Rare Earth Metals Ion-exchanged β-Zeolites as Supports of Platinum Catalysts for Hydroisomerization of n-Heptane

A series of Pt catalysts supported on the Hβ-zeolite that is ion-exchanged with the rare earth metal ions of Ce（III） and La（III）,are prepared by impregnation,characterized by inductively coupled plasma （ICP）,X-ray diffraction （XRD）,BET,temperature-programmed desorption of ammonia （NH3-TPD）,temperature-programmed reduction of hydrogen （H2-TPR） and H2-chemisorption techniques,and evaluated in the hydroisomerization of n-heptane with an atmospheric fixed-bed reactor.The reaction temperature,time on stream,space velocity,and the ratio of H2/n-heptane are changed to get the optimal conditions.The Ce（III） and La（III）-exchanged Hβ-zeolites exhibit higher selectivity for isomerized products than the neat Hβ-zeolite.Moreover,the Ce（III）-exchanged catalysts give higher conversions of n-heptane,whereas the La（III）-exchanged ones do not show any improvement in con-version.Under optimal conditions,the catalyst with 0.4% （by mass） Pt and 0.5% （by mass） Ce loading presents very high selectivity of isomerized products of 95.1% coupled with high n-heptane conversion of 68.7%.Effects of the ion-exchange of Ce（III） and La（III） on the catalytic performance are discussed in relation with the physico-chemical properties of catalysts.

Hydroisomerization of n-heptane on Pt promoted phosphomolybdate catalysts

Phospbomolybdate （PMo） with varying Mo loadings ranging from 5-30 wt% on alumina were prepared by incipient wetness impregnation method. 0.5 wt% of Pt was further loaded in order to prepare the bifunctional （metal-acid） Pt-PMo/Al2O3 catalysts. Thus prepared catalysts showed very high catalytic activities for n-heptane hydroisomerization compared with Pt impregnated MoO3 catalysts supported either on Al2O3 or on AIPO4. The conversion of n-heptane increased with Mo loading up to 20 wt% and slightly decreased with further Mo loading. However, the selectivity towards isomers showed an increasing trend up to 30 wt% of Mo in the catalyst. A relationship between catalytic activity and acidic strength was established in the present study.

Hydroisomerization of n-heptane over bimetal-bearing H_3PW_(12)O_(40) catalysts supported on dealuminated USY zeolite

The bimetal-bearing (CePt or LaPt) 12-tungstophosphoric acid (H3PW12O40 (PW)) catalysts supported on dealuminated USY zeolite (DUSY) were prepared by impregnation and characterized by XRD, BET, IR, and H2-chemisorption. Their catalytic activities were tested in the hydroisomerization of n-heptane with a continuous atmospheric fixed-bed reactor. After the steam treatment combined with the acid leaching, as well as the supporting with PW and the bimetals, the DUSY support retains the Y zeolite porosity and the PW well keeps its Keggin structure in catalysts. The doping of Ce into the catalysts enhances the dispersion of Pt on the catalyst surface. The Pt-bearing PW catalysts doped with Ce or La, especially Ce, exhibit much higher catalytic activity and selectivity than the catalysts without dopants at lowered reaction temperatures. At the optimal reaction conditions, i.e., the reaction temperature of 250℃ and WHSV of 1.4 h1, the catalyst with a Pt loading of 0.4%, PW loading of 10% and a molar ratio of Ce to Pt of 15:1 shows a conversion of n-heptane of 70.3% with a high selectivity for isomerization products of 94.1%.

HZSM-5 zeolites undergoing the high-temperature process for boosting the bimolecular reaction in n-heptane catalytic cracking

High-temperature treatment is key to the preparation of zeolite catalysts.Herein,the effects of hightemperature treatment on the property and performance of HZSM-5 zeolites were studied in this work.X-Ray diffraction,N2physisorption,27Al magic angle spinning nuclear magnetic resonance(MAS NMR),and temperature-programmed desorption of ammonia results indicated that the hightemperature treatment at 650℃ hardly affected the inherent crystal and texture of HZSM-5zeolites but facilitated the conversion of framework Al to extra-framework Al,reducing the acid site and enhancing the acid strength.Moreover,the high-temperature treatment improved the performance of HZSM-5 zeolites in n-heptane catalytic cracking,promoting the conversion and light olefins yield while inhibiting coke formation.Based on the kinetic and mechanism analysis,the improvement of HZSM-5 performance caused by high-temperature treatment has been attributed to the formation of extra-framework Al,which enhanced the acid strength,facilitated the bimolecular reaction,and promoted the entropy change to overcome a higher energy barrier in n-heptane catalytic cracking.

OSDA-free synthesis of FeZSM-22 zeolite from natural minerals for n-octane hydroisomerization

A seed-directed approach to synthesizing Fe ZSM-22 zeolite without organic structure directing agent(OSDA)was developed by using Fe-rich diatomite as all aluminum and iron sources.The Fe ZSM-22zeolite with optimal crystallinity and purity can be obtained by systematically adjusting feed composition and synthesis conditions.Characterizations show that Fe ZSM-22 zeolite synthesized with OSDA-free owns high crystallinity,obvious thin needle-shaped morphology and high Bronsted/Lewis acid ratio.Significantly,when used for n-octane hydroisomerization reaction,its derived catalyst exhibits the best catalytic performance reflected by the highest selectivity to C_(8)isomers compared to the two reference catalysts prepared based on a Fe-containing and a Fe-free ZSM-22 synthesized through an OSDA-directed route from natural diatomite and conventional chemicals,respectively.This work provides an alternative route to sustainably synthesizing heteroatomic zeolites with high performance.

Synthesis of Pt/PMA-MIL-101 Catalyst and Its Performance in n-Heptane Isomerization

Hydroisomerization of n-heptane is an efficient method for producing gasoline with a high octane number.The focus of this study was to find a highly efficient catalyst that could both promote the conversion of n-heptane and inhibit the cracking side reaction.MIL-101(Cr)is a chromium-based metal-organic framework(MOF)with good hydrothermal stability,and exhibits a three-dimensional pore structure that is similar to that of zeolites.Using phosphomolybdic acid(PMA;H3PMo12O40·xH2O)can increase the number of Brønsted acid sites on MIL-101(Cr),which contributes to improving the catalytic performance during isomerization.In this study,0.4%Pt/PMA-MIL-101(Cr)catalyst was successfully crystallized at 220℃using a hydrothermal synthetic method.The results showed that the synthesized samples were mesoporousmicroporous composite materials with the typical octahedral structure,and the MIL-101(Cr)framework was not damaged following modification with PMA.It was found that 0.4%Pt30%PMA-MIL-101(Cr)exhibited the best performance for isomerization of n-heptane,with a conversion rate and selectivity at 260°C of 47.6%and 96.6%,respectively.After five hours of reaction,the conversion rate and selectivity of the catalyst remained above 38%and 80%,respectively.

Reactive Molecular Dynamics Simulation on Thermal Decomposition of n-Heptane

The thermal decomposition of n-heptane is an important process in petroleum industry. The theoretical investigations show that the main products are C2H4, H2, CH4, and C3H6, which agree well with the experimental results. The products populations depend strongly on the temperature. The quantity of ethylene increases quickly as the temperature goes up. The conversion of n-heptane and the mole fraction of primary products from reactive molecular dynamic and chemical kinetic modeling are compared with each other. We also investigated the pre-exponential factor and activation energy for thermal decomposition of n-heptane by kinetic analysis from the reactive force field simulations, which were extracted to be 1.78×10^14 s^-1 and 47.32 kcal/mol respectively.

利用n-heptane详细模型对水乳化柴油燃烧的化学动力学研究

以4100QBZL-2型直喷柴油机为模拟对象,采用化学动力学计算软件CHEMKIN与LLNL的n-heptane详细氧化模型为基础,对柴油机燃用纯柴油,10%、20%、30%的水乳化柴油进行化学动力学模拟。数值模拟结果表明:水乳化柴油带来的滞燃期延长、着火滞后等现象,是乳化燃料中的水分在缸内的物理现象引起的。从纯化学动力学方面来看,掺入一定的水分可以促进H、O、OH、HO2等自由基在低温燃烧(LTC)阶段的生成,使得着火提前。通过敏感性分析可知,掺入的水分会对n-heptane氧LTC时期过氧烷基的异构化过程及过氧化氢酮的分解都会产生促进作用,从而导致n-heptane的快速分解及氧化。

Detailed Temperature-dependent Study of n-Heptane Pyrolysis at High Temperature

n-Heptane is the most important straight chain paramn in the fossil-fuel industry. In this work, pyrolysis behavior of n-heptane at high temperature is investigated by a se- ties of ReaxFF based reactive molecular dynamics simulations. Temperature effects on the n-heptane pyrolysis and related products distributions have been detailedly analyzed. The simulation results indicate that the temperature effect is characterized in stages. High tern- perature can accelerate the decomposition of n-heptane, but the influence becomes small after it reaches a certain level. According to the different reaction behaviors, pyrolysis of n-heptane could be divided into three stages. The variation trends of the mass fraction evolu- tion of ethylene （C2H4）, C3, and C4 calculated from reactive molecular dynamics simulations are in good agreement with the previous experimental results. The apparent activation en- ergy extracted from the first-order kinetic analysis is 53.96 kcal/mol and a pre-exponential factor is 55.34×10^13 s-1, which is reasonably consistent with the experimental results.

Effect of preparation method on the bimetallic NiCu/SAPO-11 catalysts for the hydroisomerization of n-octane

The bimetallic NiCu/SAPO-11 catalysts were prepared by co-impregnation, sequential impregnation, coprecipitation, and mechanical mixing methods. Powder X-ray diffraction, nitrogen adsorption-desorption,temperature-programmed desorption of ammonia, transmission electron microscopy, temperatureprogrammed reduction of hydrogen, and X-ray photoelectron spectroscopy were used to characterize the physicochemical properties of the catalysts. The catalytic performance of the catalysts was assessed by the hydroisomerization of n-octane. Results indicated that the conversion of n-octane and selectivity to n-octane isomers were related to the preparation methods of the catalysts. The catalysts with Ni-Cu alloy effectively restrained the hydrogenolysis reaction that decreases the selectivity of isomerization. The catalyst prepared by the mechanical mixing of NiO and CuO hardly formed Ni-Cu alloy, showing obvious hydrogenolysis and low selectivity to n-octane isomers. The unbalance between the metal and acid sites resulted in the low conversion of n-octane and selectivity to n-octane isomers. Among all the catalysts,the catalyst prepared by the co-impregnation method exhibited high catalytic activity and selectivity to n-octane isomers.

Hydroisomerization performance of platinum supported on ZSM-22/ZSM-23 intergrowth zeolite catalyst

Hydroisomerization catalysts Pt/ZSM-22, Pt/ZSM-23, and Pt/ZSM-22/ZSM-23 were prepared by supporting Pt on ZSM-22, ZSM-23, and intergrowth zeolite ZSM-22/ZSM-23, respectively. The typical physicochemical properties of these catalysts were characterized by X-Ray Diffraction （XRD）, N2 absorption-desorption, Pyridine-Fourier Transform Infrared （Py-FTIR）, Transmission Electron Microscopy （TEM）, X-Ray Fluorescence （XRF）, Scanning Electron Microscopy （SEM） and NH3- Temperature Programmed Desorption （NH3-TPD）, and the performance of these catalysts in n-dodecane hydroisomerization was evaluated in a continuous down-flow fixed bed with a stainless steel tubular reactor. The characterization results indicated that the intergrowth zeolite ZSM-22/ZSM-23 possessed the dual structure of ZSM-22 and ZSM-23, and the catalyst Pt/ZSM-22/ZSM-23 had similar pores and weak acidity to Pt/ZSM-22 and Pt/ZSM-23 catalysts. Moreover, Pt/ZSM-22/ZSM-23 catalyst showed a high selectivity in hydroisomerization of long chain n-alkanes to mono-branched isomers. The evaluation results for n-dodecane hydroisomerization indicated that the activity of Pt/ZSM-22/ZSM-23 was the lowest, while the hydroisomerization selectivity was the highest among the three catalysts. The maximum yield of i-dodecane product was 68.3% over Pt/ZSM-22/ZSM-23 at 320 ℃.

Synthesis of MOR/SAPO-11 Composite Molecular Sieve via Seed Crystallization for n-Alkane Hydroisomerization

n-Alkane isomerization is a critical reaction that can affect parameters in oil refining, such as the gasoline octane number and diesel oil solidifying point. In this study, a catalyst support, mordenite (MOR)/silicoaluminophosphate (SAPO)-11 composite zeolite with core/shell structure, was synthesized by hydrothermal method with MOR acting as the seed for crystallization. The crystal structure, elemental composition, surface area, pore volume, and acidity of the catalyst was thoroughly characterized. In addition, the catalytic performance of the as-obtained Pt/MOR/SAPO-11 in the hydroisomerization of n-dodecane was tested. The results indicated that the properties and catalytic performance of the composite molecular sieve were quite different from those of the pure zeolites and physical mixture of MOR and SAPO-11 (MOR+SAPO-11). Compared with the physical mixture, MOR and SAPO-11 were more tightly bound in MOR/SAPO-11 because of chemical bonding. Moreover, the acidity and pore structure were favorable to the catalytic hydroisomerization of n-dodecane. Pt/MOR/SAPO-11 exhibited higher isomerization activity than the Pt-loaded pristine MOR and MOR+SAPO-11. Thus, the core-shell composite molecular sieve has promising industrial applications as the catalyst support.

Effect of silicon precursor on silicon incorporation in SAPO-11 and their catalytic performance for hydroisomerization of n-octane on Pt-based catalysts

SAPO-11 molecular sieves were synthesized using silica sol, hydrophilic fumed silica, and tetraethyl orthosilicate（TEOS） as silicon precursors. Their physicochemical properties were characterized using XRD,SEM, nitrogen adsorption-desorption, Py-IR, NH;-TPD, EDS, and;Al,;P,;Si MAS NMR techniques. The catalytic performance was assessed in the hydroisomerization of n-octane. The results showed that the silicon precursors influenced the physicochemical properties and catalytic performance of SAPO-11. SAPO-11 synthesized using hydrophilic fumed silica as silicon precursor showed higher silicon distribution and had more medium acid sites. SAPO-11 synthesized using TEOS as silicon precursor had more silicon content, but more silicon islands formed in its framework. The depolymerization of silicon precursors might affect the silicon content and distribution in SAPO-11. In the hydroisomerization of n-octane, the catalytic activity strongly depended on the number of medium acid sites instead of the number of total acid sites.SAPO-11 synthesized using hydrophilic fumed silica as silicon precursor exhibited higher catalytic activity than the other samples because it has more medium acid sites.

Creating mesopores in ZSM-48 zeolite by alkali treatment: Enhanced catalyst for hydroisomerization of hexadecane

ZSM-48 zeolites with various Si/Al ratios were hydrothermally synthesized in the H;N（CH;）;NH;（HDA）-containing media. The obtained samples were highly crystallized with minor mixed phases as evidenced by X-ray powder diffraction（XRD）. The alkaline treated ZSM-48 zeolites maintained its structure under different concentrations of Na OH aqueous solution. Micropores remained unchanged while mesopores with wide pore size distribution formed after the alkaline treatment. The surface area increased from 228 to 288 m;/g. The Br?nsted acid sites had little alteration while an obvious increase of Lewis acid sites was observed. The hydroisomerization of hexadecane was performed as the model reaction to test the effects of the alkali treatment. The conversion of hexadecane had almost no change, which was attributed to the preservation of the Br?nsted acid sites. While high selectivity to iso-hexadecane with an improved iso to normal ratio of alkanes was due to the mesopore formation and improved diffusivity.

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 Bronsted 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.

Study on Synthesis of Mesoporous M-MCM-48(M=Zr,Mg) and Its Activity for Isomerization of n-Heptane

The mesoporous materials supported zirconium （Zr-MCM-48） and magnesium （Mg-MCM-48） with three-dimen- sional pore structures and different Zr or Mg contents were prepared via the hydrothermal method, respectively. The prepared samples were characterized by means of X-ray diffraction （XRD）, scanning electron microscope （SEM）, transmission electron microscope （TEM）, Fourier transform infrared spectroscopy （FT-IR）, NH3 temperature programmed desorption （NH3-TPD） and N2 adsorption-desorption. The XRD, TEM and N2 adsorption-desorption results suggested that M-MCM-48 （where M = Zr, Mg） samples still maintained typical cubic mesoporous framework of MCM-48, with slight decrease of specific surface areas and mesopore orders. The isomerization of n-heptane was carried out as a probe reaction at various factors including the zirconium or magnesium content, reaction time, reaction temperature and weight hourly space veloc- ity （WHSV）. Preliminary results demonstrated that the Mg-MCM-48 catalyst exhibited a higher catalytic activity with a maximum heptane conversion of 91.5% and a corresponding isomerization selectivity of 72.3% as compared to that of Zr- MCM-48. However, for catalytic stability of Mg-MCM-48 for n-heptane isomerization was poorer than Zr-MCM-48, because the Mg-MCM-48 catalyst could maintain a relatively high catalytic activity for only 130 rain, while the Zr-MCM-48 catalyst could maintain a relatively high catalytic activity for more than 190 min without any obvious decrease in performance.

Experimental and kinetic study of n-heptane isomerization on nanoporous Pt-(Re,Sn)/HZSM5-HMS catalysts

Pt-（Sn,Re）/HZSM5-HMS catalysts were evaluated for n-heptane isomerization at 200–350 ℃.To characterize the catalyst,X-ray diffraction,X-ray fluorescene,Fourier transform infrared spectroscopy,ultraviolet-visible diffuse reflectance spectroscopy,temperature-programmed reduction of H2,temperature-programmed desorption of NH3,infrared spectroscopy of adsorbed pyridine,H2 chemisorption,nitrogen adsorption-desorption,scanning electron microscopy and thermogravimetric analysis were performed.Kinetics of n-C7 isomerization were investigated under various hydrogen and n-C7 pressures,and the effects of reaction conditions on catalytic performance were studied.The results showed that bi-and trimetallic catalysts exhibit better performance than monometallic catalysts for this reaction.For example,a maximum i-C7 selectivity（ 〉74%） and multibranched isomer selectivity（40%） were observed for Pt-Sn/HZSM5-HMS at 200 ℃.

Catalytic performance of Pt/HY-β in n-octane hydroisomerization

A bifunctional catalyst Pt/HY-β was prepared from a bimicroporous composite zeolite Y-β. Characterization results showed that the specific surface area, pore volume, and acid amount of the catalyst Pt/HY-β all decreased compared to the original zeolite. The catalytic performance of this catalyst in n-octane hydroisomerization was investigated in a fixed bed stainless steel tubular reactor. The results showed that at a hydrogen/n-octane volume ratio of 1000, pressure of 0.6 MPa, temperature of 230 ℃ and LHSV of 3 h^-1, the conversion of n-octane, yield of liquid, hydrocracking rate and yield of iso-octane were 52.32%, 88.66%, 12.60%, 39.51%, respectively.

Effect of metal content on the activity and product selectivity of n-decane hydroisomerization over Ni-Pd/HY zeolite

Metal-loaded zeolite catalysts were synthesized and examined in the hydroisomerization of n-decane.Specifically,zeolite Y was impregnated with 0.1 wt%Pd and varying amounts of Ni（0.1-0.5 wt%].The crystallinity of the metal-loaded catalysts was characterized by X-ray diffraction,and the average metal particle size was determined by transmission electron microscopy.The states of Pd and Ni were identified by X-ray photoelectron spectroscopy.Ammonia temperature-programmed desorption analysis revealed the occurrence of ion-exchange of some of the catalyst acid sites with Ni-（2＋）.The reducibility of the HY zeolite-supported Pd,Ni,and Pd-Ni catalysts was studied by temperature-programmed reduction.The hydroisomerization of n-decane over the prepared catalyst was conducted at 200-450℃ under 1 atm.Ni addition of up to 0.3 wt%over 0.1 wt%Pd/HY enhanced the n-decane conversion and isomerization product selectivity.The improved selectivity of the mono- and dibranched isomers suggested the occurrence of a protonated cyclopropane intermediate mechanism.However,further Ni addition above 0.3 wt%considerably reduced the activity and isomerization selectivity.The bimetallic catalysts were more selective toward the formation of dibranched isomers,i.e.,those containing a higher octane number.

A Promising MoO_x-based Catalyst for n-Heptane Isomerization

The SiO2 and g-Al2O3 supported MoOx catalyst and a MoOx-SiO2 catalyst have been studied in a conventional fixed-bed flow reactor for n-alkanes isomerization. It is shown that the MoOx-SiO2 catalyst with SiO2 framework, in which the bulk MoOx phase is large enough to form typical mesoporous structure, is promising in terms of its advantages of both improved mechanical strength and high catalytic properties over the supported MoOx and bulk MoOx catalyst.