Conversion Of N-heptane Research Articles

Modification of the catalytic properties of MoO2−x(OH)y dispersed on TiO2 by Pt and Cs additives

Addition of 5% Pt or alkali metals such as K or Cs each separately to the bifunctional MoO2−x(OH)y catalyst results in modification of the chemical structure of this system, especially in the case of alkali metals. A new MoO2−x(OA)y, AK, Cs, monofunctional structure having only metallic properties is formed. In the case of Cs for example, the MoOCs bond formation takes place in the course of the reduction process of MoO3 to MoO2 by hydrogen hinders the acidic BrØnsted MoOH formation, which usually is formed in this system. Characterization by surface XPS–UPS, ISS and FT-IR spectroscopic techniques as well as catalytic activity carried out at the same experimental conditions confirm the presence of this monofunctional MoO2−x(OCs)y system. On the contrary, platinum addition enhances the metallic character of the MoO2−x(OH)y bifunctional system in terms of slight improvement in the conversion of 1-heptene and n-heptane as well as dehydrogenation of methylcyclohexane to toluene.

Catalytic reforming of n-heptane over Pt/Al-HMS catalysts

Pt catalysts supported on Al-HMS materials were prepared and characterized by XRD, NH3-TPD, TGA and pyridine-adsorbed FTIR techniques. Catalytic performance of samples was investigated for reforming of n-heptane and compared as a function of Al content. TPD measurements showed that the acidity of Al-HMS materials enhanced with the increasing Al content. Results showed that the ratio of BrÖnsted/ Lewis acidic sites decreased with the increasing Al content. The catalytic evaluation revealed that Pt/Al-HMS catalysts had a high activity for conversion of n-heptane. The distribution of products was described based on the nature of the acidic sites.

Hydroisomerization of benzene-containing gasoline fractions on a Pt/SO 4 2− -ZrO2-Al2O3 catalyst: II. Effect of chemical composition on acidic and hydrogenating and the occurrence of model isomerization reactions

The acidic and hydrogenating of Pt/SO 4 2− -ZrO2-Al2O3 samples containing from 18.8 to 67.8 wt % Al2O3 as a support constituent were studied by the IR spectroscopy of adsorbed CO and pyridine, and the model reactions of n-heptane and cyclohexane isomerization on these catalysts were examined. The total catalyst activity in the conversion of n-heptane decreased with the concentration of Al2O3; this manifested itself in an increase in the temperature of 50% n-heptane conversion from 112 to 266°C and in an increase in the selectivity of isomerization to 94.2%. In this case, the maximum yield of isoheptanes was 47.1 wt %, which was reached on a sample whose support contained 67.8 wt % Al2O3. A maximum yield (69.6 wt %) and selectivity (93.7%) for methylcyclopentane formation from cyclohexane were also reached on the above catalyst sample. This can be explained by lower concentrations of Lewis and Bronsted acid sites in the Pt/SO 4 2− -ZrO2-Al2O3 system, as compared with those in Pt/SO 4 2− -ZrO2. The experimental results allowed us to make a preliminary conclusion that the Pt/SO 4 2− -ZrO2-Al2O3 catalyst whose support contains 67.8 wt % Al2O3 is promising for use in the selective hydroisomerization of benzene-containing gasoline fractions in the thermodynamically favorable process temperature range of 250–300°C.

Catalytic cracking of n-heptane under activation of lattice oxygen in a circulating fluidized bed unit

A circulating fluidized bed unit was used to evaluate influences of lattice oxygen introduction over catalytic cracking of n-heptane over HZSM-5 catalyst in a continuous reaction fashion. The results demonstrated that V 2O 5/Al 2O 3, which functioned as lattice oxygen supplier, promoted conversion of n-heptane in a much larger extent, compared with fixed-bed reactor. It also improved yields of propylene and butylenes, and intensified formation of aromatics and coke. Besides lattice oxygen species, some adsorbed oxygen species also participated into the reaction. CO and H 2O were formed as main oxygenated products. Steam introduction improved selectivity of propylene and butylenes, promoted desorption of strong adsorbed species in V 2O 5/Al 2O 3, and thus formation of coke was depressed; however, the damage to HZSM-5 framework was aggravated simultaneously.

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 (NH 3-TPD), temperature-programmed reduction of hydrogen (H 2-TPR) and H 2-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 H 2/ 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 conversion. 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 physicochemical properties of catalysts.

Using β-MCM41 composite molecular sieves as supports of bifunctional catalysts for the hydroisomerization of n-heptane

β-MCM41 composite molecular sieves were hydrothermally synthesized using NaOH treated β zeolite as precursors, and Pt/β-MCM41 bifunctional catalysts were prepared by impregnation. Hβ, desilicated Hβ by NaOH treatment (Dβ), and the physical mixture of Hβ and MCM41 (β+MCM41) were also used as control supports for bifunctional catalysts. All the catalysts were characterized by ICP, XRD, BET, nitrogen adsorption–desorption isotherm and NH3-TPD, and evaluated in the hydroisomerization of n-heptane using an atmospheric fixed bed flow reactor. Dβ, β+MCM41, or β-MCM41 supported Pt catalysts showed higher selectivity to isoheptanes than the counterpart Pt/Hβ did due to the presence of mesopores in addition to the zeolite micropores. Moreover, Pt/β-MCM41 was demonstrated to be a much more selective catalyst among them because the connection between mesopores and micropores accelerated the diffusion of larger molecules of isoheptanes. Under optimal conditions, Pt/β-MCM41 provided a very high selectivity to isomerization of 96.5%, coupled with a considerable high conversion of n-heptane of 56.0%.

Catalytic cracking of n-heptane over HZSM-5 catalysts with the activation of lattice oxygen

Paraffin, one of the major components of straight-run naphtha, is relatively inert compared with olefin, which poses a difficulty for catalytic cracking of naphtha. The present study proposed introducing lattice oxygen into previous HZSM-5 catalyst system to improve conversion and light olefin selectivity. Vanadium oxide based catalyst was prepared separately as the lattice oxygen provider and then mixed with HZSM-5 catalyst for evaluation in a fixed-bed reactor using n-heptane as model compound. The results demonstrated that conversion of reactant increased from ∼51% to ∼59% by replacing 20% of HZSM-5 catalyst with V 2O 5/Al 2O 3; depending on different location of V 2O 5/Al 2O 3 relative to HZSM-5 catalyst in the reactor, conversion and product distribution varied significantly, while the addition of pure alumina did not have such an effect. Besides, water was formed in liquid products accompanied by reduction of V 5+ during the reaction, as revealed by FT-IR and XRD results, respectively; the oxidized V 5+ seemed to have greater capability in promoting conversion of n-heptane. Therefore, it was concluded that n-heptane could be activated by lattice oxygen provided by oxidized vanadia before further cracking over acidic sites in HZSM-5 catalyst.

Synthesis and Catalytic Performance of the Framework-Substituted Manganese β Zeolite

The framework-substituted manganese β zeolite was synthesized by an unseeded hydrothermal method, using manganese nitrate, colloidal silica, sodium aluminate, and tetraethylammonium hydroxide as raw materials. The optimized synthetic conditions were obtained by adjusting the key synthesis parameters, such as SiO2/Al2O3 ratio, TEAOH/SiO2 ratio, pH value, crystallization temperature, and SiO2/MnO ratio. The resulting samples were characterized by powder XRD, UV–vis spectroscopy, nitrogen physical adsorption, and ICP, which complementarily demonstrate the incorporation of manganese into the zeolite framework. Tested in hydroisomerization of n-heptane as a carrier for Pt catalyst, the Mn-incorporated sample showed a very high selectivity for isomerized products 94.7% with a high conversion of n-heptane 71.1% at 230 °C. UV–vis: Parent Al(60)β showed an adsorption band at 270 nm. Mn-containing samples showed a new intensive band at ca. 360 nm, it became more intensive with the increase of manganese content; no obvious absorption band occurred at ca. 500 nm which is assigned to the extra-framework manganese species in channels or on the surface. Mn-exchanged and Mn-loaded samples (curve b and curve c, respectively) showed no adsorption band at ca. 360 nm.

Alkaline earth metal ion-exchanged β zeolite supported Pt catalysts for hydroisomerization of n-heptane

Alkaline earth metal (Mg, Ca, Sr and Ba) ions were exchanged into Hβ zeolite, which were used as the supports to load the noble metal Pt to prepare bifunctional catalysts for hydroisomerization of n-heptane. The catalysts were characterized by ICP, XRD, BET, NH3-TPD, H2-TPR and H2-chemisorption techniques, and evaluated in an atmospheric fixed bed reactor. The catalysts promoted by the alkaline earth metals are revealed to present much higher selectivity to isomerization than the counterpart Pt/Hβ. Moreover, the Ba-bearing catalyst loaded with 0.4 wt% Pt and 5:1 molar ratio of Ba to Pt gives a very high selectivity to iso-heptanes 95.4% with a considerable high conversion of n-heptane 61.7%. The promotion effect of alkaline earth metals is briefly discussed in relation to characterization data.

Catalytic Cracking Behavior of n-Heptane over HZSM-5 Catalyst

The catalytic cracking of n-heptane, which was selected as a model compound for the paraffin of light straight-run naphtha, was studied over HZSM-5 catalyst in a fixed-bed microreactor. Its catalytic behavior was compared with that of 1-heptene and the effects of hydrothermal treatment and catalyst carrier were evaluated. The results showed that compared with the cracking of 1-heptene, the concentration of hydrogen, methane, and ethane was much higher in the cracked gas obtained from the cracking of n-heptane. We concluded that this mainly originated from the monomolecular cracking pathway while the content of propylene and butylene in liquefied petroleum gas (LPG) was much lower. Upon hydrothermal treatment, the total amount of acid decreased sharply, especially the strong Br[o]nsted acid (Bacid) sites, leading to a steep decline in catalytic activity. This was accompanied by the improved propylene/propane and butylene/butane molar ratios in the products. Meanwhile, the ratio between the C3 and C4 products decreased, suggesting a decrease in the occurrence of monomolecular cracking. The carrier also significantly influenced the cracking behavior of n-heptane. We found that the presence of Lewis acid (Lacid) sites in the carrier improved the n-heptane conversion and promoted the bimolecular cracking pathway. Generally, compared with the olefin reactant, paraffin usually shows much lower reactivity and light olefin selectivity and, therefore, it is not a desirable feed for the catalytic cracking reaction over the zeolite catalyst for the purpose of light olefin production.

Catalytic reforming of n-heptane on platinum-tungsten supported on gamma-alumina

The mono-metallic and bi-metallic catalysts have been prepared by impregnating with solutions containing a compound of H2PtCl6, WO3 and 1 ml HCl (0.1 mol). It should be noted that the catalysts’ activity and selectivity have been determined under these conditions: 450–500°C, and 15–25 atm by H2. For converting n-heptane, the molar ratio H2/C7H16 is 5, and LHSV is 1.5 ml/h. It has been proved that, under these experimental conditions, the conversion of n-heptane into branched aliphatic isomers is catalyzed by a bifunctional mechanism. The results indicate that in the presence of W, the catalysts have much higher selectivity and stability for isomerization reaction. At a given conversion, the bi-metallic catalysts produce much lower concentrations of cracked products. According to the tests, W modifies the support acidity resulting to the higher selectivity for isomerization and the lower one for cracking, and it also modifies the Pt properties.

Pt catalysts supported on β zeolite ion-exchanged with Cr(III) for hydroisomerization of n-heptane

A series of Pt catalysts supported on Hβ zeolite ion-exchanged with Cr(III) were prepared, characterized by ICP, XRD, BET, NH 3-TPD, H 2-TPR and H 2-chemisorption techniques, and evaluated in hydroisomerization of n-heptane with an atmospheric fixed-bed flow reactor. Pt catalyst supported on Hβ zeolite exhibits both lower selectivity to isomerized products and lower conversion of n-heptane than the counterparts supported on Cr(III)-exchanged Hβ zeolite. The optimal composition for Cr-bearing catalysts is 0.4 wt.% of Pt loading and 0.7 wt.% of Cr loading. This catalyst proves to be highly efficient in the hydroisomerization of n-heptane, giving a very high selectivity to isomerized products: 95.4% coupled with a high conversion of n-heptane: 72.1%. The substantial promotion effect of ion-exchanged Cr(III) species is discussed in relation to catalyst physicochemical properties.

Conversion of n-heptane to LPG and aromatics over Mo2C and W2C catalysts supported on ZSM-5

We have investigated the catalytic activity of W2C/HZSM-5 and Mo2C/HZSM-5 for conversion of n-heptane to LPG and aromatic products. The results show that the catalytic activity of the metallic carbides increases markedly in the presence of ZSM-5. For pure carbides, the main cracking products are methane and ethane as a result of the cleavage of the C–C bond at the end of the hydrocarbon chain. In contrast, the zeolitic catalysts produce LPG (propane, i-butane, and n-butane) through the cleavage of C–C bond in the medial bonds. It is observed that the metallic carbides play a key role in producing the aromatics, concerning the formation of olefin species and cyclization of them in the channels of zeolite.

Coking of Model Hydrocarbon Fuels under Supercritical Condition

Coking of three model compounds of hydrocarbon fuel—n-heptane, cyclohexane, and tricyclo[5.2.1.02.6]decane (JP-10)—during their thermal cracking processes under supercritical condition (873.15 K, 4.1 MPa) has been investigated. The product distributions of the thermal cracking are analyzed by gas chromatography−mass spectrometry (GC-MS). The morphology and microstructures of the cokes are characterized by the techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The results show that chemical structures play important roles in the thermal stability and coking property of the fuels. The thermal cracking conversion of n-heptane is highest, and the coke yield of JP-10 is highest under the same conditions. It is interestingly observed that the morphologies of the cokes produced from the thermal cracking of three fuels are quite different, which from n-heptane, cyclohexane, and JP-10 are in the forms of carbon nanofilaments, carbon nanotubes, and irregular carbon particles, respectively.

A Highly Efficient Hβ Zeolite Supported Pt Catalyst Promoted by Chromium for the Hydroisomerization of n-Heptane

Hβ zeolite supported Pt catalysts promoted by Cr, La, Ce, Al or Zn were prepared by the co-impregnation method, and characterized by XRD, BET, NH3-TPD and H2-TPR. Their catalytic activities were evaluated in the hydroisomerization of n-heptane with an atmospheric fixed-bed reactor. The Pt-bearing catalyst doped with Cr, La or Ce, especially Cr, is found to exhibit a much higher catalytic activity and isomerization selectivity than the catalyst without the dopant. At the low reaction temperature of 230 °C, the catalyst with a Pt loading of 0.4% and a molar ratio of Cr to Pt of 5:1 shows a high conversion of n-heptane of 77.1% coupled with a high selectivity to isomerization products of 94.4%. In contrast, over the counterpart catalyst without Cr, the conversion of n-heptane is 50.6% with a low selectivity to isomerization products of 82.4%. The substantial promotion effect of Cr is suggested to associate with the improved Pt dispersion, as well as the increased strong acid amount, due to the introducing of Cr into the catalyst.

Synthesis and activity measurement of the some bifunctional platinum loaded Beta zeolite catalysts for n-heptane hydroisomerization

In this study, two types of Beta zeolites having different Si/Al ratios (11.7 and 24.5) were synthesized hydrothermally using tetraethyl ammonium hydroxide (TEAOH) as a template. Different amounts of platinum (0.2%, 0.5% and 1.2%) were loaded on the protonated form of zeolite by incipient wet impregnation method applying hexachloroplatinic acid in 0.2N Cl − progressive ion solutions. Catalytic hydroisomerization reactions were carried out at atmospheric pressure in a fixed bed reactor with vertical placing and downward flow at three different temperatures, various WHSV (weight hourly space velocity) and n-H 2/ n-HC (molar hydrogen/hydrocarbon) ratio. Increase in Si/Al ratio in zeolites structures from 11.7 to 24.5 promoted selectivity and yield. It was found that optimum platinum content depends on the Si/Al ratio (zeolite acidity) in catalysts. Monobranched to dibranched isomers ratio were correlated with a linear function of n-heptane conversion. Such a correlation was found to be valid for various Si/Al ratios, metal content, processing temperature and pressure, WHSV and hydrogen to hydrocarbon ratio. This observation may indicate that in isomerization reactions, the monobranched isomers are first produced but subsequently transformed into multi-branched isomers.

SYNTHESIS AND DETERMINATION OF THE PROPERTIES OF THE BIFUNCTIONAL BETA ZEOLITE CATALYSTS FOR N-HEPTANE HYDROISOMERIZATION

ABSTRACT In this study, two types of beta zeolites with different Si/Al ratios (11.7 and 24.5) were synthesized hydrothermally using tetraethylammonium hydroxide (TEAOH) as the template. Different amounts of Platinum (0.2%, 0.5% and 1.2%) were loaded on the protonated form of zeolite by incipient wet impregnation method with hexachloroplatinic acid in 0.2N Cl - progressive ion solutions. Catalytic reactions were carried out at atmospheric pressure in a fixed bed reactor with vertical placing and downward flow at three different temperatures, various WHSV (weight hourly space velocity) and n-H 2 /n-HC (molar hydrogen / hydrocarbon) ratio (230, 250, 280 ˚C, 1.64, 2.48, 3.28 hr -1 and 6, 10, 14 respectively). Increasing the Si/Al ratio from 11.7 to 24.5 promoted the selectivity and yield. It was found that optimum platinum content depends on the Si/Al ratio (zeolite acidity) present in the zeolite catalyst. The monobranched to dibranched isomers ratio were correlated with a linear function of n-heptane conversion. Such a correlation was found to be valid for various Si/Al ratios, metal content, processing temperature and pressure, WHSV and hydrogen to hydrocarbon ratio. This observation may indicate that in isomerization reactions, the mono-branched isomers are first produced but subsequently transformed into multi-branched isomers.Keywords: Hydroisomerization , Beta zeolite , Bifunctional catalysts , n-Heptane

Hydroisomerization of n-heptane over bimetal-bearing H3PW12O40 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°C and WHSV of 1.4 h−1, 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%.

Naphtha reforming Pt-Re-Ge/γ-Al 2O 3 catalysts prepared by catalytic reduction : Influence of the pH of the Ge addition step

Pt-Re-Ge/γAl 2O 3 catalysts were prepared by the catalytic reduction method using different impregnation media (H 2O, HCl and NH 3) and different Ge contents (0.0, 0.1, 0.3, 1.0 and 2.0%). The influence of these preparation parameters on the activity for n-heptane conversion and the selectivity to toluene at atmospheric pressure was assessed. The catalysts were also characterized by ICP-AES, temperature programmed reduction, pyridine temperature programmed desorption and CO pulse chemisorption. The results show that as the pH is increased the Ge content increases and the catalysts present a lower hydrogenolytic activity and a lower toluene selectivity. Ge addition modifies both metal and acid functions. The catalyst with minimum Ge content prepared using water as impregnation medium has the best performance.

Mesoporous structure, surface acidity and catalytic properties of Pt/Zr–MCM-41 catalysts promoted with 12-tungstophosphoric acid

The influence of the Si/Zr molar ratio on the crystalline structure, textural properties, morphological features and surface acidity of Zr–MCM-41 mesoporous molecular sieves was investigated by X-ray diffraction (XRD), N 2 adsorption–desorption isotherms, 29Si MAS NMR, TEM and FTIR spectroscopy of pyridine adsorption techniques. It is found that the structural ordering of Zr–MCM-41 materials varies with the Si/Zr ratio, highly ordered mesoporous molecular sieves could be obtained for a Si/Zr ratio larger than 4. Calcination may significantly improve the structural regularity. After impregnation with 25 wt% of H 3PW 12O 40 (denoted as HWP hereafter), the surface Brönsted acidity of the Pt/Zr–MCM-41 samples was greatly enhanced by 4–8 times. In the hydroisomerization reaction of n-heptane, the n-heptane conversion over all the Pt/HPW/Zr–MCM-41 catalysts linearly increases with increasing the reaction temperature, while, the selectivity to isoheptanes gradually decreases. The molar ratio of multibranched to monobranched isoheptanes ( R) in the isomerization products varies within a very narrow range, between 0.8 and 1.2, which is several times greater than those reported in the literature at similar reaction conditions using zeolite-supported catalysts. The high R value obtained in this work is assumed to be related to the mesoporous geometry of the novel catalysts. In the products distribution, 2-methylhexane is predominant in the monobranched isoheptanes and 2,3-dimethylpentane is the prevailing compound being more than 50% of the multibranched isoheptane products. In the cracking products, butane (isobutane and n-butane) and propane are exclusively formed.