Hydroisomerization Of N-dodecane Research Articles

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.

Ni catalyst on ZSM-22 nanofibers bundles with good catalytic performance in the hydroisomerization of n-dodecane

Developing non-noble catalyst with high performance is significant in the hydroisomerization of long-chain n-alkane to iso-alkanes. In this study, nanofiber-bundled ZSM-22 without any additives was successfully synthesized and used to prepare Ni catalyst (Ni/NB-HZSM-22, Ni loading 1.0 wt%) for hydroisomerization of n-dodecane (n-C12). The obtained Ni/NB-HZSM-22 catalyst exhibited much higher intrinsic catalytic activity (TOF = 0.077 s−1) than a conventional needle-shaped ZSM-22 supported Ni catalyst (Ni/C-HZSM-22, 0.026 s−1), especially higher isomerization selectivity (TOFiso, 0.071 s−1) than the Ni/C-HZSM-22 catalyst (0.021 s−1). Additionally, the Ni/NB-HZSM-22 catalyst had lower cracking/iso-dodecanes (iso-C12, 0.08) and di-branched/mono-branched (0) ratios than the Ni/C-HZSM-22 catalyst (0.25 and 0.07) after extrapolation of the n-C12 conversion to zero. This is mainly attributed to the nanofiber–bundled NB-HZSM-22 with well-crystallized structures and suitable acidity, leading to good synergistic catalysis between metal and acidic function for the Ni/NB-HZSM-22 catalyst. Although the Ni catalyst on the parent NB-ZSM-22 was less active, it had a similar optimal iso-C12 yield compared to the Ni/NB-HZSM-22 catalyst. In addition, the Ni/NB-HZSM-22 catalyst showed a maximum iso-C12 yield of 74.8%, which was much better than the Ni/C-HZSM-22 catalyst (58.7%), and showed comparable performance to a Pt catalyst on the NB-HZSM-22 (76.7%). These results suggested that the Ni catalyst on the NB-HZSM-22 was a promising candidate for the hydroisomerization catalyst.

Conquering the solubility barrier of di-n-octylamine as structure-directing agent in hierarchical silicoaluminophosphate synthesis by using phase-transfer synthesis

Silicoaluminophosphates (SAPOs) are a class of microporous solids employed as solid acid catalysts or adsorbents in petrochemical and coal chemical processes, which are often generated in hydrothermal synthesis using water-soluble organic structure-directing agents (OSDA), resulting in the formation of micron sized, rod-like crystals running along pore-channel direction for unidimensional SAPOs. The use of a low-cost, barely soluble di-n-octylamine (DOA) as OSDA in a water/toluene biphasic media to crystallize SAPO-31 is reported. The product is disclosed to be a hierarchically porous material built up of self-assembled nanocrystals (∼110 nm) with enhanced diffusion property and preserved acidity comparable to that of a standard sample derived using di-n-hexylamine as OSDA. The formation is mediated by the formation of a Pickering emulsion structure that favors crystal nucleation over growth, thus overcoming the solubility barrier of candidate OSDA. The obtained material exhibited higher isomer yield in catalytic hydroisomerization of n-dodecane compared to the control sample. Product distribution analysis discloses that mono-branched isomers are generated mainly inside the micropores, while di-branched isomers are produced via key-lock catalysis on pore-mouth sites. The increase in isomerization selectivity is attributed to the formation of more mono-branched isomers and their lowered cracking probability associated with enhanced diffusion property. This new synthetic protocol expands the toolkit of candidate OSDAs towards hydrophobic molecules and exemplifies porogen-free fabrication of hierarchical SAPOs. The uncovered origin of shape-selectivity offers a guidance towards manipulating hydroisomerization product slates.

Hydro-isomerization of n-dodecane on Pt–La/Beta catalyst for the production of high quality bio-jet fuel: Effect of La addition

A series of Pt–La/B38 catalysts were prepared for low-temperature isomerization of n-dodecane and the effects of La addition on the textural properties, metal dispersion, acid properties, and catalytic performance were investigated. La co-impregnated with Pt on B38 significantly reduced the Pt size and notably enhanced the uniformity in Pt size. A higher ratio of accessible Pt and medium-strength Brønsted acid sites and a shorter distance between two Pt particles of Pt–La10/B38 resulted in the maximum iso-C12 yield (59.2–56.2%) in the range of 200–250 °C, due to the reasonable arrangement of active sites caused by La loading.

Preparation of ZSM-22/ASA composite material for enhancing n-dodecane hydroisomerization performance

The ZSM-22/ASA composite material for efficient hydroisomerization of n-dodecane was successfully prepared via a two-step synthesis method. The structure, pore properties, and acidity of the catalysts were elucidated by the means of XRD, N2 physical adsorption, TEM, FT-IR, and Py-IR. Compared with the mixture catalyst, ZSM-22/ASA has a higher average pore diameter and formed a uniform and open channel structure, which is favorable to the diffusion of the reactant and the efficiency of the acid sites. The zeolite and the ASA phase in the composite are closely bonded by the interface effect, forming an additional Si–O–Al structure, which significantly affected the acidity of the composite catalyst. ZSM-22/ASA composite material exhibits enhanced n-dodecane hydroisomerization selectivity of total isomers and multi-branched isomers, which is attributed to its proper acid strength and pore structure conducive to diffusion. Finally, the location distribution of branched methyl groups was discussed and enhanced more central branching iso-dodecanes was obtained over the ZSM-22/ASA composite material.

Influence of nickel loading on the hydroisomerization of n-dodecane with nickel-tungsten oxide-alumina supported catalysts

Heterogeneous catalysts based on alumina-supported tungsten oxides (15 wt% W) with different loadings of nickel (0.5, 1, 2, 4, 6, 8 and 10 wt% Ni) were selected to study the influence of Ni loading on the hydroisomerization of n-dodecane. The catalysts were prepared by applying the wetness impregnation method on the supports to introduce W and Ni. The characterization techniques applied for determining physicochemical properties of the catalysts were N2 adsorption-desorption at 77 K (textural properties), X-ray diffraction (structure and crystalline phases), H2-TPR (redox properties), FTIR, NH3-TPD (acid sites analyses) and XPS (chemical surface analysis). The catalytic properties of such catalysts were found to be crucial in the n-dodecane conversion. The NH3-TPD profiles indicate that the medium acid sites are the main sites responsible for the reaction performance. The formation of bulky crystal structures of nickel species in the high nickel loading catalyst (10 wt% Ni) was confirmed by XRD and XPS results, resulting in the largest cracking activity. The conversion of n-dodecane and selectivity to i-C12+branched C12 tend to increase with Ni loading until the catalyst contains 6 wt% Ni (28% n-C12 conversion and 94% of branched C12 selectivity). The lower selectivity at high nickel loading is due to metal-based cracking reaction. An optimum balance between metal and acid centers is needed to achieve a compromise between conversion and selectivity, avoiding or minimizing cracking reactions.

Influence of W loading, support type, and preparation method on the performance of zirconia or alumina-supported Pt catalysts for n-dodecane hydroisomerization

Catalysts based on zirconia and alumina-supported tungsten oxides (3–18 wt% W) with a small loading of platinum (0.3 wt% Pt) were selected to study the influence of W loading, support type, and preparation methods on the hydroisomerization of n-dodecane. The alumina- and zirconia-supported catalysts show different catalytic properties that play an important role in n-dodecane conversion. Specific surface area and acidity of the alumina-supported catalysts are clearly higher than those of zirconia-supported counterparts. The 15 wt% W loaded catalysts were found to exhibit the best catalytic performance for the hydroisomerization of n-dodecane for both zirconia and alumina (67% of n-C12 conversion and 87% of i-C12 selectivity) based catalysts. Catalysts prepared by a single-step wet impregnation method were more active in the hydroisomerization of n-dodecane than catalysts prepared via several consecutive steps.

Ni Catalyst on Zsm-22 Nanofibers Bundles with Good Catalytic Performance in the Hydroisomerization of N-Dodecane

Ni Catalyst on Zsm-22 Nanofibers Bundles with Good Catalytic Performance in the Hydroisomerization of N-Dodecane

Hydro-Isomerization of N-Dodecane on Pt-La/Beta Catalyst for the Production of High Quality Bio-Jet Fuel: Effect of La Addition

Hydro-Isomerization of N-Dodecane on Pt-La/Beta Catalyst for the Production of High Quality Bio-Jet Fuel: Effect of La Addition

Influence of the Reduction Temperature and the Nature of the Support on the Performance of Zirconia and Alumina-Supported Pt Catalysts for n-Dodecane Hydroisomerization

Catalysts based on zirconia- and alumina-supported tungsten oxides (15 wt % W) with a small loading of platinum (0.3 wt % Pt) were selected to study the influence of the reduction temperature and the nature of the support on the hydroisomerization of n-dodecane. The reduction temperature has a major influence on metal dispersion, which impacts the catalytic activity. In addition, alumina and zirconia supports show different catalytic properties (mainly acid site strength and surface area), which play an important role in the conversion. The NH3-TPD profiles indicate that the acidity in alumina-based catalysts is clearly higher than that in their zirconia counterparts; this acidity can be attributed to a stronger interaction of the WOx species with alumina. The PtW/Al catalyst was found to exhibit the best catalytic performance for the hydroisomerization of n-dodecane based on its higher acidity, which was ascribed to its larger surface area relative to that of its zirconia counterparts. The selectivity for different hydrocarbons (C7–10, C11 and i-C12) was very similar for all the catalysts studied, with branched C12 hydrocarbons being the main products obtained (~80%). The temperature of 350 °C was clearly the best reduction temperature for all the catalysts studied in a trickled-bed-mode reactor.

Design and synthesis of Pt catalyst supported on ZSM-22 nanocrystals with increased accessible 10-MR pore mouths and acidic sites for long-chain n-alkane hydroisomerization

Abstract Synthesis of ZSM-22 with more accessible 10-membered ring (10-MR) openings is important for the preparation of highly active and selective hydroisomerization catalyst. Herein, we synthesized ZSM-22 nanocrystals (HZSM-22-NA) with more 10-MR openings and a mesoporous structure on a large scale. The prepared Pt/HZSM-22-NA catalyst (4.74 × 10−6 mol·g−1·s−1) exhibited higher intrinsic activity than conventional HZSM-22-supported Pt catalyst (Pt/HZSM-22, 2.65 × 10-6 mol·g−1·s−1) in the hydroisomerization of n-dodecane. Additionally, Pt/HZSM-22-NA had higher C12 isomer selectivity (93.5%) and lower cracking selectivity (6.5%) than Pt/HZSM-22 (79.8% and 20.2%) at the same n-dodecane conversion level (~90%). These features could be due to the change in the porous structure and acidity between HZSM-22-NA and HZSM-22. HZSM-22-NA composed of nanocrystals at c-axis could double the number of accessible 10-MR openings and acidic sites, thus enhancing the isomerization activity of Pt/HZSM-22-NA. Furthermore, the mesoporosity of HZSM-22-NA facilitated mass transfer of the intermediates and products, thus inhibiting cracking reaction.

Melting-assisted solvent-free synthesis of SAPO-11 for improving the hydroisomerization performance of n-dodecane

A novel melting-assisted solvent-free route using solid oxalic acid was proposed for the post-treatment of SAPO-11 zeolite, followed by loading with 0.5 wt% Pt by the incipient wetness impregnation method. Subsequently, the performance of the obtained bifunctional catalysts toward the hydroisomerization of n-dodecane was examined. The prepared samples were characterized by XRD, SEM, BET, XRF, Py-IR, and solid-state NMR. From the results, it was found that the high crystallinity and uniform morphology were retained after the post-treatment and that more (002) crystal faces were exposed, which was beneficial since more acid sites were provided. More importantly, the total Brönsted acid sites and the ratio (Ra) of the micropore area to the total surface area were optimized by this method. Thus, the catalytic performance was enhanced significantly, and the prepared Pt-SAPO-11-10% catalyst had the highest i-dodecane yield of 80.1% compared to 55.3% of Pt–SAPO-11. Expectedly, this facile and cost-effective method is promising for the hydroisomerization of normal paraffin in the production of lubricant base oils.

N-dodecane hydroisomerization over Pt/ZSM-22: Controllable microporous Brönsted acidity distribution and shape-selectivity

The controllable acidity distribution in micropore for ZSM-22 zeolites is successfully tailored by using a new template protective NH4+ exchange strategy. The location and density of microporous Brönsted acidity is tailored by controlling the degree of detemplation and the concentration of NH4+ aqueous solution, respectively. The distribution of microporous Brönsted acidity of these Pt/ZSM-22 catalysts obviously affects the shape-selectivity in the hydroisomerization of n-dodecane. Weak microporous acidity leads to the formation of centrally mono-branched isomers, while strong microporous Brönsted acidity near the pore mouth favors the formation of multi-branched isomers, and strong microporous Brönsted acidity deep inside the pore mouth favors cracking through (s, p) β-scission. By selectively tailoring microporous Brönsted acidity near the pore mouth with lower acid density, the isomer yield over Pt/ZSM-22 was increased from 40.7% to 63.7%. This enhanced catalytic performance comes from the preferable formation of centrally mono-branched isomers and multi-branched isomers through key-lock model.

Effect of Metal Precursors on the Performance of Pt/SAPO-11 Catalysts for n-Dodecane Hydroisomerization.

Pt(NH3)4(NO3)2, Pt(NH3)4(Ac)2, (NH4)2PtCl4, and H2PtCl6 were used to prepare Pt/SAPO-11 catalysts to investigate the effect of Pt precursors on the hydroisomerization of n-dodecane. The catalyst derived from Pt(NH3)4(NO3)2 displays the best hydroisomerization activity and selectivity among these precursors. The hydroisomerization conversion of n-dodecane is affected by the platinum particle size, platinum dispersion, the location of platinum, and the valence state of platinum. The selectivity of n-dodecane is determined by the number of Brønsted acid sites and Pt crystal planes. These conclusions are verified by combining transmission electron microscopy, high-resolution transmission electron microscopy, hydrogen temperature programmed reduction, NH3-temperature programmed desorption, and Py-IR studies. The catalyst prepared with Pt(NH3)4(NO3)2 as the precursor exhibits the smallest platinum particle size and the highest platinum dispersion. Most of the platinum particles are supported on the external surface of SAPO-11 with the Pt(111) crystal face. Such a catalyst also possesses a suitable number of Brønsted acid sites and then displays the best catalytic performance. Obviously, the use of various precursors for the Pt-based catalyst can significantly affect the performance of Pt/SAPO-11 for the hydroisomerization of n-dodecane.

Synthesis of Fe-ZSM-23 zeolite and its catalytic performance for the isomerization of n-dodecane

The introduction of transition metal atoms into zeolites can significantly improve their catalytic performance. Herein, a series of Al free Fe-ZSM-23 zeolites were synthesized via hydrothermal synthesis. The samples were characterized by XRD, SEM, N2-physical adsorption, UV/Vis, FTIR, XPS, ICP, NH3-TPD and Py-IR. In addition, the hydroisomerization of n-dodecane were conducted over the zeolites loading 0.5 wt% Pt. The effect of Fe in the zeolites on catalyst acidity and alkane isomerization was studied. The results showed that the introduction of Fe in the zeolite framework can increase the isomerization selectivity, while an extremely low Fe content resulted in a significant decrease in catalyst activity and isomerization selectivity.

Design of fast crystallization of nanosized zeolite omega crystals at higher temperatures

Fast crystallization of nanosized zeolite crystals is a very popular process used for practical zeolite catalyst applications. Herein, we report a designer crystallization process for nanosized zeolite omega crystals based on the relationship between the crystallization time and temperature in the Arrhenius equation. Compared to the conventional hydrothermal synthesis of zeolite omega (72 h at room temperature and 240 h at 100 °C, MAZ-100), the crystallization of zeolite omega presented in this work only requires a very short time interval (5 h at 180 °C, MAZ-180). Physicochemical characterizations, including XRD, SEM, N2 sorption isotherms, and 27Al MAS NMR show that the product of zeolite omega (MAZ-180) has good crystallinity and uniform nanocrystals. More importantly, after the loading of Pt nanoparticles (0.5 wt%), the Pt/H-MAZ-180 catalyst exhibits higher isomer selectivity and lower cracking selectivity than those of the Pt/H-MAZ-100 catalyst in the hydroisomerization of n-dodecane. These results suggest the potential applications of these omega nanocrystals as supporting catalyst compounds in industrial processes.

Hydroisomerization of n-dodecane over bi-porous Pt-containing bifunctional catalysts: Effects of alkene intermediates’ journey distances within the zeolite micropores

In this study, three micro/mesoporous composites with MCM-41 materials overgrowing on external surfaces of Y zeolite crystals were prepared. For the three composites, average crystal particle sizes of their zeolite components differed from each other, resulting from the different levels of alkali-treatments to the original Y zeolite before the composite synthesis. Hydroisomerization of n-dodecane (n-C12) was used to evaluate the catalytic performances of bi-porous Pt-loaded composite catalysts with similar metal-acid balances but different average zeolite crystal particle sizes, which leaded to the distinction of alkene intermediates’ journey distances inside the acid-rich micropores between two accessible Pt metal sites on three catalysts. The number of protonic sites encountered by alkene intermediates along their diffusion paths, determining the skeletal transformation frequencies, was considered to be proportional to the above-mentioned intermediates’ journey distances. Results showed that bifunctional catalysts with smaller average zeolite crystal particle sizes outperformed the catalyst containing the original Y zeolite in the regard of isomerization selectivity. This implied the significant effect of intermediates’ journey distances within the microporous arrays between two Pt sites on bifunctional behaviors of catalysts. It can be confirmed that shortening this distance within certain limits indeed contributed to inhibiting secondary reactions, including the skeletal multiple branching and cracking.

Preparation and Performance of Pt/IZM-2 Catalyst on the Hydroisomerization of n-Dodecane†

Preparation and Performance of Pt/IZM-2 Catalyst on the Hydroisomerization of n-Dodecane†

Confined-space synthesis of hierarchical MgAPO-11 molecular sieves with good hydroisomerization performance

Hierarchical MgAPO-11 molecular sieves with large BET surface areas and high pore volumes have been synthesized via dry-gel conversion of the magnesioaluminophosphate-carbon (MAP-C) composites. The carbon film coated on the mesopores of amorphous magnesioaluminophosphate (MAP) provides a confined-space to restrict the overgrowth of the crystals. The products were well characterized using XRD, SEM, TEM, N2 adsorption-desorption, infrared spectroscopy of pyridine adsorption (Py-IR) and solid-state NMR techniques. The results show that highly mesoporous MgAPO-11 with good crystallinity can be obtained at an appropriate carbon loading amount. The time-dependent study indicates that the formation process of hierarchical MgAPO-11 obeys a reversed crystal growth route: crystallization started on the outer surface of the amorphous precursor, then extended to inward, and finally hierarchical molecular sieves assembled by nanosized crystals with a size of about 50 nm were obtained. The catalyst based on hierarchical MgAPO-11 exhibits a significant higher activity and selectivity than the conventional Pt/MgAPO-11 catalyst in the hydroisomerization of n-dodecane, attributing to its higher acidity and excellent diffusion properties resulting from the hierarchical pore architecture.

Highly mesoporous SAPO-11 molecular sieves with tunable acidity: facile synthesis, formation mechanism and catalytic performance in hydroisomerization of n-dodecane

Hierarchical SAPO-11 molecular sieves with tunable acidity fabricated by a facile dry-gel conversion approach show excellent performance in hydroisomerization of n-dodecane.