High Isomerization Selectivity Research Articles

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.

Effects of Zr, Al, and mordenite on Pt-MCM-48 catalyst in n-heptane isomerization: preparation, characterization and catalytic performance

Herein, platinum-loaded MCM-48-Mordenite, Al-MCM-48, Al-MCM-48-Mordenite, Zr-MCM-48, and Zr-MCM-48-Mordenite catalysts were synthesized and studied for the isomerization reaction of n-heptane at four different temperatures. XRD, XRF, FT-IR, UV-Vis DRS, NH3-TPD, TG/DTA and BET analysis were used to characterize the structural characterizationand acid distribution of these catalysts. The Pt/Mordenite catalyst showed higher hydrogenation and cracking activity, while the hybrid catalysts showed better isomerization selectivity. The Pt/Al-MCM-48-Mordenite catalyst showed the best catalytic behavior at 200 °C with a suitable n-heptane conversion (78.8%) and the highest isomer selectivity (81.9%). The maximum isomerization selectivity as well as the maximum yield of multi-branched isomers are probably not only due to the suitable acidity and the large pores, but also to the higher metal dispersion. This result shows that the Pt/Al-MCM-48-Mordenite catalyst can be a hopeful candidate for good n-heptane isomerization catalysts.

Synthesis and hydrogen isomerization performance of ordered mesoporous nanosheet SAPO-11 molecular sieves

In this study, ordered mesoporous nanosheet SAPO-11 molecular sieves were synthesized using uncalcined SBA-15 molecular sieves as a Si source. The effects of different Si sources on the structure and properties of SAPO-11 molecular sieves were examined, and their growth mechanism was elucidated. An electrostatically polarized region was formed between a P123 template (triblock copolymer) contained in uncalcined SBA-15 and two-dimensional channels of SBA-15 molecular sieves. When AlO2− and PO2+ species diffused into this region, its electrostatic polarization promoted the preferential growth of SAPO-11 molecular sieves along the c-axis, which contained a large number of exposed catalytically active sites with acidic properties. During the isomerization of long-chain alkanes, the synthesized sieves exhibited high isomerization activity and selectivity. When the conversion rate of n-dodecane reached 87.96%, the yield of i-dodecane was 68.08%, and the yield of multi-branched i-dodecane was 31.65%.

Modification of commercial Y zeolites by alkaline-treatment for improved performance in the isomerization of glucose to fructose

• Alkaline-treatment of H-Y resulted in mesopores and tetrahedral extra-framework lewis acidic al. • Alkaline-treated H-Y yielded high isomerization selectivity and low side product formation. • Na-Y unaffected by alkaline-treatment maintaining low isomerization performance despite a high number of acidic sites. Isomerization of glucose to fructose is a key reaction step in the efficient production of valuable renewable chemical intermediates from biomass. Zeolites have been widely used to promote glucose isomerization, but only limited structure-activity relationship has been established and applied to optimize the reaction. In this work, commercial Y zeolites were modified by alkaline-treatment and their physicochemical properties and structures were correlated in order to optimize the catalytic performance for glucose isomerization. For H-Y, the alkaline-treatment developed new mesoporous structures with larger pore, modified the Si-O(H)-Al bonds and extracted silica from framework structures creating more tetrahedral extra-framework Lewis acidic aluminum. This increased the isomerization selectivity towards fructose more than twelve times and decreased significantly acetalization/ketalization side reactions compared to the pristine zeolite. In contrast, Na-Y contained mainly micropores and had less tetrahedral non-framework acidic Al-species, resulting in low glucose conversion and low fructose yield due to limited substrate accessibility to the pores, although the number of acid sites was tenfold higher than in H-Y. The study demonstrates how commercial Y zeolites can be designed by alkaline-treatment to comprise mesopores and weak acid sites, which greatly improve the catalytic performance for glucose isomerization to fructose.

Fabrication of sea urchin-like hierarchical porous SAPO-11 molecular sieves toward hydrogenation of lipid to jet fuel

Novel sea urchin-like hierarchical porous SAPO-11 molecular sieves were fabricated by adding CTAB after pre-crystallization. High isomer selectivity (78.2%) was observed for the sea urchin-like SAPO-11 loaded with Ni.

Synthesis of Ni-Modified ZSM-5 Zeolites and Their Catalytic Performance in n-Octane Hydroconversion.

Ni-modified ZSM-5 zeolites with different nickel contents were successfully prepared by the in situ synthesis method and the impregnation method. The synthesized samples were characterized by XRD, SEM, N2 adsorption–desorption isothermals, and Py-FTIR. The characterization results show that both the textural properties and crystallization of Ni-modified ZSM-5 zeolites were preserved well, and their acidic properties can be modulated after nickel modification. The corresponding NiMo catalysts supported on Ni-modified ZSM-5 zeolites were prepared by the incipient wetness co-impregnation method, and their catalytic performances were evaluated in n-octane hydroconversion. Compared to the those modified by the in situ synthesis method, ZSM-5 zeolite-supported catalysts modified by the impregnation method exhibit higher stability and higher isomerization selectivity. This is due to the synergistic effect between Brønsted acid sites and Lewis acid sites on the Ni-modified ZSM-5 zeolites, especially for the NiMo/1Ni-Z5 catalyst.

Investigation on n-Alkane Hydroisomerization, a Comparison of IM-5 to ZSM-5 Zeolites

Porosity and acidity of zeolites are key factors for highly efficient catalyst design. Herein, we investigate the isomerization performance of a high-silica zeolite IM-5 which has a unique limited 2.5 nm “nanoslab” pore structure. Compared with the reference ZSM-5, the higher adsorption amount and rate of IM-5, proven by adsorption experiments of n-heptane and toluene, resulted in a higher isomer selectivity in n-C7 or n-C16 hydroisomerization reactions, which increased relatively by 19.5% and 91.5%, respectively. Furthermore, IM-5 also shows higher n-C7 or n-C16 conversion due to its more strong acid sites. Additionally, mesopore introduction into IM-5 significantly increases isomer selectivity, especially for long chain n-C16. The selectivities of C7 isomers and C16 isomers of mesoporous M-IM-5 increase relatively by 73.3% and 216.1% compared with microporous IM-5. Mesopores and reduced diffusion length facilitate the mass transport of bulky molecules, then decrease subsequent cracking side reaction tha...

Skeletal isomerization of n-heptane with highly selective Pt/H3PW12O40/SBA–15 trifunctional catalysts

For the first time, highly selective Pt/H3PW12O40/SBA–15 trifunctional catalysts were evaluated for n-heptane hydroisomerization. Both Lewis (L) and Brønsted (B) acid sites were present in these catalysts. Reduction treatment led to heteropolyacid dispersion better and Pt nanoparticles smaller. With the best 1wt%Pt/20wt%H3PW12O40/SBA–15 catalyst, 100% isomerization selectivity and 56.74% n-heptane conversion were obtained at 320°C. Among the products, the dibranched isomers concentration faction was >50% and 2,2-dimethylpentane was predominant. Pt/H3PW12O40/SBA–15 catalysts with Pt nanocrystals, proper acidity strength and a balanced ratio of B/L acid sites, and highly ordered large mesopores were chiefly responsible for the high isomerization selectivity.

Computational Screening of Nanoporous Materials for Hexane and Heptane Isomer Separation

Computational high-throughput screening was carried out to assess a large number of experimentally reported metal–organic frameworks (MOFs) and zeolites for their utility in hexane isomer separation. Through the work, we identified many MOFs and zeolites with high selectivity (SL+M > 10) for the group of n-hexane, 2-methylpentane, and 3-methylpentane (linear and monobranched isomers) versus 2,2-dimethylbutane and 2,3-dimethylbutane (dibranched isomers). This group of selective sorbents includes VICDOC (Fe2(BDP)3), a MOF with triangular pores that is known to exhibit high isomer selectivity and capacity. For three of these structures, the adsorption isotherms for a 10-component mixture of hexane and heptane isomers were calculated. Subsequent simulations of column breakthrough curves showed that the DEYVUA MOF exhibits a longer process cycle time than VICDOC MOF or MRE zeolite, which are previously reported, high-performing materials, illustrating the importance of capacity in designing MOFs for practical ...

Gallium Modified HUSY Zeolite as an Effective Co-support for NiMo Hydrodesulfurization Catalyst and the Catalyst's High Isomerization Selectivity.

The effects of metal-modified acidic co-supports on the hydrodesulfurization (HDS) activity and isomerization selectivity of highly refractory organosulfur compounds such as 4,6-dimethyldibenzothiophene have been investigated. Y zeolite crystals with high Si/Al ratios and small crystallite sizes were successfully synthesized by a new hydrothermal synthesis approach. The synthesized Y zeolite crystals were ion-exchanged and stabilized. The prepared samples were then modified with different gallium contents using an impregnation method to adjust their acidity properties, and these modified samples were used as co-supports for NiMo sulfide HDS catalysts. The catalyst containing 10 wt.% zeolite Y modified by 2 wt.% gallium (NiMo/2GaY-ASA-A) exhibited the highest HDS activity, with 4,6-dimethyldibenzothiophene (4,6-DMDBT) conversion nearly double the rate of the catalyst without zeolite at 563 K, 4.0 MPa and liquid hourly space velocity (LHSV) of 40 h-1 . NiMo/2GaY-ASA-A also exhibited superior isomerization ability, with 3,4'-DMBP, 4,4'DMBP, and 3,6-DMDBT as the main products, indicating that the isomerization pathway was the main reaction route over NiMo/2GaY-ASA-A. The superior catalytic performance is related to the synergistic effect of the proper amount of medium and strong Brønsted acid sites. The compounds 3,6-DMDBT and 3,7-DMDBT (isomers of 4,6-DMDBT) and 3,4,6-TMDBT and tetra-methyl-DBT (transmethyl products) were detected simultaneously in the HDS product of 4,6-DMDBT for the first time over NiMo/GaY-ASA-A catalysts. Finally, a new reaction network over NiMo/2GaY-ASA-A was proposed.

Single isomerization selectivity of glucose in methanol over Sn-BEC zeolite of homogenous Sn distribution

Sn-zeolites are important solid Lewis acid catalysts with wide applications to the conversions of various biomass-derived carbohydrates. As the catalytic center, framework Sn of Sn-zeolites can catalyze glucose isomerization to fructose and epimerization to mannose. In practical use, the main obstacle to the application of Sn-zeolites is the lengthy crystallization. In present work, we developed a rapid synthesis route to Sn-zeolites by incorporating Sn into the germanosilicate framework of BEC zeolite via direct hydrothermal procedure. The synthesis time required by Sn-BEC is tenfold shortened than that by the traditional Sn-zeolites like Sn-Beta. The locations of framework Sn atoms of Sn-BEC were investigated by 19F MAS NMR and computational modeling, which indicates that the framework Sn sites of Sn-BEC adopt a uniquely homogenous distribution at the T1 sites. Sn-BEC exhibits high reaction activity and single isomerization selectivity in the glucose conversion in methanol, while Sn-Beta shows both isomerization and epimerization selectivity. The single isomerization selectivity of Sn-BEC suggests the presence of single catalytic center, which is probably caused by the homogenous distribution of framework Sn sites.

High selectivity for n-dodecane hydroisomerization over highly siliceous ZSM-22 with low Pt loading

Pt/siliceous ZSM-22 with silanol nests exhibits high isomer selectivity with low Pt loading.

Determining the Strength of Brønsted Acid Sites for Hydrodewaxing over Shape-Selective Catalysts

This paper reports a method for directly determining the effective strength of those acid sites on a molecular sieve catalyst that are actually involved in reactions such as hydrodewaxing. The method is here applied to the conversion of a waxy paraffin over a catalyst containing platinum and a SAPO-11 sieve of high isomerization selectivity, as well as a catalyst containing platinum and a H-ZSM-5 zeolite (SiO2/Al2O3 = 150) of high cracking selectivity. Results are compared against the measured Bronsted acid site strength on these molecular sieves determined from temperature-programmed desorption of ammonia and Fourier transform infrared analysis of adsorbed pyridine. Characterization of acid sites showed both concentration and apparent acid strength for H-ZSM-5 higher than those for SAPO-11, with the latter having a finite but smaller amount of strong acid sites that adsorbed pyridine at 573 and 673 K. Reactions with n-hexadecane gave significantly higher conversion rates on H-ZSM-5, and it is shown that ...

Synthesis, characterization and isomerization performance of micro/mesoporous materials based on H-ZSM-22 zeolite

Micro/mesoporous materials with different mesoporosities were prepared through recrystallization of H-ZSM-22 zeolite in alkaline solution with cetyltrimethylammonium bromide template (CTAB). The structure, morphology, pore properties, acidity and isomerization performance of the catalysts by using the resulting materials were characterized and assessed. The dissolution and recrystallization procedure introduced the well-developed mesoporous structure of MCM-41 type with the meso-scale channels of about 3nm in size on the outer surfaces of the microporous H-ZSM-22 zeolites, forming the micro/mesoporous materials, which possessed increased weak B acid sites at the pore mouths and a reduced amount of total acid sites. It is shown that the presence of well-developed mesopores could remarkably improve the selectivity to multi-branched products and suppress the side cracking reactions in n-dodecane isomerization. The micro/mesoporous Pt/ZSM-22/MCM-41 bifunctional catalyst with suitable recrystallization degree exhibits high isomerization selectivity under high conversion in long-chain n-alkane isomerization compared to the original microporous Pt/H-ZSM-22 catalyst.

Effect of reduction temperature of NiMoO3-x/SAPO-11 on its catalytic activity in hydrodeoxygenation of methyl laurate

To develop a non-sulfide and non-noble metal catalyst for the one step deoxygenation and isomerization of methyl laurate to hydrocarbons that are identical to diesel fuel, a SAPO-11 supported reduced nickel and molybdenum catalyst was prepared, and its performance was investigated after reduction pretreatment at various temperatures (400–550°C). For comparison, sulfided NiMo/SAPO-11, reduced NiO/SAPO-11 and MoO3/SAPO-11 were also studied. The reduction temperature exerted a significant influence on the deoxygenation activity, isomerization selectivity and deoxygenation pathway. The NiMo3-x/SAPO-11 catalyst that was reduced at a lower temperature (400°C) exhibited low deoxygenation activity but the highest isomerization selectivity. However, the activity subsequently increased over the catalyst reduced at 450°C, and was higher than that of the sulfided catalyst. In addition, the isomerization selectivity decreased with increasing reduction temperature. The high activity and isomerization selectivity are ascribed to the increase in the density of surface species of Mo4+ and Mo5+, respectively. With regard to the deoxygenation pathway, the catalyst reduced at 400°C exhibited a high decarbonylation selectivity that was similar to the nickel-catalyzed reaction. In contrast, the synergetic effect of the nickel metal and Mo4+ species can be responsible for the high selectivity toward hydrodeoxygenation over the catalyst reduced at higher temperatures (450–550°C).

Synthesis of NiMo hydrodesulfurization catalyst supported on a composite of nano-sized ZSM-5 zeolite enwrapped with mesoporous KIT-6 material and its high isomerization selectivity

A novel composite material ZSM-5/KIT-6 (ZK-W) was synthesized by enwrapping nano-sized ZSM-5 zeolite crystals with mesoporous KIT-6 silica. This composite was used as catalyst support for NiMo sulfide in the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The NiMo/ZK-W catalyst showed the highest HDS activity and its 4,6-DMDBT conversion was about double that of a conventional NiMo/Al2O3 catalyst at 320°C, 4.0MPa, and LHSV of 150h−1 and on the basis of sulfur. The superior catalytic performance of NiMo/ZK-W is related to the synergistic effect of the excellent diffusion through the hierarchical porous structure and the suitable Brønsted acid sites. 3,6-DMDBT and 3,7-DMDBT, two isomers of 4,6-DMDBT, were identified simultaneously for the first time in the HDS products of 4,6-DMDBT over the NiMo/ZK-W catalyst. The NiMo/ZK-W catalyst exhibited a superior isomerization ability, and 4,4′-dimethylbiphenyl was the main product, indicating that the isomerization pathway is the main reaction route. A new reaction network of 4,6-DMDBT HDS over NiMo/ZK-W catalyst was proposed.

High-temperature catalytic reforming of n-hexane over supported and core-shell Pt nanoparticle catalysts: role of oxide-metal interface and thermal stability.

Designing catalysts with high thermal stability and resistance to deactivation while simultaneously maintaining their catalytic activity and selectivity is of key importance in high-temperature reforming reactions. We prepared Pt nanoparticle catalysts supported on either mesoporous SiO2 or TiO2. Sandwich-type Pt core@shell catalysts (SiO2@Pt@SiO2 and SiO2@Pt@TiO2) were also synthesized from Pt nanoparticles deposited on SiO2 spheres, which were encapsulated by either mesoporous SiO2 or TiO2 shells. n-Hexane reforming was carried out over these four catalysts at 240-500 °C with a hexane/H2 ratio of 1:5 to investigate thermal stability and the role of the support. For the production of high-octane gasoline, branched C6 isomers are more highly desired than other cyclic, aromatic, and cracking products. Over Pt/TiO2 catalyst, production of 2-methylpentane and 3-methylpentane via isomerization was increased selectively up to 420 °C by charge transfer at Pt-TiO2 interfaces, as compared to Pt/SiO2. When thermal stability was compared between supported catalysts and sandwich-type core@shell catalysts, the Pt/SiO2 catalyst suffered sintering above 400 °C, whereas the SiO2@Pt@SiO2 catalyst preserved the Pt nanoparticle size and shape up to 500 °C. The SiO2@Pt@TiO2 catalyst led to Pt nanoparticle sintering due to incomplete protection of the TiO2 shells during the reaction at 500 °C. Interestingly, over the Pt/TiO2 catalyst, the average size of Pt nanoparticles was maintained even after 500 °C without sintering. In situ ambient pressure X-ray photoelectron spectroscopy demonstrated that the Pt/TiO2 catalyst did not exhibit TiO2 overgrowth on the Pt surface or deactivation by Pt sintering up to 600 °C. The extraordinarily high stability of the Pt/TiO2 catalyst promoted high reaction rates (2.0 μmol · g(-1) · s(-1)), which was 8 times greater than other catalysts and high isomer selectivity (53.0% of C6 isomers at 440 °C). By the strong metal-support interaction, the Pt/TiO2 was turned out as the best catalyst with great thermal stability as well as high reaction rate and product selectivity in high-temperature reforming reaction.

One-step hydrodeoxygenation of palm oil to isomerized hydrocarbon fuels over Ni supported on nano-sized SAPO-11 catalysts

Nano-sized SAPO-11s were hydrothermally synthesized with using di-n-propylamine (DPA) as structure-directing agent in mixed n-tetradecanoamine–n-propanol–H2O medium and the Ni/SAPO-11 catalysts were prepared by incipient wetness impregnation. The catalysts was characterized by XRD, SEM, BET, H2-TPR, NH3-TPD and TG techniques and their catalytic performance was tested in hydrodeoxygenation (HDO) of palm oil to hydrocarbon fuels. Surfactant n-tetradecanoamine could mediate the minimum SAPO-11 sizes into 20–50nm. As comparing to the commercial SAPO-11, the nano-sized SAPO-11s presented significantly enlarged surfaces and mesoporous volumes, which offered sufficient space and strong interactions for dispersing Ni. One-step HDO of palm oil demonstrated that the nano-sized SAPO-1 supported Ni catalysts showed the high yield (80%) of liquid hydrocarbons, high isomerization selectivity (80%) and excellent stability due to that the catalyst presented appropriate acidity, higher Ni dispersity, balance of metal (Ni) and acid (SAPO-11) functionalities and fast diffusion for bulky palm oil and products. These promotion effects observed over the nano-sized SAPO-11 supported Ni catalysts indicated the potential application in biorefinery of vegetable oils to hydrocarbon fuels.

Role of nanosized oxide in catalysis on the nanoporous surface of zeolite particles

Based on our studies on the hybrid catalysts of nanosized (ns) oxide with zeolite, products obtained from the isomerization and hydrocracking of heavier n-paraffins and the role of ns oxide were investigated using a tricomponent catalyst of [Ni-Mo/γ-Al2O3], ns oxide, and H-beta zeolite catalyst, which showed high activity, high isomerization selectivity, and mild cracking ability. A concerted effect of the three components was observed. From the observed hybridization state of the catalyst, it was suggested that the concerted effect was obtained because the components become attached to each other. The individual and concerted effects of each component and two components, respectively, were investigated based on the ratio of [Ni-Mo/γ-Al2O3]/[H-beta zeolite], the content of ns oxide, the amount of metal, the type of ns oxide species, and the reduction state of metal. It was confirmed that in order to obtain the highest concerted effect, the ratios of [Ni-Mo/γ-Al2O3]/[H-beta zeolite] and/or ns oxide/zeolite are important. Furthermore, among the ns oxide species, nsAl2O3-nsTiO2 displayed the highest activity and cracking ability with an over-cracking suppression. In addition to increasing the concerted effect in the tricomponent catalyst, the performance of this catalyst could also be further increased by controlling the amount and reduction state of metal.

Alkylphosphonic acid- and small amine-templated synthesis of hierarchical silicoaluminophosphate molecular sieves with high isomerization selectivity to di-branched paraffins

This article proposes a one-step strategy to hydrothermally synthesize SAPO-11 with hierarchical micro- and meso-porous structure. The structure and acidity properties and the isomerization performance of the resulting hierarchical SAPO-11 were extensively characterized and assessed, respectively, and compared with those of a microporous SAPO-11. The results showed that the SAPO-11 with mutually interpenetrating micropores and mesopores had been obtained by introducing tetradecylphosphoric acid into the synthesis system of microporous SAPO-11. Compared with microporous SAPO-11, the hierarchical SAPO-11 had much higher external surface and mesoporous volume, and more active sites with suitable Brönsted acid strength. These advantages endowed the hierarchical SAPO-11-based catalyst with superior isomerization activity, enhanced selectivity to di-branched products, and decreased cracking selectivity. The strategy proposed opens a new route to synthesizing a variety of hierarchical mesoporous SAPO molecular sieves for size-selective catalytic conversions of relatively large hydrocarbon molecules.