Simple Approach To Produce Diesel Distillate (C11−C28) from n

Energy & Fuels 2008, 22, 3605–3611

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Simple Approach To Produce Diesel Distillate (C11-C28) from n-Hexane under Mild Conditions Bo Wang,*,† Ying Yang,† Qingliang Ma,‡ and Hongzhu Ma† Institute of Energy Chemistry, School of Chemistry and Materials Science, Shaanxi Normal UniVersity, Xi’an 710062, People’s Republic of China, and Department of Applied Physics, College of Sciences, Taiyuan UniVersity of Technology, Taiyuan 030024, People’s Republic of China ReceiVed June 30, 2008. ReVised Manuscript ReceiVed August 15, 2008

A new convenient procedure has been carried out for the production of diesel distillates assisted by modified sulfated iron oxides under mild condition (298 K and 1.01 MPa). The products successfully obtained by this method are mainly long, linear hydrocarbons from C13 to C24, all of which can be used as diesel distillates. Correlation of the catalytic performance to the structural properties is also discussed by a Fourier transformation infrared spectrometer (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the addition of a different modifier to sulfated iron oxide can affect the performance of catalysts and may be due to the different strength of acid, dispersibility, crystallization degree, crystal particles, and ratio of deprotonated and protonated S element. In comparison to the reaction processed in the high temperature and high pressure, this process became rather easy with a simple operation, lower energy consumption, and environmentally friendly.

1. Introduction Because we live in a world powered by fossil fuels, the dependence on oil has made energy a vital component of our everyday needs. Diesel engines dominate the field of commercial transportation and agricultural machinery because of its excellent fuel efficiency. The consumption of diesel fuel is several times higher than that of gasoline. Because of the shortage of petroleum products and its increasing cost, it has prompted everyone to take a careful look at the issues dealing with our diesel fuel supply and effective use.1 As a specific fuel, diesel fuel is a blend of petroleum-derived compounds called middle distillates, heavier than gasoline but lighter than lubricating oil. It consists mostly of hydrocarbons ranging from 10 to 28 carbons, whose boiling points are between about 150 and 400 °C. Cetane number (CN), depending upon the chemical composition of diesel fuel, is one of the most significant properties to specify the ignition quality of diesel fuel. Generally speaking, normal paraffins have higher CNs that increase with molecular weight, but isoparaffins have lower CNs than n-paraffins at the same carbon number. Isomers with several short side chains have lower CNs than those with a long side chain.2-5 In recent years, the research focused on the synthesis of long-chain normal paraffins from short-chain alkanes has been reported. The high-temperature Fischer-Tropsch synthesis * To whom correspondence should be addressed. Telephone: +86-2985308442. Fax: +86-29-85307774. E-mail: [email protected]. † Shaanxi Normal University. ‡ Taiyuan University of Technology. (1) Kamat, P. V. J. Phys. Chem. C 2007, 111, 2834–2860. (2) Santana, R. C.; Do, P. T.; Santikunaporn, M.; Alvarez, W. E.; Taylor, J. D.; Sughrue, E. L.; Resasco, D. E. Fuel 2006, 85, 643–656. (3) Ramadhasa, A. S.; Jayaraja, S.; Muraleedharana, C.; Padmakumarib, K. Energy 2006, 31, 2524–2533. (4) Lu, X. C.; Yang, J. G.; Zhang, W. G.; Huang, Z. Energ Fuel 2005, 19, 1879–1888. (5) Ijam, M. J.; Abu-Elgheit, M. A.; Fahim, M. A. Ind. Eng. Chem. Prod. Res. DeV. 1981, 20, 752–755.

(FTS) process is considered as an effective process in producing a wide range of liquid hydrocarbon fuels, such as diesel oil from CO and H2. The FTS products are almost normal paraffins, and the product selectivity follows the Anderson-Schulz-Flory (ASF) distribution.6 Martı´nez reported FTS of hydrocarbons over mesoporous Co/SBA-15 catalysts at the temperature of 498 K; the selectivity of hydrocarbons is 95.6%.7 Ravishankar investigated that MCM-22 molecular sieve as supports of cobalt catalysts in the FTS with high selectivity of long-chain hydrocarbons (C5+).8 Catalytic oxidation of methane is also an important path for synthesis long-chain hydrocarbons. Amariglio reported the coupling of methane homologation to C7-C8 in 570 K with a two-step procedure by using metal catalysts.9 Wan investigated oxidative dehydrogenation of ethane over BaFdoped tetragonal LaOF catalysts at 898 K.10 Most of them required high temperature to maintain an adequate activity, while others need high pressure.11 Hence, they are not cost-effective. It is necessary to search a facile method for synthesis of longchain normal paraffins that can be carried out under mild conditions. As one of the gasoline components and an important hydrocarbon, n-hexane has a moderate carbon atom number and abundant resource, and it is seldom reported that short-chain n-alkane converted directly to long-chain hydrocarbon under mild conditions. Therefore, oxidative coupling of n-hexane directly to long-chain hydrocarbon at room temperature and air pressure has been chosen as the objective reaction. (6) Tavakoli, A.; Sohrabi, M.; Kargari, A. Chem. Eng. J. 2008, 136, 358–363. (7) Martı´nez, A.; Lo´pez, C.; Ma´rquez, F.; Dı´az, I. J. Catal. 2003, 220, 486–499. (8) Raman, R.; Mianhui, M. L.; Armando, B. A. Catal. Today 2005, 106, 149–153. (9) Amariglio, H.; Pareja, P.; Amariglio, A. Catal. Today 1995, 25, 113– 125. (10) Wang, H. L.; Chao, Z.; Weng, W.; Zhou, X.; Cai, J. X.; Tsai, K. Catal. Today 1996, 30, 67–76. (11) Chou, L.; Cai, Y.; Zhao, B.; Yang, J.; Zhao, J.; Niu, J.; Li, S. Stud. Surf. Sci. Catal. 2004, 147, 619–624.

10.1021/ef800521j CCC: $40.75  2008 American Chemical Society Published on Web 09/27/2008

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Recently, many scholars are fascinated by solid acid catalysis, because of some additional advantages of catalyst, such as easier separation from the reaction mixture, no corrosion to the reactor, and free from pollution, etc. Therefore, they are worthy of attention in theoretical research and synthetic application.12,13 Owing to these characteristics, heterogeneous solid acid catalysts are emerging as very attractive alternatives to the conventional homogeneous acidic reagents. According to a recent review of industrial acid-base catalysis of the 127 processes identified, over 115 are solid-acid-catalyzed.14,15 It clearly indicates the significance of those materials and the scope of their commercial exploitation. Among various solid acid catalysts, the sulfated metal oxides (SO42-/MxOy) based on iron oxide have emerged as powerful catalysts for their high acidity, nontoxicity, and high activity at low temperatures. Additionally, the activity, selectivity, and stability of sulfated metal oxide catalysts were also improved by the addition of noble metals and transition-metal oxides, such as Pt and Co. Because of so many advantages, they have been widely used in many large volume applications, especially in the petroleum industry for alkylation and isomerization reactions.16,17 Nowadays, studies focused on the synthesis of long-chain hydrocarbon have evoked so many interests. Therefore, the aim of our work is to propose a simple and effective method to synthesize diesel fuel distillation from lowmolecular-weight alkane under mild conditions. To obtain satisfactory results, the flow air and slurry reactor were chosen in this paper. First, catalytic oxidation of hydrocarbons by air or oxygen is one of the significant reactions in the chemical and petrochemical industries. Their function is to upgrade naphthas to motor fuel blending, whose components are derived from catalytically promoting specific groups of chemical reactions. A study by Hill on a few oxidizing systems based on transition-metal complexes as catalysts also indicated that oxygenations are distinguished significantly in their efficiencies and selectivity.18 Second, two types of reactors are widely employed in industries: the fixed-bed reactor and the slurry bubble column reactor. Sie and Krishna have compared the advantages and disadvantages of both reactors.19,20 The major drawbacks of the slurry reactor are the dependence on continuous separation between catalyst and liquid products, a smaller scale factor compared to the fixed-bed reactor, and possible attrition of catalyst particles. The advantages are (i) low pressure drop in the reactor, (ii) excellent heat-transfer characteristics resulting in stable reactor temperatures, (iii) no diffusion limitations, (iv) possibility of continuous refreshment of catalyst particles, (v) and powdered catalysts can suspend well in the fluid. Therefore, the slurry reactor was chosen in this reaction. As mentioned above, we herein report the preparation of SO42-/Fe2O3-MxOy (M ) Mo, Sb, and Zn) and its application on the coupling of n-hexane in the simulative slurry reactor in the presence of flow air under mild conditions (293-298 K and (12) Reddy, B. M.; Sreekanth, P. M.; Lakshmanan, P.; Khan, A. J. Mol. Catal. A: Chem. 2006, 244, 1–7. (13) Reddy, B. M.; Sreekanth, P. M.; Yamada, Y.; Kobayashi, T. J. Mol. Catal. A: Chem. 2005, 227, 81–89. (14) Reddy, B. M.; Sreekanth, P. M.; Lakshmanan, P. J. Mol. Catal. A: Chem. 2005, 237, 93–100. (15) Hattori, H. Chem. ReV. 1995, 95, 537–558. (16) Hino, M.; Arata, K. Appl. Catal., A 1998, 173, 121–124. (17) Matsuhashi, H.; Miyazaki, H.; Kawamura, Y.; Nakamura, H.; Arata, K. Chem. Mater. 2001, 13, 3038–3042. (18) Hill, C. L.; Delannoy, L.; Duncan, D. C.; Weinstock, I. A.; Renneke, R. F.; Reiner, R. S.; Atalla, R. H.; Han, J. W.; Hillesheim, D. A.; Cao, R.; Anderson, T. M.; Okun, N. M.; Musaev, D. G.; Geletii, Y. V. C. R. Chimie 2007, 10, 305–312. (19) Sie, S. T.; Krishna, R. Appl. Catal., A 1999, 186, 55–70. (20) Krishna, R.; Sie, S. T. Fuel Process. Technol. 2000, 64, 73–105.

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1.01 MPa). The products were analyzed by an ultraviolet (UV) spectrophotometer and gas chromatography-mass spectrometry (GC-MS). Correlation of the catalytic performance to the structural properties is also discussed on the basis of various characterizations, such as a Fourier transformation infrared spectrometer (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). 2. Experimental Section 2.1. Preparation of SO42-/Fe2O3-10% MxOy Catalysts. All chemical reagents used in the experiment were analytical-grade and without any further purification. The preparation of binary oxides is described below. First, a certain amount of Fe(OH)3 and MoO3 is mixed according to the appropriate ratio (9:1), and then the powder was grinded repeatedly using an agate mortar. Second, sulfation of this mixture was performed by percolating 200 mL of 1.0 mol/L H2SO4 solution. After that, remove the air was removed and immerged for 12 h. Finally, annealing was carried out at 823 K for 3 h to obtain the final catalysts SFeMo. The catalyst SFeSb and SFeZn were prepared by the same method. All of the catalysts were stored in a sealed ampule for standby. To obtain a clean surface, the catalysts were pretreated at 823 K for 1 h in a nitrogen atmosphere before each term. 2.2. Characterization of the Catalyst. The different samples were degassed at 373 K for 2 h under high vacuum followed by monitoring on a Fourier transform infrared spectrophotometer Eouinx55 (Germany) equipped with a MCT detector (resolution of 4 cm-1) in the range of 400-4000 cm-1. The samples were prepared as self-supporting wafers (2 cm in diameter and typically 7-8 mg/cm2), placed inside a cell. The powder diffraction patterns were recorded on a X-ray powder diffractometer (XRD) PW 150 (Philips), using Ni-filtered Cu KR radiation (λ ) 1.5406 Å) at 40 kV, 30 mA, and a scanning range 2θ of 10-70°. Crystalline phases were identified with the help of Joint Committee on Powder Diffraction Standards (JCPDS) data files. The crystallite size (in nanometers) was calculated from the broadening of the strongest peak of Fe2O3, peak (220) at 2θ ) 33.15, using the Debye-Scherrer equation

D)

Kλ β cos θ

where k is the crystallite shape constant (k ≈ 1), λ is the radiation wavelength (Å), β is the line breadth (radians), and θ is the Bragg angle. The surface composition of the catalyst was analyzed by XPS using a XSAM800 (Kratos) equipment operated in FAT mode with non-monochromatic Mg X-radiation. The base pressure in the chamber was in the range of 10-8 Pa. Charging of the catalyst sample was corrected by setting the binding energy of adventitious carbon (C1s) at 284.6 eV. The samples were outgassed in a vacuum oven overnight before XPS measurements. 2.3. Reaction Procedure. Figure 1 showed the schematic diagram of the SBCRs for the catalytic oxidative coupling of n-hexane. The catalytic reaction was carried out in a slurry reactor under mild conditions (293-298 K and 1.01 MP) using an undivided cell of 0.5 L capacity. The reaction cell was cooled by the fluxion water to keep the reaction in the constant temperature. A total of 5 g of catalysts was packed in 100 mL of n-hexane, and the rate of the gas and liquid mixture was 5:1 (vol ratio). The whole reaction was experimented by passing the air with continuous flows adjusted by mass flow controllers; the total volumetric flow rate of air was 400-500 mL/min. Products were analyzed by UV spectra and GC-MS. 2.4. Analysis of the GC-MS. The composition and relatively selectivity of the products was analyzed by GC-MS (Shimadzu GC-2010 gas chromatograph coupled with a Shimadzu QP2010 mass spectrometer, Japan). The gas chromatograph was fitted with a fused silica capillary column OV-1 (30 × 0.25 mm inner diameter and 0.25 µm coating). The following oven was programmed from

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Figure 1. Schematic setup for the experiment.

the initial temperature of 35 °C and increased at the rate of 10 °C/min to the final temperature of 260 °C, which was maintained for 15 min. The carrier gas was helium at a constant flow of 1 mL/min. The splitting ratio was 20:1. Electron impact mass spectra were taken at 70 eV and scan at 0.2 scans/s from m/z 30 to 500 amu. The library searches and spectral matching of the resolved pure components were conducted on the National Institute of Standard and Technology (NIST) 127 MS database. The identification of each peak was performed by comparing the retention time (Rt) and mass spectrum of the compounds to that of the authentic reference substances.

3. Results and Discussion 3.1. Characterization of the Catalysts. 3.1.1. Infrared Spectroscopy. The SdO structure was significant for generation of active sites on sulfate-promoted oxide samples.21 The strong ability of SdO in sulfate complexes to accommodate electrons from basic molecules was a driving force for generation of highly active properties.22 The acidic properties generated by the inductive effect of SdO bonds of the complex were strongly affected by the environment of sulfate ion. Thus, it can be proposed that catalytic properties would be modified by the type of SdO in sulfate complex, especially the coverage of sulfate species on the catalyst surface.23 Therefore, a well-defined S feature must be analyzed for catalytic activity. The different catalyst samples, which were dried in vacuo at 373 K for 1 h first, were diluted in KBr. The infrared absorption spectra displayed in Figure 2. Generally, a wide band appeared at 1632 cm-1 corresponding to the flexion vibration band of the H2O molecule, which was ascribed to the physisorbed water in the surface of the catalyst. The peaks between 800 and 1450 cm-1 were the characteristic peaks assigned to the SdO or S-O bond, and the structure of the solid catalysts remained stable even when many other components were promoted.24-26 As was expected, a large difference was confirmed among these catalysts. The SFeMo had five absorption bands. A band (21) Jung, S. M.; Grange, P. Catal. Today 2000, 59, 305–312. (22) Comelli, R. A.; Vera, C. R.; Parera, J. M. J. Catal. 1995, 151, 96–101. (23) Martınez, L. M.; Montesdecorrea, T. C.; Odriozola, J. A.; Centeno, M. A. Catal. Today 2005, 107, 800–808. (24) Shaffer, G. W.; Doerr, A. B.; Purzycki, K. L. J. Org. Chem. 1972, 37, 25–29. (25) Partenheimer, W. Catal. Today 1995, 23, 69–158. (26) Salas, P.; Hernhndez, J. G.; Montoya, J. A.; Navarrete, J.; Salmones, J.; Schifter, I. J. Mol. Catal. A: Chem. 1997, 123, 149–154.

Figure 2. Representative infrared spectrum of catalysts (1) SFeMo, (2) SFeSb, and (3) SFeZn.

located at 867 cm-1 was assigned to the S-O symmetric stretching. A result that the S-O asymmetric stretching splits into three peaks at 990, 1096, and 1206 cm-1 suggests that symmetry is lowered. In other words, the surface SOx (SO4) species exist as bidentate complexes strongly bonded with metal oxides. Furthermore, the bands centered in 1415 cm-1 correspond to the asymmetric SdO stretching vibrations observed, which could induce the acidity of the catalyst and improve its catalytic activity. It should be pointed out that the acidity of the catalyst strengthens as the band of 1415 cm-1 extends in height as follow: SFeMo > SFeSb > SFeZn. This is responsible for an enhancement of the Lewis acidity on metal oxides. From the present IR spectra, the binding mode of metalpromoted sulfated iron oxide maybe as follows (Figure 3), although several structures have been proposed. The MxOy coordinated to SdO groups acts as electron-withdrawing species followed by the inductive effect illustrated by the arrows; thus, the Lewis acid strength of Fe3+ becomes stronger. The Lewis acid sites can easily convert to Brønsted acid points in the

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Figure 3. Surface mode of SFeM.

Figure 4. X-ray powder diffraction of catalysts (1) SFeMo, (2) SFeSb, and (3) SFeZn. Table 1. Some Parameters Obtained from XRD Analysis sample name

I(220) peak

fwhm

crystallite size (nm)

SFeMo SFeSb SFeZn

897 1022 1184

0.172 0.164 0.154

593 637 707

presence of water. Therefore, the catalysts can act both as a Lewis acid and Brønsted acid in the catalytic reaction. 3.1.2. X-ray Powder Diffraction. It is obvious that only one phase can be observed in SFeMo from Figure 4 (1). The pattern is characteristic of the Fe2O3 phase with rhombohedral structure, with the representative 2θ at 33.15°, 35.61°, and 54.09° according to JCPDS 33-0664. No other new compounds was detected, indicating that the apparent dispersion of MoO3 was kept on the surface, which is in favor of improving the activity of the catalyst. However, the different diffraction feature displayed in SFeSb and SFeZn are shown in (2) and (3) of Figure 4. Apart from the signals of Fe2O3, the weak signals in SFeSb at 2θ ) 27.21°, 35.01°, and 53.25° can be assigned to the squawcreekite FeSbO4 (JCPDS 34-0372), with the formation of this structure possibly as a result of the fact that a small amount of Sb2O3 has been transformed into FeSbO4 after annealing. The involved reactions are 2Sb2O3 + O2 ) 2Sb2O4 2Fe2O3 + 2Sb2O4 + O2 ) 4FeSbO4 The detection of ZnO accounts for its weaker dispersed ability of SFeZn than SFeMo and SFeZn. According to the DebyeScherrer equation calculation shown in Table 1, it can also be indicated that the crystallite size based on the peak of the 220

plane gradually increased with different modifiers (MoO3 < Sb2O3 < ZnO). It can also be seen that the crystallinity degree of SFeMo is lower than SFeSb and SFeZn. After the reaction, all of the catalysts were also investigated by X-ray powder diffraction. Almost the same result obtained. It can be concluded that the crystalline phases of the catalyst were very stable during the reaction. 3.1.3. X-ray Photoelectron Spectroscopy. XPS responses of all of the samples can be assigned to the elements Fe, M (Mo, Sb, and Zn), O, and C, and no other elements have been detected. The typical XPS spectra of S2p3/2 after exposure to hexane are shown in Figure 5. It can be seen that the binding energy of S2p3/2 was around 169 eV, which was the same as S2p3/2 in SO42-. Hence, it can be concluded that the element sulfur exists in the form of the six-oxidation state (S6+), which resulting in the remarkable acidity on the surface of catalysts. This is also consistent with the results of FTIR. Additionally, the peak corresponding to sulfate species exhibits a pronounced asymmetry. Decomposition of this peak by Gaussian function leads to two components. Correlation of the evolution of the XPS spectra as a function of sulfur content with other data obtained from FTIR of the same catalysts led to an assumption that the band located at 169 eV could be associated with deprotonated sulfate species, whereas that located at 170 eV could be associated with protonated ones. According to the peak area ratio of S169/170 indicated in Table 2, it is obvious that there is a tendency to shift to the higher energy with the order of SFeMo > SFeSb > SFeZn. An increase in the population of the protonated species occurs after exposure to hexane organic molecules. This could be a consequence of a more advanced interaction of sulfate groups with the iron oxide support. At the same time, the peak at 160.3 eV after the reaction shows the state of S2-, indicating the reduction part of the SO42- during the reaction. To understand the chemical state of carbon during the reaction, the Gaussian simulation curve of carbon was drawn to analyze their valence distribution. It can be seen from the XPS spectra shown in Figure 6 that the C1s peak in the sulfated catalyst deconvoluted into four peaks, which represented four kinds of chemistry environment based on the principle and instrument handbook of XPS. The largest peak at BE ∼ 284.8 eV may have corresponded to saturated hydrocarbonaceous deposits, and that at 285.5 eV may have corresponded to unsaturated hydrocarbon deposits. Apart from two main carbon components, oxidized carbon components were also present. The smaller separate peak appearing at 288.8 eV indicated heavily oxidized residues (COOH groups). Just a qualitative viewing of the C1s peak convincingly demonstrates that the overwhelming majority of carbon must have belonged to saturated hydrocarbonaceous entities. Although the carbon content of three various samples were rather different, the distribution of C1s components was qualitatively similar. The other elements, such as Fe, Mo, Sb, and Zn, were also investigated before and after the reaction. No changes of the

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Energy & Fuels, Vol. 22, No. 6, 2008 3609

Figure 5. Typical XPS spectra of S2p3/2 (SFeMo as the catalyst). Table 2. XPS Parameters of the Investigated Catalystsa S169/170 SO42-/Fe2O3-MoO3 SO42-/Fe2O3-Sb2O5 SO42-/Fe2O3-ZnO a

fresh catalysts

exposed to hexane

1.84 2.97 3.85

1.17 1.35 1.72

Data were recorded after catalysts exposure to hexane for 1 h.

Figure 7. UV spectrum of liquid products (SFeMo as the catalyst).

Figure 6. Valence curve fit of C1s in SFeMo after the reaction.

valence was found, indicating that these elements were stable during the reaction. 3.2. Analysis of Products. 3.2.1. UV Spectrum. It is wellknown that the UV spectrum is very sensitive to the unsaturated compound. Therefore, the time effect on the catalytic reaction assisted by the SFeM (Mo, Sb, and Zn) catalyst was detected by UV-vis spectra in the range of 400-200 nm, which was used to investigate the whole process of the reaction. It can be seen from Figure 7, with the time prolong, that three obvious peaks were observed at 205, 226, and 258 nm and descended gradually. The K absorption band (205 nm) caused the shoulder to move to a lower energy slightly, which was due to the substituent effect in the electronic spectra of aromatic conjugated systems. The energy needed by the band of π-π* transition reduced; therefore, the K absorption generated a bathochromic. The B adsorption band, characteristic peak of the hypsochromic benzene ring shifted from 261 to 271 nm, indicating the formation of the aromatic compound. The evolution of the weak intensity of the peak shows that the concentration of the benzene ring was very small during the reaction. Although precise molecular structure information cannot be extracted from these

electronic absorption spectra, the results are qualitatively in accordance with GC-MS results. 3.2.2. GC-MS. The combination of gas chromatography and mass spectrometry is more suited for detection and identification of volatile organic compounds. It provides a simple method for qualitative and quantitative analysis of target components and has been known for its superior separation, greater sensitivity, and shorter measuring time.27 Figure 8 shows the total ion chromatogram (TIC) of the products with SFeMo as the catalyst (the peak of the reactant was taken off). Each peak was identified by comparing with Rt and mass spectra obtained for the standard compound. According to the analysis of the GC-MS exhibited in Figure 8 and Table 3, it can be inferred that the main products were linear hydrocarbon from C11 to C24, with the total selectivity approximately 83.85 wt %. A small quantity of oxygenous compounds and aromatic hydrocarbon were also observed during the reaction. This result was also proven by the UV-vis spectrum. As expected, the main products were linear hydrocarbons in the range of C10-C28, and all of them can be used as diesel fuel components, indicating that SFeMo is a promising catalyst for converting n-hexane to middle distillate fuels under (27) Giumanini, A. G.; Verardo, G. Ind. Eng. Chem. Res. 2001, 40, 1449–1453.

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Figure 8. GC-MS spectrum of the products (SFeMo as the catalyst). MS data: 70 eV, m/e (relative intensity) C14, tetradecane, 29 (18), 39 (6), 43 (69), 55 (15), 67 (2), 71 (55), 84 (8), 85 (43), 99 (10), 113 (6), 127 (4), 155 (2), 198 (6); C15, pentadecane, 29 (25), 39 (6), 43 (76), 55 (20), 67 (2), 71 (57), 84 (6), 85 (38), 99 (10), 113 (5), 127 (3), 141 (2), 155 (1), 169 (1), 212 (2); C16, hexadecane, 29 (23), 39 (5), 43 (73), 55 (21), 67 (2), 71 (54), 84 (6), 85 (38), 96 (1), 99 (11), 113 (6), 127 (4), 141 (2), 169 (1); C17, heptadecane, 29 (21), 39 (4), 43 (70), 55 (21), 57 (100), 67 (2), 71 (60), 83 (6), 85 (42), 96 (1), 99 (13), 113 (7), 127 (5), 141 (3), 155 (2), 169 (1); C18, octadecane, 29 (19), 39 (4), 43 (67), 55 (22), 57 (100), 67 (2), 71 (62), 84 (7), 85 (46), 96 (1), 99 (16), 113 (10), 127 (6), 141 (4), 155 (3), 169 (2), 183 (2), 197 (2), 211 (1), 254 (4); C19, nonadecane, 29 (17), 39 (3), 43 (68), 55 (22), 57 (100), 67 (3), 71 (60), 83 (7), 85 (43), 99 (16), 113 (10), 141 (4), 155 (3), 169 (2); C20, icosane, 29 (17), 39 (4), 43 (63), 55 (22), 57 (100), 67 (2), 71 (60), 85 (47), 96 (2), 99 (17), 113 (12), 127 (8), 141 (5), 149 (36), 150 (4), 155 (4), 169 (3); C21, henicoscane, 29 (12), 39 (3), 43 (60), 55 (19), 57 (100), 67 (3), 71 (70), 83 (9), 86 (4), 96 (2), 99 (19), 127 (8), 141 (5), 155 (4), 169 (3), 197 (2); C22, docosane, 27 (10), 41 (25), 43 (60), 57 (100), 71 (80), 85 (55), 99 (25), 113 (20), 127 (18), 141 (16), 155 (16), 169 (15), 183 (3.0), 197 (2.5), 211 (2.5); C23, tricosane, 27 (9), 41 (22), 43 (62), 57 (100), 71 (78), 85 (50), 99 (20), 113 (18), 127 (20), 141 (25), 155 (8), 169 (8), 183 (6), 197 (5), 211 (2), 225 (2); C24, tetracosane, 27 (11), 41 (25), 43 (60), 57 (100), 71 (75), 85 (55), 99 (20), 113 (20), 127 (16), 141 (15), 155 (9), 169 (8), 183 (6), 197 (3), 211 (2), 225 (2.5), 239 (2), 253 (1), 296 (5). Table 3. Conversion of Hexane over SO42-/Fe2O3-MxOy Catalystsa linear HC relative selectivity (wt %)

a

number

compound

retention time (min)

SFeMo

SFeSb

SFeZn

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

dimethyl-hexane toluene undecane dodecanal tetradecane 2,6,11-trimethyl-dodecane pentadecane 1-pentadecene hexadecane heptadecane 3-dodecylcyclohexanone octadecane nonadecane icosane henicoscane cyclohexyl tridecyl oxalate dibutyl phthalate docosane tricosane tetracosane total selectivity of liner HC (%) conversion of hexane (%)

2.81 3.83 7.69 7.98 9.37 9.72 10.10 10.50 10.78 11.41 11.70 12.01 13.13 14.27 15.20 15.56 15.95 16.43 16.74 18.31