Hydroisomerization Of N-alkanes Research Articles

Deactivation mechanism of NiWS/SAPO-11 catalyst in hydroisomerization of n-hexadecane: Insights into coke deposition behavior and active phase migration

The application of non-noble metal supported catalysts in the hydroisomerization of long-chain n-alkanes is a novel field, and there is currently not any research available on the deactivation process of these catalysts. We investigated into the deactivation mechanism of NiWS/SAPO-11 catalyst in the hydroisomerization of n-hexadecane in this work for the first time. Specifically, coke deposition behavior and active phase migration were investigated. The reduction of catalytic efficiency of the catalyst was partially aided by the decrease in specific surface area, pore volume, and acid density. From the perspective of the active phase, the clusters of NiWS active phase migrated as the reaction time increased, mostly resulting in an increase in both the stacking number and the length of active phase slabs. The migration of active phase increased the distance between active phase clusters and metal sites, and decreased the utilization ratio of active metal atoms. From the perspective of coke deposition, the coke formed on the catalyst includes soft coke and hard coke. The formation and evolution of coke on the catalyst were investigated. The soft coke (aliphatic compounds) progressively transformed into hard coke (polycyclic aromatic hydrocarbons and graphite-like), and the coke gradually migrated from the external surface of the catalyst to the pore channels as the reaction time increased. It is expected to provide theoretical basis and reference value for the deactivation research and design of non-noble metal supported hydroisomerization catalyst.

Shape selection of alkane hydroisomerization over one-dimensional zeolite supported Pt catalyst: Pt/ZSM-48 versus Pt/ZSM-22

Hydroisomerization of long-chain n-alkanes plays a vital role in petrochemical and coal chemical industries, because it can produce high-quality hydrocarbon fuels and lubricant base oils. ZSM-48 (0.56 × 0.53 nm) and ZSM-22 (0.57 nm × 0.46 nm) are characteristic of one-dimensional 10-member ring zeolites suitable for n-alkanes hydroisomerization reaction. Here, the effect of the structure difference between ZSM-48 and ZSM-22 zeolites on hydroisomerization is titrated by the isobutane and n-dodecane. The product distribution of hydroisomerization of isobutane to n-butane shows the reaction pathway on Pt/ZSM-48 and Pt/ZSM-22, in which the monomolecular hydroisomerization of isobutane is involved within the active sites in zeolite channels, while the polymerization-cracking bimolecular reaction occurs on the pore-mouth of zeolite. Pt/ZSM-48 zeolite, possessing larger channel and aperture size than those of Pt/ZSM-22, is more conducive to the diffusion of butane molecules and bimolecular polymerization. Therefore, the isobutane conversion (14 %) on Pt/ZSM-48 produces less C1+C2 (1.7 wt% vs. 3.4 wt%) and more C3+C5+C8 (19.2 wt% vs. 16.9 wt%). For the hydroisomerization of n-dodecane, the iso-dodecane selectivity of Pt/ZSM-48 (43.3 wt%) is significantly higher than that of Pt/ZSM-22 (12.4 wt%) at the similar n-C12 conversion (40 %). Compare with the isomers of Pt/ZSM-22, the mono-branched isomers with methyl near the middle of the chains and multi-branched isomers are more easily formed on Pt/ZSM-48, which is conducive to the “key-lock” catalysis mechanism. The larger pore size of ZSM-48 is conducive to n-C12 insertion into zeolite pores, methyl migration and isomer diffusion, and its adjacent pores are more compatible with double-branched isomers. In addition, a high selectivity of C4∼C5 alkanes (53.2 wt%) on Pt/ZSM-22 and a high selectivity of C6∼C9 alkanes (44.7 wt%) on Pt/ZSM-48 show obvious difference in cracking product distribution, implying different position of methyl groups in i-C12 isomers on Pt/ZSM-22 and Pt/ZSM-48 samples, respectively. The present comparison between Pt/ZSM-48 and Pt/ZSM-22 benefits the selection and development of one-dimensional zeolitesupported metal catalyst in a wide range of hydro-processing reactions.

Effect of diffusion and metal-acid synergy on catalytic behavior of the Pd/Hierarchical SAPO-31 nanoparticles for hydroisomerization of n-hexadecane

The hydroisomerization of long-chain n-alkanes proves to be an effective approach for the production of renewable second-generation biodiesel, and the development of bifunctional catalysts with synergistic effect between metal and acidic sites was the key to increase the yield of iso‐alkanes. Herein, novel hierarchical SAPO-31 nanoparticles (S31-Hi) were synthesized with varied amounts of the growth inhibitor 1-octyl-3-methylimidazolium chloride ionic liquid (OMIMCl IL) in a one-stage crystallization, and a proposed formation process was discussed. The 0.1Pd/S31-Hi bifunctional catalysts were prepared by loading only 0.1 wt% Pd based on the S31-Hi by wetness impregnation method and their catalytic performances were evaluated for the hydroisomerization of n-hexadecane. The catalytic performance of 0.1Pd/S31-H based on the S31-H synthesized by adding an appropriate amount of OMIMCl ILs was significantly improved, which can be attributed to the enhanced diffusion originating from its smaller crystal size, higher Pd dispersion, and larger CPd/CH+ value, which was beneficial for achieving synergistic catalysis. The iso‐hexadecane yield of 77.8% and proportion of multi-branched isomers of 51.5%, and catalytic stability within 100 h time on stream was obtained over the 0.1Pd/S31-H at n-hexadecane conversion of 89.3%. These catalysts have application potential for the production of second-generation clean biodiesel with excellent low temperature fluidity.

Unusual roles of ceria as the support of a single-atom catalyst in hydroisomerization of n-heptane: Phase boundary acts as transport channels between different active centers

Hydroisomerization of n-alkanes plays an important role in fuel and lubricants processing. Bifunctional catalysts with ultralow platinum loading have recently been reported successively for hydroisomerisation. Herein, the catalysts were prepared successfully with different methods to improve the catalytic performance. The conversion of 0.01%Pt1@CeOx/SAPO-11 prepared by co-calcination method (0.01%Pt1@CS-c) is 71.4%, 25% higher than the other prepared by precipitation method. The turnover frequency per active surface platinum site (TOFPt) of 0.01%Pt1@CS-c is as high as 13115 h–1. Revealed by the X-ray photoelectron spectroscopy (XPS) results, the quality of phase boundary/intersurface between ceria and zeolite is found significantly different. The conjunction quality of phase boundary directly affects the spillover rate of intermediate species, which further leads to an apparent activity difference. In addition, the possible role of ceria in the reaction is discussed, rather than just as a carrier for the active metal atoms.

Tailored synthesis of plate-like SAPO-11 molecular sieve and its application in non-noble metal-supported catalyst for efficient hydroisomerization of long-chain n-alkanes

The tailored synthesis of plate-like SAPO-11 molecular sieve was achieved by introducing seed-surfactant directing agent into the synthesis system for the first time. The effects of morphological change of SAPO-11 molecular sieve on the physicochemical properties of SAPO-11 and the active phase properties of the catalyst were analyzed via a series of characterization techniques. The hydroisomerization of n-hexadecane was used as the model reaction to evaluate the catalytic performance of NiWS supported catalysts based on SAPO-11 molecular sieve with different morphologies. The plate-like SAPO-11 possessed better textural properties and acidity than pseudo-spherical SAPO-11. Meanwhile, the stacking number, dispersion and metal sulfidation degree of the active phase of sulfided NiW/SAPO-11-P were improved, and its high proportion of type II active phase optimized the metal–acid synergistic catalytic mechanism. Through tracking and analyzing the crystallization process of plate-like SAPO-11, the formation mechanism of plate-like SAPO-11 was investigated and revealed. The adsorption kinetics, diffusion behavior and catalytic kinetics of n-hexadecane on the catalysts were emphatically investigated. The optimized support structure and active phase properties improved the intrinsic catalytic activity and hydroisomerization reaction path priority of NiW/SAPO-11-P. It was found that the hydroisomerization reaction on NiW/SAPO-11-P was carried out under the reaction-limiting conditions, while the hydroisomerization reaction on NiW/SAPO-11-C was carried out under the reaction-controlling conditions. The effects of plate-like SAPO-11 on the activity stability of the catalyst was investigated, and the essential reasons for the differences in activity stability of the catalysts were revealed through comprehensively analyzing the coke formation difference and diffusion behavior difference. It is expected to provide reference for the tailored design of SAPO-11 molecular sieve with special morphology and the preparation of efficient hydroisomerization catalyst.

The Preparation of Nanosized Pd/ZSM-23 Bifunctional Catalysts for n-Hexadecane Hydroisomerization by Employing PHMB as the Growth Modifier

The development of highly effective metal–zeolite bifunctional catalysts for the hydroisomerization of n-alkanes is a paramount strategy to produce second-generation biofuels with high quality. In this study, polyhexamethylene biguanide hydrochloride (PHMB) is precisely added to the initial gel to synthesize nanosized ZSM-23 zeolites (Z23-xPH). Due to orientation adsorption and steric hindrance effects of PHMB, each sample of Z23-xPH demonstrates enhanced mesoporosity in comparison with the conventional Z23-C zeolite. Furthermore, the Brønsted acid density of the Z23-xPH samples is also significantly reduced due to a reduction in the distribution of framework Al at T2–T5 sites. The corresponding Pd/23-C and Pd/Z23-xPH bifunctional catalysts with 0.5 wt% Pd loading for n-hexadecane hydroisomerization are prepared by incorporating ZSM-23 zeolites as acid supports. According to the catalytic test results, the suitable addition of PHMB can effectively promote the iso-hexadecane yield. The Pd/Z23-2PH catalyst with an nPHMB/nSi molar ratio of 0.002 demonstrates the highest maximum iso-hexadecane yield of 74.1% at an n-hexadecane conversion of 88.3%. Therefore, the employment of PHMB has provided a simple route for the development of highly effective Pd/ZSM-23 catalysts for n-alkane hydroisomerization.

The synthesis of hierarchical ZSM-22 zeolite with only the PHMB template for hydroisomerization of n-hexadecane

The ZSM-22 zeolite has become an effective support for the hydroisomerization of n-alkanes due to its one-dimensional pore structure, good hydrothermal stability and simple synthesis process. However, the diffusion resistance of hydrocarbons in the microporous channel still limits the further industrial application of the traditional microporous ZSM-22 zeolites. To overcome the diffusion limitation, the different amounts of polyhexamethylene biguanide (PHMB) was added into the initial gel as the only template instead of 1,6-diaminohexane (DAH) to synthesize a series of hierarchcal ZSM-22 zeolites (Z22-xP), and the corresponding Pd/ZSM-22 catalysts with 0.5 wt% Pd loading were then prepared for n-hexadecane hydroisomerization in this work. The characteristic results show that, the Z22-xP samples exhibit improved mesoporous volume and external surface than those of the traditional microporous Z22-D sample. Additionally, the Z22-xP samples also demonstrates significantly lower Brønsted acid density in comparison with the microporous Z22-D sample because of the proportion decrease of T1-T3 skeleton Al atoms. The catalytic tests results indicate that the employment of PHMB instead of DAH can effectively promote the catalytic performance. The Pd/Z22-0.002P catalyst reveals the highest iso-hexadecane yield of 76.6 % among all catalysts. Therefore, this work provides a more convenient and effective way for the development of potential bifunctional catalysts with promoted catalytic performance.

Novel construction and synthesis mechanism of b-axis oriented flower-like SAPO-11 molecular sieve in OSC-containing system for efficient hydroisomerization of long-chain n-alkanes

In view of the fact that different kinds of flower-like zeolites and materials have been synthesized for catalysis, but there are few reports on the construction of flower-like SAPO-11 molecular sieve. In this work, we successfully synthesized b-axis oriented flower-like SAPO-11 molecular sieve with multi-layered structure in the organosilicon compounds (OSC)-containing system for the first time. The morphology and b-axis thickness of SAPO-11 flakes were controlled and the tailored synthesis of b-axis oriented flower-like SAPO-11 with multi-layered structure was realized by adding [3-(trimethoxysilyl) propyl] octadecyl dimethyl ammonium chloride (DMC) into the synthesis system. The NiWS supported catalyst for hydroisomerization of n-hexadecane was prepared by using the synthesized flower-like SAPO-11 as support. Through a series of characterization techniques, the effects of morphological changes of SAPO-11 molecular sieve on the textural properties, acidity, element composition and silicon distribution of SAPO-11 molecular sieve were investigated, and the influence mechanism of morphological changes of the support on the active phase properties of the catalyst was studied. The formation mechanism of multi-layered flower-like SAPO-11 was proposed, the influence mechanism of the morphological change of the support on the catalytic performance of the catalyst and the catalytic reaction kinetics was investigated, and the structure–activity relationship between flower-like SAPO-11 and NiWS supported catalyst was systematically expounded. It provides a reference for enriching the morphological types of SAPO-11 molecular sieve and preparing catalyst for high-efficiency hydroisomerization of long-chain n-alkanes.

Novel synthesis strategy of SAPO-11 molecular sieve with superior performance for hydroisomerization of long-chain n-alkanes: Supergravity-cyclone assisted hydrothermal crystallization method

In this work, we successfully synthesized high performance SAPO-11 molecular sieve via the novel supergravity-cyclone assisted hydrothermal crystallization method for the first time. The initial gel was subjected to cyclone treatment and supergravity shearing treatment to obtain the secondary molecular sieve precursor mixture with high viscosity and micro-bubble distribution. The effects of supergravity shear-cyclone operation on the physicochemical properties of SAPO-11 molecular sieve were investigated. The supergravity-cyclone treatment improved the textural properties and acidity of SAPO-11 molecular sieve. The effects of support properties on the properties of active phase of NiWS-support catalyst and its catalytic performance for hydroisomerization of n-hexadecane were further investigated. NiW/SAPO-11-B showed more active phase with hydroisomerization kinetics advantage and nearly doubled yield of i-hexadecane compared with conventional SAPO-11-based catalyst. The process and mechanism of synthesizing high performance SAPO-11 molecular sieve via the supergravity-cyclone technology were explored. It was found that the supergravity-cyclone assisted crystallization method shortened the crystallization time of SAPO-11 and improved the crystallization efficiency. In addition, the hydroisomerization kinetics of n-hexadecane on SAPO-11-based NiWS supported catalyst was studied. The structure–activity relationship between the structure of active phase and the formation of CUS was investigated, and the influence of support properties on the properties of NiWS active phase and their synergistic mechanism in the hydroisomerization of n-hexadecane were revealed. This is expected to provide a new strategy for the synthesis of high performance SAPO-11 molecular sieve and the preparation of non-noble metal supported catalyst with superior hydroisomerization performance for long-chain alkanes.

Isomerization Properties of Pt/SAPO-11 Catalysts for the Production of Bio-Aviation Kerosene

The hydroisomerization of n-alkanes is an important step in the production of high-quality bio-aviation kerosene. A SAPO-11 molecular sieve was synthesized using the hydrothermal synthesis method, and a 0.5 wt% Pt/SAPO-11 catalyst was prepared using the impregnation method. The crystal phase, pore structure, acidity, and morphology of Pt/SAPO-11 were characterized via X-ray diffraction, N2 adsorption-desorption, NH3 temperature-programmed desorption, scanning electron microscopy, and transmission electron microscopy, respectively. The hydroisomerization performance of the catalyst was evaluated with bio-n-hexadecane as the model compound. The results showed that temperature and space velocity had significant effects. Under the conditions of 340 °C, 1.5 MPa, WHSV = 1.0 h−1, V(H2): V(n-hexadecane) = 1000:1, the conversion of n-hexadecane and the selectivity of i-hexadecane were 81.8% and 86.5%, respectively.

The effects of growth modifiers on the catalytic performance of hierarchical Pd/ZSM-23 bifunctional catalysts for n-hexadecane hydroisomerization

Hydroisomerization of n-alkanes catalyzed by metal-zeolite bifunctional catalysts is an important process to produce clean biofuels. The employment of appropriate growth modifiers during the synthesis of hierarchical zeolites to increase the iso-alkane yield has captured much attention. In this work, cetyltrimethylammonium bromide (CTAB) and polydiallyl dimethyl ammonium chloride (PDDA), representatives of cationic surfactants and cationic polyelectrolytes, are added to the initial gel to one-pot synthesize hierarchical ZSM-23 zeolites (Z23-xPC and Z23-yPP) via the bottom-up strategy. The corresponding Pd/ZSM-23 catalysts are prepared by loading 0.5 wt% Pd on microporous and hierarchical ZSM-23 and tested for the hydroisomerization of n-hexadecane. Due to the cationic adsorption of CTAB or steric hindrance effect of PDDA, Z23-xPC and Z23-yPP samples all demonstrate enhanced mesoporosity compared with the conventional microporous Z23-P sample. The diffusivity experiments indicates that the D/L2 values decrease in the order of Pd/Z23-5PP > Pd/Z23-3PC > Pd/Z23-P, suggesting that the hydrocarbons diffusion in the channel of hierarchical ZSM-23 samples is evidently improved. In addition, the Brønsted acid densities of the Z23-xPC and Z23-yPP samples are also evidently reduced compared to that of the microporous Z23-P sample because of the proportion decreases of framework Al atoms at T2-T5 sites. Compared with the microporous Pd/Z23-P catalyst, the appropriate addition amount of growth modifiers can evidently improve the yield of iso-hexadecane products and limit the cracking process. Especially for the Pd/Z23-5PP catalyst, the cracking process is effectively limited and the maximum iso-hexadecane yield of 75.4% is obtained at an n-hexadecane conversion of 88.8% at 290 °C, which is the highest among all catalysts. Therefore, this work has provided an effective method for the simple preparation of bifunctional catalysts with improved diffusion performance and more favorable metal–acid balance.

Tuning the Structure and Acidity of Pt/Hierarchical SSZ-32 Catalysts to Boost the Selective Hydroisomerization of n-Hexadecane

Developing highly selective and efficient bifunctional catalysts is an important issue for the hydroisomerization of long-chain n-alkanes. It is vital to tailor the balance of isomerization and cracking reactions in hydroisomerization. Herein, a bifunctional Pt/hierarchical SSZ-32 catalyst was fabricated with a sequential desilication–dealumination treatment to boost the selective hydroisomerization of n-hexadecane (C16). The pore structure and acid sites of SSZ-32 zeolite were tailored. More mesopore and Brønsted acid sites were generated, and the ratio of weak to strong Brønsted acidity (Bw/Bs) was increased by the sequential desilication–dealumination. The generated hierarchical structure had little effect on the selectivity of the reaction pathways of hydroisomerization versus cracking. The ratio of isomers/cracking products increased almost linearly with the increase in the Bw/Bs ratios. Meanwhile, the synergetic effect of the hierarchical structure and acidity regulation promoted the selectivity of monobranched i-C16 products. Therefore, the resulting Pt/SSZ-0.6AS exhibited the highest activity with a total isomer yield of 71.5% at 255 °C and the enhanced formation mechanism of monobranched isomers occurred via the pore mouth.

Construction of hierarchical core-shell Pt/USY@MSA bifunctional catalysts for hydroisomerization of n-hexadecane

Hydroisomerization of long-chain n-alkanes is an indispensable process in the upgrading of fuel oil and lubricants to meet the state of art regulations. In this work, a novel core-shell structural material comprising USY zeolite core and mesoporous aluminosilicate (MSA) shell, denoted as USY@MSA, was fabricated by virtue of a desilication and recrystallization approach. Comprehensive characterizations demonstrate that the USY@MSA composite exhibits a hierarchical pore architecture and a gradient acidity. Due to the confinement effect of the mesoporous aluminosilicate shell, highly dispersed platinum particles were selectively deposited on the shell, generating a nanoscale distance with acidic sites of USY zeolite core. In the hydroisomerization of n-hexadecane, the Pt/USY@MSA composite catalyst outperforms the conventional Pt/USY and desilicated Pt/USY-ds catalysts, effectively suppressing the cracking side reactions and producing higher selectivity to branched isomers.

Modulating acid site distribution in MTT channels for controllable hydroisomerization of long-chain n-alkanes

Bifunctional catalysts with high isomerization activity and mono-branched isomer selectivity are urgently demanded for dewaxing long-chain n-alkanes. In particular, branching location of mono-branched isomer is difficult to control by current techniques. In this study, SSZ-32 zeolite with tunable distribution depth of acid sites in micropore channels is successfully prepared by ion exchange under partial template protection. Loaded with similar Pt nanoparticles, these SSZ-32 catalysts exhibit tunable activity and selectivity for hydroisomerization of n-hexadecane. Characterization results show that the adsorption model and insertion depth of n-alkane is altered by changing the distribution depth of acid sites in SSZ-32 micropore channels. When acid sites distribute in a moderate depth (∼ 4.5 nm) of the micropore channels, high yield of center-position mono-branched isomers (46.85%) is achieved, cracking reaction is significantly inhibited. The mole ratio of 6−/7−/8-methyl isomers to 2−/3-methyl isomers was increased to at least 1.3 times of the traditional catalyst with acid sites distributed throughout the micropores. The cold flow properties of lube base oils in isomerized dewaxing of Fischer-Tropsch wax are improved significantly by achieving an optimal and effective diffusion depth of reaction intermediates in the MTT micropore channels. Efficient and selective hydroisomerization of long-chain n-alkane is realized on Pt/SSZ-32 prepared by the facile partial-detemplation method.

Pt Single Atom-Anchored CeOx/SAPO-11 for Highly Efficient Hydroisomerization of n-Heptane

Single atomic catalysts (SAC) isolated in zeolite have been reported for hydroisomerization of n-alkanes. However, it is widely found that metal species located outside zeolite crystals have beneficial effects on catalytic performance, rather than inside zeolite. Herein, we introduce cerium oxide as a binder to anchor Pt single atoms on the catalyst surface. Pt species were atomically dispersed on catalyst surface certified by AC HAADF-STEM and XAS. Pt1@CeOx/SAPO-11 not only shows significant activity but also effectively inhibits the selectivity of cracking or hydrogenolysis. The turnover frequency value of 0.05%Pt1@CeOx/SAPO-11 reaches 9511 h−1, 13 times higher than reported catalyst prepared with the space-confined strategy. Reaction mechanisms have been proposed to explain the different effects of platinum status and location on the reaction. Platinum single atoms located outside the catalyst crystal are speculated more favourable to this reaction. Conceptually, catalytic efficiency of this reaction can be improved by dispersing the active sites to reduce the local concentration of the product of a reversible step in an intermediate reaction. An appropriate loading of 0.05 wt% is needed to achieve the high efficiency of the metal and acid sites simultaneously.

Superior activity and isomerization selectivity in n-dodecane hydroisomerization over Ni clusters on ZSM-22 zeolite with structural defects

Developing nonnoble catalysts with high performance for the selective hydroisomerization of long-chain n-alkanes to isoalkanes that are comparable to commercial Pt catalysts is important but challenging. We report a low-loading nickel catalyst on structure-defective nanosized ZSM-22 zeolite (Ni/SD-HZSM-22, 1.0 wt%) with superior activity and isomerization selectivity for n-dodecane hydroisomerization than a commercial Pt catalyst (Pt, 0.5 wt%). The developed Ni/SD-HZSM-22 catalyst achieves 86.0–88.6 % n-dodecane conversion and 80.0–81.3 % C12-isomer yield, outperforming the conventional ZSM-22–supported Ni catalyst (Ni/HZSM-22; 50.4 % and 41.1 %, respectively) and the commercial Pt catalyst (56.8 % and 52.4 %, respectively) under the same reaction conditions, with high durability for 120 h. This is because SD-HZSM-22 with abundant surface structural defects increased available 10-membered ring openings, anchoring the small-sized Ni species and enhancing the isomerization activity and selectivity, endowing Ni/SD-HZSM-22 with good synergy between metal and acid functions.

Investigating the hydroisomerization of n-pentane using Pt supported on ZSM-5, desilicated ZSM-5, and modified ZSM-5/MCM-41

The hydroisomerization of n-alkanes is a promising way to enhance the octane number of fuels over noble metal-promoted zeolites. Due to mass transfer limitations, zeolites with microporous structure and acidic properties suffer from lower selectivity to isomerized products. In this work, a series of hierarchical ZSM-5 and MCM-41/ZSM-5 composites are synthesized by desilication and desilication-reassembly methods to investigate the shape effect of pores on the Hydroisomerization of n-pentane. The physicochemical properties of the prepared samples were evaluated using XRD, XRF, N2 adsorption-desorption, FTIR, FE-SEM, HR-TEM, ICP-OES, and NH3-TPD. The catalytic performance of the prepared samples was carried out at atmospheric pressure in the temperature range of 200–400 °C. The ZSM-5/MCM-41 sample synthesized under a pH value of 8.5 showed a 10% and 15% higher yield of iso-Pentane and about 10%-20% higher conversion of n-pentane than the parent ZSM-5 and desilicated ZSM-5 respectively. These results demonstrated that a well-developed micro/mesoporous structure with a higher specific surface area (more than 400 m2/g) could provide better mass transfer properties and accessibility of active sites for reactant molecules. Also, a better balance between acidic and metallic sites and higher dispersion of Pt prevents further secondary cracking reactions and enhances the RON of the product stream.

A non-noble metal supported catalyst with potential prospect for hydroisomerization of n-hexadecane: Second metal incorporated NiMe/SAPO-11 catalyst with superior hydroisomerization performance

Aiming at the problems of high cost and high sensitivity to sulfur compounds in the raw materials of the noble metal supported hydroisomerization catalysts, this paper proposed preparing a series of bimetallic supported catalysts (NiMe/SAPO-11) with Ni as the main metal and non-noble metals (La, Ga, Ce and Zr) as the second metal additives for the hydroisomerization of n-hexadecane. A series of physicochemical characterization results showed that the introduction of the second metal additive reduced the acid amount and mesoporous volume of the bimetallic supported catalysts. However, the second metal additive weakened the interaction between the metal active phase and the supports, and promoted more Ni species to form hydrogenation/dehydrogenation active phases. The results of HRTEM and XPS show that the electrons in the d conduction band of the second metal additive can be transferred to the electron vacancy in the 3d conduction band of Ni, thus forming alloy compounds. The second metal additive played the role of “diluting” the Ni species, reducing the particle size of the metal active phase, thus greatly improving the catalytic performance of NiMe/SAPO-11. The catalytic performance of NiGa/SAPO-11 was the best, with a maximum yield of i-hexadecane of 64.90%, which is comparable to the maximum yield of i-hexadecane of 68.80% for the hydroisomerization of n-hexadecane catalyzed by Pt/SAPO-11. This is expected to provide a new strategy for the preparation of low-cost and efficient catalysts for the hydroisomerization of n-alkanes.

Modulating Acid Site Distribution in Mtt Channels for Controllable Hydroisomerization of Long-Chain N-Alkanes

Modulating Acid Site Distribution in Mtt Channels for Controllable Hydroisomerization of Long-Chain N-Alkanes

Influences of the metal-acid proximity of Pd-SAPO-31 bifunctional catalysts for n-hexadecane hydroisomerization

Hydroisomerization of n-alkanes over bifunctional catalysts is an effective approach for clean fuel production. However, it is still challenging to achieve metal-acid synergy and enhance the catalytic performance by preparation of bifunctional catalysts with suitable proximity between the metal sites and Brønsted acid sites. In this work, three series of bifunctional catalysts with different metal-acid proximities are prepared simply by mixing of SAPO-31 supported Pd (xPd/S) and γ-Al2O3 powders (xPd/S-A(C)), γ-Al2O3 supported Pd samples (xPd/A) and SAPO-31 powders (xPd/A-S(M)), and the mechanical mixing of shaped xPd/A and SAPO-31 granules (xPd/A-S(F)), respectively. The physico-chemical properties and the catalytic performance for the hydroisomerization of n-hexadecane have been investigated. Compared with the xPd/S-A(C) catalysts with the closest proximity between two active sites, the xPd/A-S(M) catalysts with moderate proximity at the micrometer scale demonstrate enhanced catalytic performance in the n-hexadecane hydroisomerization at temperatures above 340 °C. Inparticular, for the 0.15Pd/A-S(M) catalyst with a loading of 0.15 wt% Pd, the highest iso‐hexadecane yield of 80.4% was obtained at the n-hexadecane conversion of 90.4%. Therefore, this work provides an effective route for the simple preparation of bifunctional catalysts with lower Pd loading and favorable metal-acid balance for highly selective hydroisomerization of long-chain n-alkanes.