Hydroisomerization Of N-hexane Research Articles

Pore mouth catalysis promoting n-hexane hydroisomerization over a Pt/ZSM-5 bifunctional catalyst

Pore mouth catalysis promoting n-hexane hydroisomerization over a Pt/ZSM-5 bifunctional catalyst

Pd–Pt promoted HPMo/UiO-66 acid catalyst for n-hexane hydroisomerization for higher quality and cleaner fuel production: Catalytic activity and kinetic modeling

The preparation of catalysts with adequate stability for the n-hexane hydroisomerization reaction is always a challenge in refineries. Therefore, in this work, the metal-organic framework UiO-66, heteropoly phosphomolybdic acid (HPMo), and bifunctional (Pd + Pt)/HPMo/UiO-66 samples were synthesized, characterized by experimental techniques, and tested in the n-hexane hydroisomerization reaction. As a result, the microporous (0.2%Pd+0.3%Pt)/30%HPMo/UiO-66 bifunctional catalyst exhibited an iso-hexane selectivity of 86% and n-hexane conversion of 72.1% after 36 h of reaction time. In addition, the Langmuir-Hinshelwood model was used to examine the kinetics of this reaction due to the inhibitory effect of hydrogen. The results provided an acceptable fit to the experimental data and allowed the determination of the kinetic parameters. Accordingly, the apparent activation energy of this bifunctional catalyst and the adsorption heats of hydrogen and n-hexane were calculated at 26.27, −16.12, and −7.82 kJ mol−1, respectively.

Metal particle size effects over the Ni/SAPO-11 bifunctional catalyst

The prominent size effects of metal nanoparticles (NPs) are mainly reflected in the change of electronic and geometric properties, which may induce distinct catalytic performance of the catalyst. Herein, Ni/SAPO-11 bifunctional catalysts with controllable sizes of Ni NPs were synthesized to investigate the particle size effects in n-hexane hydroisomerization. The results show that decreasing Ni particle size from 11.7 to 5.3 nm increases the concentration of surface Ni atoms and the proportion of low-coordinated Ni sites (corner, step sites) by 1.7 and 1.5 times, respectively. The low-coordinated surface Ni atoms have rich dangling bonds and high surface energy, resulting in greatly improved H2 adsorption and activation abilities. Moreover, an increased proportion of low-coordinated Ni sites within the Ni cluster shifts the d-band center upward, further enhancing the adsorption and activation of reactants. The intrinsic catalytic activity (turnover frequency) of 5.3 nm Ni NPs is ca. 2 times as much as that of the 11.7 nm ones. Besides, the smaller Ni NPs enhanced the metal–acid synergy, leading to a higher selectivity to isomers. This work provides deep insights into the metal particle size effects over the bifunctional Ni/SAPO-11 hydroisomerization catalysts and can be extended to various metal supported catalysts.

Hydroisomerization of n-hexane over metal oxides-loaded fibrous silica catalyst for cleaner fuel production

Fibrous silica (KCC-1) was impregnated with cobalt (Co), iron (Fe), and zinc (Zn) oxides which are denoted as Co/KCC-1, Fe/KCC-1 and Zn/KCC-1 for hydroisomerization of n-hexane. The characterization analysis revealed that the introduction of Co, Fe, and Zn into KCC-1 significantly altered the physicochemical properties of KCC-1 including reduced surface area, pore volume as well as crystallinity. Pyridine adsorbed IR showed that higher amount of the Lewis acid sites (LAS) and Brønsted acid sites (BAS) when introduced the Co, Fe, and Zn into KCC-1. Interestingly, a new band at 1610 cm−1 of Zn/KCC-1, corresponds to the presence of LAS by the formation of binuclear species of Zn in the form of [ZnOZn]2+. The formation of [ZnOZn]2+ was further confirmed by the presence of a band at 350 nm and higher intensity of the binding energy at 1022.8 eV from UV-DRS and XPS analysis, respectively. From temperature-programmed reduction analysis, these binuclear species were formed at a higher temperature, which has a stronger interaction with the KCC-1. The proposed formation of [ZnOZn]2+ was also discussed in this work. Based on the n-hexane hydroisomerization, the Zn/KCC-1 possessed the most excellent catalytic performance amongst the catalysts owing to the existence of the binuclear species of [ZnOZn]2+, which acts as a new acidic center in the stabilization of generated protonic acid sites by trapping of electrons, resulting in increased isomers yield of n-hexane as well as no cracking products. Zn/KCC-1 showed the lowest activation energy compared to other catalysts within 423–673 K.

Improved Stabilization of Sulfated Zirconia by Molybdenum: Synergy of Metal Sites and Acid Sites in the n-Hexane Hydro-Isomerization

Improved Stabilization of Sulfated Zirconia by Molybdenum: Synergy of Metal Sites and Acid Sites in the n-Hexane Hydro-Isomerization

N-HEXANE HYDROISOMERIZATION ON INDUSTRIAL NICKEL-CONTAINING CATALYSTS

In this work, we studied the process of hydroisomerization of n-hexane on various industrial nickel-containing catalysts. Ni/diatomaceous earth and NiCr2O3, which were not previously used in the isomerization process, but were used in various industrial processes, were used as catalysts in this process. For comparative purposes, the studies varied the hydrogen to feed ratio to varying degrees and calculated the conversion and isomer yield on both catalysts, which are key process indicators. On the basis of the studies performed, the optimal mode of the n-hexane hydroisomerization process on the studied catalysts was selected. Keywords: hydroisomerization, n-hexane, nickel-containing catalysts, yield of isomers, conversion

The direct synthesis of Ni/SAPO-11 hydroisomerization catalyst via a novel two-step crystallization strategy

The Ni/SAPO-11 catalyst used for n-hexane hydroisomerization was prepared via a novel two-step crystallization strategy. It involves introduction of nickel salt into the pre-crystalized system of SAPO-11 by grinding followed by a second crystallization step. No extra solvent is introduced during the whole synthesis procedure which reduces waste liquid emissions significantly. More importantly, interaction between nickel and support is effectively regulated by the novel method to achieve a well dispersed nickel species and inhibit formation of inert nickel spinel simultaneously. Chemical environments of framework Si are tuned to enhance surface acidity of the Ni/SAPO-11 catalyst. It also shows smaller particle size which favors fast diffusion of reactants and products. Insights into the two-step crystallization indicate that accumulation of SAPO-11 precursors in the pre-crystallization stage, pH regulation by nickel salt and structural directing effect of Ni2+ during the second crystallization period account for the rapid crystal growth and smaller particle size of the Ni/SAPO-11 catalyst. All the unique features endow the Ni/SAPO-11 catalyst higher activity and isomers selectivity than the Pt/SAPO-11 catalyst in n-hexane hydroisomerization.

Influence of the development of a system of nanoscale pores in a mordenite-containing rock on its selectivity for di-branched products of n-hexane hydroisomerization

Influence of the development of a system of nanoscale pores in a mordenite-containing rock on its selectivity for di-branched products of n-hexane hydroisomerization

Ligand assistance via solid-state coordination for promoting nickel dispersion over the Ni/Beta hydroisomerization catalyst

Hydroisomerization of alkanes is a vital process to improve cold flow properties of lubricant oil and increase octane number of gasoline in petrochemical industry. Non-noble metal catalysts used in this process always suffer from low metal dispersion due to weak interaction between metal species and support. Herein, density functional theory (DFT) calculations show that Ni2+ prefers to coordinate with two carboxyl oxygen of glycine in the absence of water. It makes the amino groups well exposed, forming strong interaction between the nickel-complex and aluminum groups over Beta zeolites. In contrast, Ni2+ coordinates with amino nitrogen and one of carboxyl oxygen of glycine in the presence of water. This structure has weaker interaction with support due to the absence of exposed amino groups. Based on the DFT results, a solid-state ligand assistance strategy was developed to increase metal dispersion over the Ni/Beta catalyst. UV-vis, XPS and FTIR characterization results match well with the DFT results and confirm the strong interaction between the nickel-complex and support in the absence of water. The Ni/Beta catalyst has smaller particle size of nickel oxide (0.8 nm) than that of the catalyst prepared by liquid-state ligand assistance method (5.1 nm). With increasing metal dispersion, the Ni/Beta outperforms the counterpart by liquid-state ligand assistance method and exhibits comparable isomers yield to commercial Pt catalysts in n-hexane hydroisomerization. This work provides a promising approach to boost metal dispersion on catalysts.

The effect of the nanoscale intimacy of platinum and acid centres on the hydroisomerization of short-chain alkanes

This study analyses the effect of the nanoscale intimacy of Pt metal and Brønsted acid sites on the hydroisomerization of n-pentane and n-hexane using a series of zeolite/binder composite catalysts with Pt located outside or inside of the zeolite crystal and with Pt dispersed in the zeolite crystal and its vicinity on the binder. Analysis of the conversions of n-pentane and n-hexane to branched isomers and Cn≤4 byproducts under the relevant conditions of the process showed that the highest activity is obtained for catalysts with high proximity of acid and Pt sites dispersed in the zeolite crystal together with Pt on the binder surrounding the zeolite crystals. Such an arrangement allows the hydrogenation/dehydrogenation of alkanes in close proximity to the Brønsted sites, allowing the full functionality of acid sites and limiting the diffusion of intermediate alkenes between Pt sites.

Mercaptosilane-assisted synthesis of highly dispersed and stable Pt nanoparticles on HL zeolites for enhancing hydroisomerization of n-hexane

Pt/HL-SH catalysts were synthesized by a facile mercaptosilane-assisted in situ synthesis approach and exhibited better catalytic performance in n-hexane hydroisomerization.

Kinetics of n-hexane hydroisomerization over HZSM-5 supported platinum catalysts. Features of the process mechanism and the Ni-promoting effect

• Bimetallic platinum-containing zeolites are effective catalysts for the paraffins isomerization • The presence of Ni in Pt/HZSM-5 reduces the particle size of the active phase and its stability • The introduction of Ni into Pt/HZSM-5 significantly increased the rate of hydroisomerization • The mechanism of hydroisomerization of n-hexane assumes the direct participation of hydrogen in the skeletal rearrangement • The increase in the rate of isomerization of n-hexane from the hydrogen content is close to linear Kinetic studies of the hydroisomerization of n-hexane under stationary and non-stationary conditions for Pt/HZSM-5 catalysts promoted and non-promoted with nickel have been carried out. The catalysts were studied by the low-temperature N 2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, TPR-H 2 , and TPD-NH 3 methods. It is found that the kinetic equation of n-hexane isomerization on both catalysts is written by a common fractional-rational equation, in which the hydrogen exhibits a positive effect on the reaction rate. However, the values of the kinetic constants of the reaction on the two catalysts differ, showing the influence of the Ni additive on the catalyst properties and the reaction kinetics. The introduction of Ni into Pt/HZSM was accompanied by a decrease in the particle size of the active phase, an increase in the concentration of adsorbed hydrogen, which significantly increased the rate of hydroisomerization. In addition, the distinctive characteristics of the kinetic model of the reaction on the Pt-based and the Pd-based catalyst were elucidated.

Eco-friendly synthesis of hierarchical SAPO-11 with fluoride ions for hydroisomerization of n- hexane

To increase the yield of iso-hexane and inhibit cracking of isomers in hydroisomerization of n-hexane, hierarchical SAPO-11 was employed to prepare Pt/SAPO-11 catalysts. Hierarchical SAPO-11 was prepared with fluoride ions via an eco-friendly grinding synthesis method. Fluoride ions incorporate into zeolitic framework to form T-F (T = Al and Si) bonds and inhibit the isomorphous substitution of silicon atoms. It endows SAPO-11 intra- and inter-crystalline mesopores and decreases the amount of acid sites. A low diffusion resistance and decreased acidity of catalysts are unfavorable for a subsequent isomerization and cracking of mono-branched iso-hexane. Compared to microporous SAPO-11, catalysts with hierarchical SAPO-11 have a higher selectivity of iso-hexane at a similar conversion. It is reflected as comparable TOF n-C6 = 21.3 h −1 and TOF iso-C6 = 19.9 h −1 . Results above propose a facile and green approach to prepare SAPO-11 molecular sieves. The in-situ regulation method of Pt/SAPO-11 is a reference for other types of SAPO supported catalysts. • The regulation of Pt/SAPO-11 catalysts is achieved with fluoride ions. •Interaction between fluoride ions and zeolitic atoms is investigated. •Fluoride ions introduce mesopores and decrease the particle size of Pt in hydroisomerization catalysts.

Enhanced dispersion of nickel nanoparticles on SAPO-5 for boosting hydroisomerization of n-hexane

The nickel based bifunctional catalyst with enhanced hydroisomerization performance was developed using an in-situ solid synthesis method. It was achieved to stabilize smaller Ni active sites on SAPO-5 using ethylenediaminetetraacetic acid (EDTA) ligands. The role of EDTA ligands was clarified by controlling the molar ratio of EDTA to Ni2+ (EDTA/Ni2+) over Ni/SAPO-5 catalysts. EDTA ligands inhibited the formation of nickel aluminate spinel and aggregation of NiO species during calcination, which dispersed Ni nanoparticles in a mean size of 4.7 nm on SAPO-5. The size of Ni nanoparticles could be controlled by regulating EDTA/Ni2+ ratio in [Ni-EDTA]2- complex. The prepared catalyst exhibited high yield of isomers (54.0%) and di-branched isomers selectivity (18.0%) in the n-hexane hydroisomerization, which was approximately 2 times higher than that of the Ni/SAPO-5 catalyst without EDTA ligands at similar conversion. These results are important to propose a facile approach for the preparation of highly dispersed non-noble metal based bifunctional catalysts at a high loading.

Synthesis of Zeolite supported bimetallic catalyst and application in n-hexane hydro-isomerization using supercritical CO2

The loading of novel bi-and tri-metallic bifunctional catalysts such as Pt–Ru, Pt–Zr, and Pt–Ru–Zr over original zeolites (H-MOR and H-ZSM-5) and new cations modified zeolites (Sr-MOR, Ba-MOR, Sr-ZSM-5, and Ba-ZSM-5) by supercritical CO2 method are investigated for n-hexane isomerization. A fixed bed micro-reactor unit was used for catalytical hydro-isomerization of n-hexane at different temperature ranges (250–325 °C), H2/HC ratios of 3, 6, and 9 mol and pressure of 5 bar. The chemical and physical properties of prepared zeolite nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and thermogravimetric analysis (TGA). It is reported that the metal loaded in scCO2, results in more uniform and tiny metal nanoparticle (1.37 nm) dispersion with high stability and revealed that high loading pressure in scCO2 (280–300 bar) results in higher catalytic activity and surface area. H-MOR and H-ZSM-5 possess the maximum BET surface area of 539.21 and 403 m2/g and pore size of 90.73 and 105.06 Å respectively. The finding also revealed the maximum n-hexane conversion and selectively of about 99.10% and 32.23% for Pt–Ru/H-ZSM-5%, 93.55%, and 99.72% for Pt-Zr/H-ZSM-5, and 97% and 29.74% for Pt–Ru–Zr/H-MOR catalysts respectively at H2/HC ratio of 9 and 250–325 °C. Moreover, Pt–Ru/H-ZSM-5, Pt–Zr/Ba-ZSM-5, and Pt–Ru–Zr/Ba-ZSM-5 showed the maximum yield of 11.5% and 17.7%, 40.58% and 33.19%, and 11.5% and 9.1% of 2-methyl-pentane (2-MP) and 3-methyl-pentane (3-MP) respectively at H2/HC ratio 9 and 250–325 °C. Based on results, it is concluded that Pt–Zr catalyst over ZSM-5 showed better catalytical activity among all for n-hexane isomerization, while Pt–Ru and Pt–Ru–Zr demonstrated better hydrocracking reactions.

Controllable synthesis of SAPO-11/5 intergrowth zeolite for hydroisomerization of n-hexane

Abstract Intergrowth zeolites are always synthesized to combine advantages of each single phase. Herein, the SAPO-11/5 intergrowth zeolite with controlled AFI/AEL phase ratios was synthesized and used for the n-hexane hydroisomerization. The obtained samples were characterized by XRD, TEM, SEM, N2 adsorption-desorption, NH3-TPD and 29Si MAS NMR. The new morphology different from each single phase is obtained over the SAPO-11/5 intergrowth zeolite. It also exhibits intermediate surface acid density and pore volume between the SAPO-11 and SAPO-5. With the increased AFI/AEL ratio, more surface acid sites and larger pore volume are obtained. The SAPO-11/5 intergrowth zeolite was transformed into bifunctional catalysts (Ni/SAPO-11/5–2) by loading with 4.0 wt% Ni via the impregnation method. This novel catalyst shows improved isomers selectivity and yield than each single phase catalyst in the n-hexane hydroisomerization, which is mainly attributed to the intermediate pore structure and surface acidity. Furthermore, the Ni/SAPO-11/5–2 also illustrates higher di-branched isomers selectivity (7.7%) than the Ni/SAPO-11 (2.4%) catalyst, favoring increasing the octane number of gasoline. This work provides an alternative approach to simultaneously regulate surface acidity and pore structure for the hydroisomerization catalyst.

N-Hexane hydroisomerization over Zr-modified bicontinuous lamellar silica mordenite supported Pt as highly selective catalyst: Molecular hydrogen generated protonic acid sites and optimization

Zr-modified bicontinuous lamellar silica mordenite supported Pt catalysts were synthesized using the zirconyl chloride oxahydrate as the precursor for Zr species by the incipient wetness impregnation method. The influence of zirconium loading on the properties of Zr-modified HM@KCC-1 catalysts for n-hexane isomerization were studied. The results of XRD and lattice structure from IR study indicated that increasing zirconium loading did not change the properties of catalysts. The IR study with pre-adsorbed 2,6-dimethylpyridine as a probe molecule affirmed that increasing zirconium loading could increase the Lewis acid sites. The generation of protonic acid sites which were active in n-hexane hydroisomerization was mainly from molecular hydrogen through a hydrogen spill-over mechanism as established by in situ-IR study. The results for the catalytic testing indicated that PtZr/HM@KCC-1 catalyst was highly selective in n-hexane hydroisomerization due to abundant permanent Lewis acid sites for its promotive effect in the generation of protonic acid sites. However, the incorporation of excessive zirconium amount up to 10 wt percent loading led to a decline in the amount of protonic acid sites generated, thus reduced the hydroisomerization performance in the process. The optimum conditions for hydroisomerization of n-hexane over Pt5Zr/HM@KCC-1 were reaction temperature of 293 °C, treatment temperature of 474 °C and F/W of 502 mL/g.min with the predicted value for isomer yield of 83.9%.

One-pot synthesis of the highly efficient bifunctional Ni-SAPO-11 catalyst

Hydroisomerization of linear alkanes to branched isomers is an important petrochemical process for production of gasoline with high octane number. Non-noble metal bifunctional catalysts used in this process always suffer from low metal dispersion and poor metal-acid synergy. Herein, a facile one-pot synthesis method was used to simultaneously regulate metal particle sizes and acidity of the Ni-SAPO-11 hydroisomerization catalyst. The physicochemical properties are investigated using XANES, EXAFS, TEM/STEM, FT-IR, XPS, UV–vis and NH3-TPD. Apart from the highly dispersed nickel nanoparticles with an average diameter of 8 nm, the framework Ni2+ ions are generated via substituting framework Al3+ ions of the SAPO-11. The formed NiP-OH structures have lower deprotonation energy (DPE) than the SiAl-OH ones, contributing more and stronger acid sites to the Ni-SAPO-11 catalyst. The great metal-acid synergy including high metal to acid sites ratio (nNi/nA) and close intimacy is obtained for the Ni-SAPO-11 catalyst. The Ni-SAPO-11 catalyst outperforms the counterpart prepared by the impregnation method and exhibits comparable activity and isomers selectivity to the Pt/SAPO-11 catalyst in the n-hexane hydroisomerization.

Enhanced catalytic activity of Pt/H-ZSM-12 via alkaline post-treatment for the hydroisomerization of n-hexane

Abstract Bifunctional Pt/H-ZSM-12 catalysts with enhanced inter-mesoporosity were prepared from synthesized ZSM-12 samples by alkaline post-treatments with or without the presence of the template in the zeolite pores, ammonium ion-exchange, and impregnation with Pt(NH3)4Cl2. Different techniques, such as N2 adsorption-desorption, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), NH3 temperature-programmed desorption (NH3-TPD), and pyridine-adsorption infra-red spectroscopy (Py-IR), were used to characterize the synthesized samples. The prepared Pt/H-ZSM-12 catalysts were evaluated in the hydroisomerization of n-hexane. The results show that the template-containing ZSM-12 is a better parent for introducing abundant inter-mesopores by the alkaline post-treatment, accompanying with a better preservation of microporosity and strong acid sites, in comparison to the template-free ZSM-12 as the parent. In addition, the dispersion of Pt on the alkaline-treated zeolite is increased as well, which is also helpful to enhance the conversion of n-hexane and the selectivity for the dibranched hexanes.

Pd/HZSM-5 catalyst for n-hexane isomerization: Properties, activities, and deactivation

The activity of n-hexane isomerization with 0,8 %kl Pd/HZSM-5 was studied in a micro reactor in the temperature range of 225-325 oC at 0,1 Mpa with the molar ratio H2/ hydrocarbon of 5.92, n-hexane concentration of 9.2 %mol, GHSV 2698 h-1 at atmospheric pressure. The catalyst owned suitable acidity, reasonable reductivity, good metal dispersion, and appropiate balance between metallic and acidic functions. The catalyst had high activity but low stability. The cause of deactivation was examined via a comparison of physico-chemical properties between a fresh catalyst and a used one. There was no metal sintering. The mono-metallic catalyst performed high activity for n-hexane hydro-isomerization but less stable. Deactivation is mainly attributed to coke formation. Catalyst activity and stability were significantly improved with activity of 0,7 MPa compared to that of 0,1 MPa at elevated pressure. The catalyst Pd-Co/HZSM-5 is capable of resisting against coke, thereby exhibiting high stability at 0,1 MPa. The highly stable and active catalyst helped to form high quality products to result in environment-friendly gasoline.