Catalysts For Hydroisomerization Research Articles

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.

Reaction pathways control of long-chain alkanes hydroisomerization and hydrocracking via tailoring the metal-acid sites intimacy

Designing a bifunctional catalyst to achieve efficient hydroisomerization of long-chain alkanes is very essential for producing high-performance fuel and lubricant base oils. Herein, a bifunctional catalyst composed of an intimate mixture of ZSM-48 zeolite and alumina binder and with platinum (Pt) metal controllably deposited on zeolite or alumina was fabricated by a strong electrostatic adsorption method. The dependence of reaction pathways of hydroisomerization and hydrocracking of n-hexadecane on the metal-acid sites intimacy was investigated. High Brønsted acid density and suitable metal-acid sites intimacy favored to promote the catalytic activity. The selectivity, hydroisomerization mechanism and hydrocracking mechanism were significantly altered by tailoring the metal-acid sites intimacy. Too large or too small metal-acid sites intimacy was conducive to inhibit the occurrence of pore-mouth mode. A linear decease of the hydroisomerization selectivity with the increase of acid steps (nas) was observed. The catalyst with nanoscale intimacy of metal-acid sites (Pt/A-48) showed the highest catalytic activity and isomer selectivity (87%) and the least acid steps (nas = 1.4). This work provides a promising approach to fabricating highly efficient and shape-selective bifunctional catalysts for selective hydroisomerization of long-chain alkanes. A reaction network was proposed over the catalysts with different metal-acid intimacy.

Toward Superior Hydroisomerization Catalysts through Thermodynamic Optimization

Toward Superior Hydroisomerization Catalysts through Thermodynamic Optimization

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.

Full-crystalline monolithic EU-1 zeolite: sustainable synthesis and its applications in the hydroisomerization of ethylbenzene with meta-xylene

A novel strategy for the effective production of monolithic EU-1 zeolite as an active component of catalyst in C8 hydroisomerization.

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.

In‐situ Synthesis of Gallium‐Containing SAPO‐11 Molecular Sieves and Superior Catalytic Performance of Their NiWS Supported Catalysts for Hydroisomerization of n‐Hexadecane

AbstractIn order to prepare a high‐performance SAPO‐11 (silicoaluminophosphate‐11) based non‐noble metal supported catalyst for the hydroisomerization of long‐chain n‐alkanes, gallium‐modified SAPO‐11 molecular sieve was successfully synthesized by the in‐situ synthesis method, and the NiWS supported catalyst was prepared for the hydroisomerization of n‐hexadecane. The effects of Ga‐modification on the physicochemical properties of SAPO‐11 molecular sieve, the active phase properties, and the catalytic performance of the catalyst were studied. Through a series of physicochemical characterizations, it was found that the introduction of Ga increased the mesoporous volume of SAPO‐11 molecular sieve, reduced their acid density and strength, but improved the amount of medium‐strong Brønsted acid. The Ga‐modification weakened the interaction between the active metals and the support, increased the sulfidation degree of active metals, and increased the stacking number and dispersion of active phase. The results of catalytic performance evaluation showed that the catalytic activity and isomerization selectivity of the Ga‐modified SAPO‐11 molecular sieve based catalysts were improved, and the yield of i‐hexadecane of NiW/2Ga‐SAPO‐11 was the highest, which was 40.30 % higher than that of NiW/SAPO‐11. By analyzing the distribution of isomeric products, it was found that the Ga‐modified SAPO‐11 molecular sieve was helpful in improving the hydroisomerization depth of n‐hexadecane over the catalyst.

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.

Promoting hydroisomerization selectivity using channel axis reduced ZSM-48 fabricated by a combined bead-milling and porogen-assisted recrystallization method

ZSM-48 is a unidimensional zeolite that is frequently used as acid component of bi-functional hydroisomerization catalyst. As selectivity towards unwanted cracking products increases with retention time of isomerized products inside micropores, shortening their retention time inside the micropores by reducing channel length offers an effective way to improve isomerization selectivity. Direct synthesis of unidimensional zeolitic crystals with reduced channel axis is particularly difficult, since they habitually grow into rod-like shape along their channel direction. Post-synthetic bead-milling is a cost effective, mechanochemical method to decrease crystal size of zeolites from micro meter to nano meter scale, but suffers from amorphization or partial destruction of zeolitic crystals. Consequently, a post-milling recrystallization process is often entailed to remedy the destructed domains, which, nonetheless, readily causes secondary crystal growth and formation of bulky crystals that compromises the effect of bead-milling. Here, we show that porogen-assisted recrystallization can overcome the problem to fabricate channel axis reduced ZSM-48 nanocrystals. The Si/Al ratio is tunable between 30 and 200 and the acidity is largely preserved after recrystallization. The catalytic advantages of the obtained material are demonstrated in catalytic n-heptane hydroisomerization. The obtained ZSM-48 nanocrystal with Si/Al ratio of 100 outperforms the rest samples and shows enhanced isomerization yield (72% vs 62%) with respect to the parent sample. By combined diagnoses of the impact of diffusion length on product selectivity (product shape selectivity) and kinetic studies, selectivities to monomethyl branched isomers (2-methyl hexane and 3-methyl hexane) and small bulky dimethyl branched isomers (2,3- and 2,4-dimethyl pentane) are attributed to product shape selectivity, whereas the formation to bulky dimethyl branched isomers (2,2- and 3,3-dimethyl pentane) is hindered mainly by transition-state shape selectivity. The combined destructive-constructive synthetic protocol and the revelation of the origin of shape-selectivity in n-heptane hydroisomerization are useful for hydroisomerization catalyst design.

Synthesis of nano-sized small-crystal and hierarchical SAPO-11 molecular sieves and superior catalytic performance of their NiWS-supported catalysts in hydroisomerization of n-hexadecane

The nano-sized small-crystal and hierarchical SAPO-11 molecular sieves were successfully synthesized with l-Lysine as the crystal growth inhibitor, and their particle size reached 80 nm at the minimum, and the crystal size was 22.1 nm. With the synthesized SAPO-11 molecular sieve as support, the corresponding NiW supported catalyst was prepared for the hydroisomerization of n-hexadecane. The properties of small-crystal and hierarchical SAPO-11 molecular sieve and catalyst were analyzed by a series of physicochemical characterizations, and the formation mechanism of small-crystal and hierarchical SAPO-11 molecular sieve was proposed. The results showed that the reduction of crystal size greatly improved the BET specific surface area, mesopore volume of SAPO-11 molecular sieve. The decrease of crystal size increased the surface Si content of SAPO-11 molecular sieve, thus improving the surface acidity of SAPO-11 molecular sieve, and weakening the interaction between active metals and supports of the catalysts. In addition, the decrease of crystal size increased the dispersion and stacking number of the active phases, thus greatly improving the catalytic performance of the catalysts. Compared with the catalyst corresponding to the conventional SAPO-11 molecular sieve, the yield of i-hexadecane of the catalyst corresponding to small-crystal and hierarchical SAPO-11 molecular sieve increased by 45.34%.

Small-crystal and hierarchical SAPO-11 molecular sieve synthesized via three-stage crystallization method and hydroisomerization performance of corresponding NiWS supported catalyst

In order to prepare non-noble metal supported hydroisomerization catalyst with high catalytic performance, this work first proposed a novel three-stage crystallization method to synthesize small-crystal and hierarchical SAPO-11 molecular sieve, and prepared the corresponding NiWS supported catalyst for the hydroisomerization of n-hexadecane. The physicochemical properties of the small-crystal and hierarchical SAPO-11 molecular sieve and the NiWS supported catalyst were analyzed via a series of characterization methods. It was found that the crystal size of SAPO-11-S was reduced to 21.8 nm and the particle size was reduced to 70–140 nm. SAPO-11-S was superior to SAPO-11-C in pore properties and acidity. The reason for the increase of the number of medium-strong B acid sites in SAPO-11-S was investigated by 29Si MAS NMR characterization, and the formation mechanism of SAPO-11-S was proposed by tracking and analyzing the crystallization process of SAPO-11-S. The decrease of crystal size of SAPO-11 molecular sieve effectively improved the sulfidation degree of active metals and the dispersion degree of the active phase of the catalyst, and promoted more active phases to form “type II active phase”. Compared with NiW/SAPO-11-C, NiW/SAPO-11-S showed higher catalytic activity and isomerization selectivity, and the maximum i-hexadecane yield of NiW/SAPO-11-S was 44.77% higher than that of NiW/SAPO-11-C.

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.

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.

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.

Superior Activity and Isomerization Selectivity of Structural Defects on Nanosized Zsm-22-Assisted Ni Clusters Compared with Commercial Pt Catalysts in N-Dodecane Hydroisomerization

Superior Activity and Isomerization Selectivity of Structural Defects on Nanosized Zsm-22-Assisted Ni Clusters Compared with Commercial Pt Catalysts in N-Dodecane Hydroisomerization

Pt@SAPO-11 bifunctional catalysts with spatial architecture constructed via a seed-directed solvent-free strategy for n-dodecane hydroisomerization

Inferior sintering-resistance of metal nanoparticles is an obstacle restricting the development of bifunctional catalysts in chemical industry. The construction of spatial architecture in zeolitic framework can enhance the stability of metal nanoparticles and prolong the service life of catalysts. A seed-directed solvent-free strategy was proposed here to prepare a metal-confined catalyst along the zeolitic framework to sterically encapsulate metal nanoparticles. The use of raw materials without extra solvents could improve synthetic efficiency of each kettle, reduce economic cost and decrease environmental pollution caused by organic solvents. The status of metal species was observed by aberration-corrected TEM images and XPS spectra, and the intracrystalline Pt species were speculated to isomorphically substitute the framework Al and P or occupy tens of micropore to form structural defect sites, leading to a decrease in the support acidity and a better balanced bifunctionality. While enhancing the metal stability, the maximum yield of isomer products was increased to 75% versus 63% for the conventional specimen synthesized by hydrothermal and post-impregnated method on n-dodecane hydroisomerization. The results provide an efficient route to the synthesis of alternative bifunctional catalysts for n-alkanes hydroisomerization, and promote the high value-added conversion of downstream products in coal/natural gas chemical industry.

A Review on the Hydroisomerisasion of n-Parafins over Supported Metal Catalysts

Catalytic hydroisomerization of n-paraffin aims to produce branched paraffin isomers and suppress cracking reactions in the production of the low cloud point of biodiesel. The development of the type of metal and catalyst support, amount of metal loading, and reaction conditions are important to increase the catalyst activity. A high performace catalyst for hydroisomerization bears bifunctional characteristics with a high level of hydrogenation active sites and low acidity, maximizing the progress of hydroisomerization compared to the competitive cracking reaction. In addition, a catalyst support with smaller pore size can hinder large molecular structure isoparaffins to react on the acid site in the pore thus providing good selectivity for converting n-paraffin. Catalysts loaded with noble metals (Pt or Pd) showed significantly higher selectivity for hydroisomerization than non-noble transition metals such as Ni, Co, Mo and W. The reaction temperature and contact time are also important parameters in hydroisomerization of long chain paraffin, because long contact times and high temperatures tend to produce undesired byproducts of cracking. This review reports several examples of supported metal catalyst used in the hydroisomerization of long chain hydrocarbon n-paraffins under optimized reaction conditions, providing the best isomerization selectivity results with the lowest amount of byproducts. The role of various metals and their supports will be explained mainly for bifunctional catalysts.

Mesoporous Ni–Cu/WOx/ZrO2 Catalyst with Highly Dispersed WOx Clusters: Efficient Catalysts for Selective Hydroisomerization of Isobutane to n-Butane

A series of mesoporous Ni–Cu/WO3/ZrO2 (1Ni1Cu/mWZr) was successfully prepared with F127 as a template and used as catalysts for isobutane hydroisomerization to n-butane. The effects of the F127/ZrO...

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.

Advanced Study of Promoted Pt /SAPO-11 Catalyst for Hydroisomerization of the n-Decane Model and Lube Oil

SAPO-11 is synthesized from silicoaluminophosphate in the presence of di-n-propylamine as a template. The results show that the sample obtained has good crystallinity, 396m2/g BET surface area, and 0.35 cm3/g pore volume. The hydroisomerization activity of (0.25)Pt (1)Zr (0.5)W/SAPO-11 catalyst was determined using n-decane and base oil. All hydroisomerization experiments of n-decane were achieved at a fixed bed plug flow reactor at a temperature range of 200-275°C and LHSV 0.5-2h-1. The results show that the n-decane conversion increases with increasing temperature and decreasing LHSV, the maximum conversion of 66.7 % was achieved at temperature 275°C and LHSV of 0.5 h-1. Meanwhile, the same catalyst was used to improve base oil specification by increasing viscosity index and decreasing pour point. The isomerization reaction conditions, employed are temperature (200-300)ºC, the liquid hourly space velocity of 0.5-2h-1, and the pressure kept atmospheric. The present study shows that Pt Zr W/SAPO-11 minimizes the pour point of lubricating oil to -16°C at isomerization temperature of 300°C and LHSV of 0.5 h-1 and viscosity index 134.8.