose yield with 78.5 % selectivity was obtained after reaction at 110 °C for 6 h. The sole presence of a large amount of Lewis acid sites in Sn-SNT without Brønsted acid site is one of the reasons for the high fructose yield and selectivity. Otherwise, high density of Si−OH groups in Sn-SNT can ensure the presence of Si−OH groups near the Sn sites, which is important for the isomerization of glucose to fructose, leading to the high fructose yield and selectivity. Furthermore, the Sn-SNT is recyclable.

An in-situ combo Mo-based ionic liquid and SAPO-11 catalyst for efficient biolipids hydrodeoxygenation and isomerization

The design of novel practical catalysts is critical for the blossoming of biodiesel green-energy, in which Mo-based catalysts are of particular interest. In this work, an in-situ synthesis method was proposed to obtain a combo Mo-based ionic liquid and SAPO-11 catalyst. The catalyst presents both highly dispersed MoS2 as hydrodeoxygenation active sites and acidic sites for isomerization. MoS2 with a few fine layers can be identified based on TEM images and the Brønsted acid sites are dominant based on Pyridine-IR analysis. A great performance of MoS2/C8min-15 %SA can be obtained under optimized reaction conditions with 100 % conversion of methyl palmitate, 75.0 mol% hydrodeoxygenation to n-C15-C16, and 20.5 mol % isomerization to i-C15-C16. The structure and activity of the catalyst can be retained at least for 4 cycles. Thin layers and high sulfurization, large amount of Brønsted acid sites, and suitable reaction conditions are key points to achieve a significant performance and avoid over cracking and deactivation. On basis of detected intermediates and kinetic data simulations, a complex reaction pathway was proposed and the specific k values for each elementary reaction were provided for the hydrodeoxygenation and isomerization of methyl palmitate.

Effect of H2S co-feeding on the performance of the Fe/SiO2 catalyst for isomerization and dehydrogenation of C5-monoolefin

Isoprene was obtained by dehydrogenation, involving the isomerization of 2-methyl-2-butene into 2-methyl-1-butene. Notably, isoprene was produced through the dehydrogenation following isomerization using the Fe/SiO2 catalyst in the presence of H2S.

Liquid-phase xylene isomerization on nano-sized ZSM-5.

The isomerization process of xylene in the liquid phase has garnered significant attention due to its low energy consumption and high selectivity. However, conventional ZSM-5 zeolites have exhibited significantly diminished activity in this process, primarily attributed to diffusion barriers. To address this issue, Nano-ZSM-5 zeolite was synthesized using tetrapropylammonium hydroxide (TPAOH) as a structure direct agent (SDA) and introducing silicate-1 (S-1) as a crystallization seed. The impact of OH-/SiO2 molar ratio on the sample morphology was investigated. The structure of Nano-ZSM-5 zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 physical -sorption analysis. The results demonstrate that the addition of S-1 crystal seeds enables the formation of ZSM-5 crystallites with diminutive particle sizes (∼20 nm). Furthermore, variations in the OH-/SiO2 molar ratio within the synthetic system impact crystallite aggregation, excessively high or low ratios result in severe aggregation, leading to decreased specific surface area and mesoporous volume. By optimizing the OH-/SiO2 molar ratio to 0.2, the sample exhibits exceptional dispersibility with a specific surface area of 420 m2 g-1 and a mesoporous volume extending to 0.57 cm3 g-1. When utilized as a catalyst for liquid-phase xylene isomerization, nano-ZSM-5 demonstrates superior catalytic performance compared to traditional zeolite.

A potential catalyst for α-pinene isomerization: a solid superacid

The calcination temperature affects the crystallinity of the catalyst.

Silica- and Alumina-Supported Sulfated Zirconia Catalysts for Hexane Isomerization: Effect of the Support Nature

Silica- and Alumina-Supported Sulfated Zirconia Catalysts for Hexane Isomerization: Effect of the Support Nature

Strategies for enhancing catalytic efficiency and stability of MgO-biochar catalysts in glucose isomerization to fructose

Glucose isomerization to fructose is crucial for its application in food industry and biorefinery. Herein, strategies for developing MgO-biochar catalysts to convert glucose to fructose were explored and optimized with an emphasis on the influence of synthesis method on the stability of the catalyst. Despite the favorable activity exhibited by all catalysts, the embedding of MgO on the surface, loading onto porous structures, or incorporating into a carbon framework significantly diminished the catalytic activity and stability of magnesium species. The one-step synthesis approach facilitates the uniform distribution of MgO nanoparticles on the biochar matrix, enhancing their interactions and preventing Mg leaching compared to MgO-biochar prepared through two-step methods. After optimization, fructose yield exceeding 26% and a selectivity of 91% were obtained under mild conditions of 80 ℃ for 2 h in water. In summary, the effective anchoring of MgO on the biochar exhibited dual effects for enhanced catalytic activity and stability.

Silica Functionalized with Propylsulfonic Acid as an Efficient Metal-free Catalyst for Isomerization of Longifolene to Iso-longifolene

Silica Functionalized with Propylsulfonic Acid as an Efficient Metal-free Catalyst for Isomerization of Longifolene to Iso-longifolene

Synthesis of Mg–K-biochar bimetallic catalyst and its evaluation of glucose isomerization

Highly efficient isomerization of glucose to fructose is essential for valorizing cellulose fraction of biomass to value-added chemicals. This work provided an innovative method for preparing Mg-biochar and Mg–K-biochar catalysts by impregnating either MgCl2 alone or in combination with different K compounds (Ding et al. in Bioresour Technol 341:125835, 2021, https://doi.org/10.1016/j.biortech.2021.125835 and KHCO3) on cellulose-derived biochar, followed by hydrothermal carbonization and pyrolysis. Single active substance MgO existing in the 10Mg–C could give better catalytic effect on glucose isomerization than the synergy of MgO and KCl crystalline material present in 10Mg–KCl–C. But the catalytic effect of 10Mg–C was decreased when the basic site of MgO was overloaded. Compared to other carbon-based metal catalysts, 10Mg–KHCO3–C with 10 wt% MgCl2 loading had excellent catalytic performance, which gave a higher fructose yield (36.7%) and selectivity (74.54%), and catalyzed excellent glucose conversion (53.99%) at 100 °C in 30 min. Scanning electron microscope–energy dispersive spectrometer and X-Ray diffraction revealed that the distribution of Mg2+ and K+ in 10Mg–KHCO3–C was uniform and the catalytic active substances (MgO, KCl and K2CO3) were more than 10Mg–C (only MgO). The synergy effects of MgO and K2CO3 active sites enhanced the pH of reaction system and induced H2O ionization to form considerable OH− ions, thus easily realizing a deprotonation of glucose and effectively catalyzing the isomerization of glucose. In this study, we developed a highly efficient Mg–K-biochar bimetallic catalyst for glucose isomerization and provided an efficient method for cellulose valorization.Graphical

Seed-Assisted Interzeolite Conversion Strategy for Fabricating Lewis Acid Sn-CHA Zeolites.

Small-pore Lewis acid zeolites have been showing increasing potential in shape-selective reactions regarding small-molecule conversion. In this study, Sn-CHA with tunable framework Sn contents was facilely prepared via a fluoride-free, seed-assisted interzeolite conversion (IZC) pathway. Commercially available dealuminated USY functioned as the parent sample, and seeding played a vital role in accelerating the transformation process, promoting the target zeolite yield, and guiding the attached-growth pathway. Notably, a proto-zeolite phase with a semi-constructed pore structure was captured during the IZC process, which represents a crucial intermediate stage for developing the complete CHA structure and ensuring a well-defined Sn status. The detailed synthesis mechanism was explored in multiscale by a series of techniques. The obtained Sn-CHA and proto-Sn-CHA exhibited excellent catalytic performance in converting 1,3-dihydroxyacetone to methyl lactate. Proto-Sn-CHA was proven to be a highly effective glucose isomerization catalyst owing to its larger pore size and Lewis acidic nature.