Hydrodesulfurization of Fluidized Catalytic Cracking Diesel Oil over

Jul 2, 2009 - The addition of MB made the WS2 slabs grow larger and the stacking degree become higher. The addition of MB also enhanced the overall ac...
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3846

Energy & Fuels 2009, 23, 3846–3852

Hydrodesulfurization of Fluidized Catalytic Cracking Diesel Oil over NiW/AMB Catalysts Containing H-Type β-Zeolite in Situ Synthesized from Kaolin Material Guofu Wan,† Aijun Duan,*,† Ying Zhang,‡ Zhen Zhao,*,† Guiyuan Jiang,† Dengqian Zhang,† Zhenyong Gao,† Jian Liu,† and Keng H. Chung§ State Key Laboratory of HeaVy Oil Processing and Department of Materials Science and Engineering, China UniVersity of Petroleum, Beijing, 102249, P. R. China, and Well Resources Inc., 3919-149A Street, Edmonton, Alberta, Canada T6R 1J8 ReceiVed March 1, 2009. ReVised Manuscript ReceiVed June 7, 2009

A series of hydrodesulfurization (HDS) catalysts of Ni-W supported on γ-Al2O3-MB (denoted as AMB) composites with various amounts of H-type β zeolite (denoted as MB) synthesized from kaolin were prepared. The samples were characterized by means of N2 physisorption, XRD, SEM, TPR, HRTEM, XPS, and FT-IR spectroscopy of pyridine adsorption. The characterization results showed that, compared with NiW/Al2O3, the addition of MB reduced the interaction between W and the support. The addition of MB made the WS2 slabs grow larger and the stacking degree become higher. The addition of MB also enhanced the overall acidity of AMB supports and led to an increase in the ratio of Bro¨nsted acid of the NiW catalysts. W exhibited higher sulfidation extent in MB-containing NiW/AMB3 catalyst than that in NiW/Al2O3. The fluidized catalytic cracking (FCC) diesel HDS activity changed with the addition of varying amounts of MB on NiW/AMBi catalysts. The optimal MB content was 32 wt % in composite AMB support. A higher deep HDS efficiency was achieved on NiW/AMB3 than that of traditional NiW/Al2O3. Higher HDS activity of NiW/AMB3 was attributed to the appropriate ratio of Bro¨nsted acid to Lewis acid and/or the enhanced hydrogenation activity. For NiW/AMB3 catalyst, the effect of operation conditions on the degree of HDS of FCC diesel was investigated. The ultradeep desulfurization of FCC diesel oil, in which the sulfur content is below 10 ppm, could be obtained under the optimal operation conditions: T ) 360 °C, P ) 5 MPa, LHSV ) 1 h-1, and H2/oil ) 600.

1. Introduction Due to the environmental restrictions, the limit of sulfur content is an important factor in the regulation of gasoline and diesel fuels and the sulfur content is expected to be lowered to 10-50 ppm level in the most of developed countries and developing countries by the end of this decade.1,2 Hydrodesulfurization (HDS) process is one of the effective processes of choice for removing sulfur from gasoline and diesel. The refractive sulfur species are dibenzothiophene (DBT) and its alkyl-substituted derivatives such as 4,6-substitued dibenzothiophenes (DBTs),1,3,4 due to the steric hindrance of substituted groups in the 4,6-position of DBT molecules. Hydrodesulfurization of dibenzothiophene (DBT) or 4,6-DMDBT is known to undergo two parallel pathways: direct desulfurization (DDS) by cleavage of the C-S bond and hydrogenation * Corresponding author. Tel: (+8610) 89731586. Fax: (+8610) 69724721. E-mail: [email protected] (A.D.), [email protected] (Z.Z.). † State Key Laboratory of Heavy Oil Processing, China University of Petroleum. ‡ Department of Materials Science and Engineering, China University of Petroleum. § Well Resources Inc. (1) Song, C. Catal. Today 2003, 86, 211–263. (2) Babich, I. V.; Moulijn, J. A. Fuel 2003, 82, 607–631. (3) Song, C.; Ma, X. Appl. Catal., B 2003, 41, 207–238. (4) Bataille, F.; Lemberton, J. L.; Michaud, P.; Pe´rot, G.; Vrinat, M.; Lemaire, M.; Schulz, E.; Breysse, M.; Kasztelan, S. J. Catal. 2000, 191, 409–422.

(HYD).5-13 Several approaches were proposed in order to improve catalytic performance for the HDS of 4,6-DMDBT.1,3,14-25 (5) Lamure-Meille, V.; Schulz, E.; Lemaire, M.; Vrinat, M. Appl. Catal., A 1995, 131, 143–157. (6) Olguin Orozco, E.; Vrinat, M. Appl. Catal., A 1998, 170, 195–206. (7) Meille, V.; Schulz, E.; Lemaire, M.; Vrinat, M. J. Catal. 1997, 170, 29–36. (8) Macaud, M.; Milenkovic, A.; Schulz, E.; Lemaire, M.; Vrinat, M. J. Catal. 2000, 193, 255–263. (9) Yang, H.; Fairbridge, C.; Chen, J.; Ring, Z. Catal. Lett. 2004, 97, 217–222. (10) Zuo, D.; Li, D.; Nie, H.; Shi, Y.; Lacroix, M.; Vrinat, M. J. Mol. Catal. A: Chem. 2004, 211, 179–189. (11) Rabarihoela-Rakotovao, V.; Brunet, S.; Berhault, G.; Pe´rot, G.; Diehl, F. Appl. Catal., A 2004, 267, 17–25. (12) Egorova, M.; Prins, R. J. Catal. 2004, 224, 278–287. (13) Rabarihoela-Rakotovao, V.; Brunet, S.; Pe´rot, G.; Diehl, F. Appl. Catal., A 2006, 306, 34–44. (14) Isoda, T.; Nagao, S.; Ma, X. L.; Korai, Y.; Mochida, I. Energy Fuels 1996, 10, 1078–1082. (15) Pe´rot, G. Catal. Today 2003, 86, 111–128. (16) Yoosuk, B.; Kim, H.; Song, C. Catal. Today 2008, 130, 14–23. (17) Kwak, C.; Joon Lee, J.; Sang Bae, J.; Choi, K.; Heup Moon, S. Appl. Catal., A 2000, 200, 233–242. (18) Landau, M. V.; Berger, D.; Herskowitz, M. J. Catal. 1996, 159, 236–245. (19) Bataille, F.; Lemberton, J. L.; Pe´rot, G.; Leyrit, P.; Cseri, T.; Marchal, N.; Kasztelan, S. Appl. Catal., A 2001, 220, 191–205. (20) Cid, R.; Neira, J.; Godoy, J.; Palacios, J. M.; Lo´pez Agudo, A. Appl. Catal., A 1995, 125, 169–183. (21) Li, D.; Nishijima, A.; Morris, D. E. J. Catal. 1999, 182, 339–346. (22) Kunisada, N.; Choi, K.; Korai, Y.; Mochida, I.; Nakano, K. Appl. Catal., A 2004, 276, 51–59. (23) Lecrenay, E.; Sakanishi, K.; Mochida, I. Catal. Today 1997, 39, 13–20.

10.1021/ef900178n CCC: $40.75  2009 American Chemical Society Published on Web 07/02/2009

Hydrodesulfurization of FCC Diesel Oil

The addition of zeolites appreciably improves hydrodenitrogenation and hydrodearomatization activities of the catalysts, which is desirable in diesel hydrotreating. The addition of acidic component of zeolites in catalysts can promote the hydroisomerization and dealkylation activities of a catalyst.14,19 Yumoto et al.26 reported that the addition less than 10% of zeolite in CoMo/Al2O3 catalyst increased the HDS activity by 40% compared with the conventional CoMo/Al2O3 catalyst on a straight run gas oil with 1.38 wt % sulfur. They attributed the increase in HDS activity to the increasing of hydrogenation rate by the acidity from the zeolite and the easier adsorption of DBT ring with the electronic effect from the proton of zeolite. Kunisada et al.27 reported that an alumina-zeolite-supported NiMo catalyst had a high HDS activity for refractory sulfur species even at 1.67% H2S in H2. Furthermore, zeolitecontaining support helped to enhance the release of sulfur species from the active sites. Landau et al.18 reported that CoMo on alumina-containing HY zeolite was three times more active than the commercial CoMo/Al2O3 catalyst in HDS of 4,6DMDBT. They attributed it to the demethylation of benzenic rings and the cleavage of the C-C bond connecting the two benzenic rings, due to a direct action of the catalyst acidity. Zeolite Y is one of the most extensively studied zeolites for HDS catalyst support, due to its appropriate pore structure, acidity, and thermal and hydrothermal stabilities. Zeolite β is a large-pore zeolite similar to zeolite Y, which has a high SiO2/ Al2O3 ratio than zeolite Y. Compared with zeolite Y, zeolite β has a higher hydroisomerization activity, lower hydrogentransfer capacity, and lower catalyst deactivation.28,29 These characteristics make zeolite β a good candidate as HDS catalyst support for removing refractory sulfur species and reducing catalyst deactivation. The large pore-zeolite β is also beneficial to catalytic hydrocracking function. However, most studies about the application of the zeolite β or Y are mainly focused on the hydrocracking of heavy oil. Only few works have been done on HDS, especially on the hydrotreating performance of real inferior diesel distillations using zeolite β as acidic components of the catalyst.30 The HDS catalytic potential of zeolite incorprated into conventional NiMo or NiW/Al2O3 catalysts need to be further investigated. In this paper, a series of hydrodesulfurization catalysts of Ni-W supported on γ-Al2O3-MB (denoted as AMB) composites with various amounts of H-type β zeolite (denoted as MB) synthesized from kaolin were prepared. The hydrotreating performances of the MB-Al2O3 (AMB) composite-supported Ni-W catalysts using fluidized catalytic cracking (FCC) diesel as a feedstock were investigated. 2. Experimental Section 2.1. Preparation of MB and AMB Composite Supports. MB was prepared by in situ crystallization method from kaolin, which (24) Lecrenay, E.; Mochida, I. Stud. Surf. Sci. Catal. 1997, 106, 333– 342. (25) Michaud, P.; Lemberton, J. L.; Pe´rot, G. Appl. Catal., A 1998, 169, 343–353. (26) Yumoto, M.; Usui, K.; Watanabe, K.; Idei, K.; Yamazaki, H. Catal. Today 1997, 35, 45–50. (27) Kunisada, N.; Choi, K.; Korai, Y.; Mochida, I. Appl. Catal., A 2004, 260, 185–190. (28) Corma, A.; Fornes, V.; Monton, J. B.; Orchilles, A. V. J. Catal. 1987, 107, 288–295. (29) Ali, M. A.; Tasumi, T.; Masuda, T. Appl. Catal., A 2002, 233, 77– 90. (30) Ding, L.; Zheng, Y.; Zhang, Z.; Ring, Z.; Chen, J. J. Catal. 2006, 241, 435–445.

Energy & Fuels, Vol. 23, 2009 3847 has been described in elsewhere.31 H-MB was obtained by calcining the NH4+ form of MB at 500 °C for 5 h. H-MB powder was dispersed uniformly in deionized water, which was added dropwise into the pseudoboehmite (Shandong SenChi Co.) sol. Subsequently, the sol mixture was stirred vigorously in a water bath at 75 °C until the mixture became a viscous paste, which was dried and calcined at 550 °C for 4 h, ready for metal impregnation. Then the obtained composite support denoted as AMBi, herein i ) 1-4, the MB weight ratios in AMB1-AMB4 supports were 4.5, 16, 32, and 46 wt %, respectively. 2.2. Preparation of Supported NiW Catalysts. The supported NiW catalysts were prepared by a coimpregnation method with AMB and Al2O3 supports using the incipient-wetness method with an aqueous solution of the appropriate amounts of ammonium metatungstate hydrate [(NH4)6W12O39 · H2O] and nickel nitrate hexahydrate [Ni(NO3)2 · 6H2O]. After impregnation, the obtained precursors were dispersed in an ultrasonic bath for 30 min. The prepared samples were dried at 110 °C for 12 h and calcined at 500 °C for 4 h. All the catalysts were prepared with the constant amounts of W and Ni (27 wt % WO3, 3.5 wt % NiO). 2.3. Catalyst Characterization. N2 of samples were performed on a Micromeritics ASAP 2020 automated gas adsorption system. All the samples were degassed at 350 °C under vacuum prior to N2 adsorption at -196 °C. Microscopic morphology observations of samples were carried out using a Cambridge S-360 SEM. The nature of acid sites of the catalysts was determined by pyridineadsorbed Fourier transformed infrared (Py-FTIR) spectroscopy experiments on a MAGNAIR 560 FTIR instrument (Nicolet Co., America) with a resolution of 1 cm-1. The samples were dehydrated at 500 °C for 5 h under a vacuum of 1.33 × 10-3 Pa, followed by the adsorption of purified pyridine vapor at ambient temperature for 20 min. IR spectra of pyridine-adsorptions at various temperatures were recorded. The Bro¨nsted and Lewis acid sites could be determined by the bands of chemisorbed pyridine at 1540 cm-1 and coordinative bonded pyridine at 1450 cm-1, respectively. X-ray powder diffraction (XRD) profiles were recorded in an XRD-6000 diffractometer using Cu KR radiation under 40 kV and 30 mA in the scan range from 5° to 80° at a rate of 4° min-1. H2-TPR was carried out using 10% hydrogen in argon at a constant flow rate of 40 mL · min-1, from room temperature to 1000 °C, at a heating rate of 10 °C · min-1. The HRTEM measurements of the sulfided catalysts were carried out on a Philips Tecnai G2 F20 transmission electron microscope operated at an accelerating voltage of 200 kV. The catalysts were sulfided with a 2 wt % CS2/cyclohexane mixture at 320 °C for 6 h and kept in cyclohexane before measurement. The XPS spectra of the samples were taken on an ESCA Lab 220iXL electron spectrometer (VG) using 300 W Mg KR radiation. The binding energies were referenced to C1s line at 284.6 eV as reference. 2.4. Catalytic Activity Measurement. Catalytic performances were measured using a continuously flowing tubular high-pressure fixed-bed microreactor. The catalysts (2 g, grain size of 0.3-0.5 mm) were diluted with quartz particles before being loaded into the reactor. All catalysts were presulfided for 6 h with a 2 wt % CS2-cyclohexane mixture at a liquid hourly space velocity (LHSV) of 1.0 h-1, 320 °C, 4.0 MPa of total pressure, and H2/cyclohexane ratio of 600 mL · mL-1. Hydrodesulfurization tests of diesel were mainly carried out under the conditions of 350 °C, 5.0 MPa, 600 mL · mL-1, and 1.0 h-1, except for the cases to optimize the process conditions. Catalytic activities were determined at steady state after 13 h on-stream. The total sulfur content of diesel feed is 1300 ppm. The influence of reaction conditions on the HDS of diesel oil feed also was investigated. Table 1 summarizes the reaction conditions used in the present studies. The total sulfur content of the feed and products was measured by using a LC-4 coulometric sulfur analyzer system. The distributions of sulfur species in feed and products were determined by (31) Wan G., Duan A., Zhang Y., Zhao Z., Jiang G., Zhang D., Gao Z. Zeolite beta synthesized with acid-treated metakaolin and its application in diesel hydrodesulfurization. Submitted to Catal. Today (Ms. Ref. No.: CATTOD-D-08-00289).

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Wan et al. Table 2. Textural Properties of the Supports and the Catalysts

Table 1. Reaction Conditions process operation parameters

temperature effect

LHSV effect

H2/oil effect

pressure effect

temperature (°C) pressure (MPa) H2/oil ratio (mL · mL-1) LHSV (h-1)

340-370 5 600 1

350 5 600 0.5-2

350 5 400-1000 1

350 4-7 600 1

Finnigan Trace GC/MS with a Trace Ultral gas chromatograph using a HP-5MS (30 × 0.25 × 0.25) capillary column and a pulsed flame photometric detector (PFPD).

3. Results and Discussion 3.1. Characterization of Composite Supports and NiW Catalysts. 3.1.1. XRD. The XRD patterns of the AMB supports are shown in Figure 1A. From Figure 1A, the characteristic diffraction peaks of γ-Al2O3 (2θ ) 46.3° and 66.7°) and β-zeolite (2θ ) 22.4° and 7°) are observed for the AMB supports. With the increasing of MB content, the diffraction peak intensities of MB increase, while those of of γ-Al2O3 decrease. The XRD patterns of NiW/AMB oxide catalysts are shown in Figure 1B. No XRD diffraction peaks assigned to crystallines of NiO or NiAl2O4 are found in the oxide catalysts, indicating that nickel oxide species are present as crystallites smaller than 4 nm, which is below the detection limit of XRD, or nickel oxides are amorphous. In fact, for NiW/AMB4 catalyst with the highest MB content, the characteristic peaks corresponding to WO3 are observed by XRD. The characteristic diffraction peaks of γ-Al2O3 appeared in all oxide catalysts. The characteristic diffraction peaks of zeolite β (2θ ) 22.4° and 7°) can be detected for MB-containing catalysts. Compared with the AMB supports in Figure 1A, the characteristic diffraction peak intensities of MB in supported NiW catalysts are weakened to some extent, due to the dilution effect or partial breakdown of zeolite structure caused by the metal oxides.32,33

Figure 1. The XRD patterns of the AMB supports (A) and the oxidic NiW/AMB catalysts.

samples Al2O3 AMB1 AMB2 AMB3 AMB4 NiW/Al2O3 NiW/AMB1 NiW/AMB2 NiW/AMB3 NiW/AMB4

SBET/m2 · g-1 pore volume/cm3 · g-1 average diameter/nm 203.0 209.4 237.0 270.9 315.9 126.8 130.0 145.5 194.1 230.6

0.31 0.30 0.29 0.29 0.31 0.21 0.20 0.20 0.22 0.19

5.4 5.2 4.4 3.9 3.6 5.3 5.0 4.2 3.7 3.4

3.1.2. N2 Adsorption. Textural properties of the composite supports and the catalysts are listed in Table 2. The surface areas of NiW catalysts increase and the average diameters decrease when MB is introduced to the catalyst supports. However, for either support or catalyst, the addition of MB slightly decreases the pore volumes. Figure 2 shows the nitrogen adsorption/desorption isotherms of AMB-supported NiW oxide catalysts. From Figure 2, it can be seen that the nitrogen adsorption/desorption isotherms of all catalysts are of the type IV pattern. The pore size distributions of the supports and catalysts in Figure 3A,B show the preservation of the mesoporous structure in the supports and catalysts. Meanwhile, pore sizes of supports were centered around 4-5 nm and those of catalysts are around 3.5-4 nm, which are slightly smaller than those of the corresponding supports. 3.1.3. TPR. The H2-TPR profiles of the AMB-supported NiW oxide catalysts are given in Figure 4. The TPR profiles of all NiW catalysts show two principal reduction peaks in the temperature ranges of 600-800 and 800-1000 °C, respectively. The broad peak at high temperature can be assigned to the superimposed reduction of tetrahedrally coordinated W species and Ni species, and the low-temperature peak can be assigned to the reduction of polymeric octahedral W species.34-38 Moreover, with the increase of MB content, the locations of two intense peaks of NiW/AMB catalysts shift toward lower temperatures, demonstrating that metal oxide species have weaker interaction with the AMB support than that with Al2O3 support. So, the addition of MB is beneficial to tuning the metal-support interactions, which causes easier reduction of nickel and tungsten. Similar findings were also reported by Solis et al.39 3.1.4. TEM. Figure 5 showed the representative HRTEM images of the sulfided NiW/Al2O3 and NiW/AMB3. The dark fringes in the images are WS2 crystallites. The particles of the promoter Ni sulfide on the catalysts are too small to be seen in the images.40,41 It can be seen that NiW/Al2O3 catalyst shows

Figure 2. The nitrogen adsorption/desorption isotherms of supported NiW oxide catalysts.

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Figure 5. The HRTEM images of (a and a0) the sulfided NiW/Al2O3 and (b and b0) NiW/AMB3 catalysts.

Figure 3. The pore size distributions of the supports (A) and the supported NiW oxide catalysts (B).

Figure 4. The H2-TPR profiles of the supported NiW oxide catalysts.

mostly single-layer slabs, whereas NiW/AMB3 shows mostly multilayered WS2 slabs. On the basis of statistical analysis results in 15 images including 240-280 slabs which were taken from the different (32) Bendezu´, S.; Cid, R.; Fierro, J.L. G.; Lo´pez Agudo, A. Appl. Catal., A 2000, 197, 47–60. (33) Cid, R.; Neira, J.; Godoy, J.; Palacios, J. M.; Mendioroz, S.; Lo´pez Agudo, A. J. Catal. 1993, 141, 206–218. (34) Vermaire, D. C.; Vanberge, P. C. J. Catal. 1989, 116, 309–317. (35) Karakonstantis, L.; Matralis, H.; Kordulis, C.; Lycourghiotis, A. J. Catal. 1996, 162, 306–319. (36) Barton, D. G.; Soled, S. L.; Meitzner, G. D.; Fuentes, G. A.; Iglesia, E. J. Catal. 1999, 181, 57–72. (37) Horsley, J. A.; Wachs, I. E.; Brown, J. M.; Hardcastle, G. H.; Via, F. D. J. Phys. Chem. 1987, 91, 4014–4020. (38) Scheffer, B.; Molhoek, P.; Moulijn, J. A. Appl. Catal. 1989, 46, 11–30. (39) Solı´s, D.; Lo´pez Agudo, A.; Ramı´rez, J.; Klimova, T. Catal. Today. 2006, 116, 469–477. (40) Glasson, C.; Geantet, C.; Lacroix, M.; Labruyere, F.; Dufresne, P. J. Catal. 2002, 212, 76–85. (41) Reinhoudt, H. R.; Langeveld van, A. D.; Kooyman, P. J.; Stockmann, R. M.; Prins, R.; Zandbergen, H. W.; Moulijn, J. A. J. Catal. 1998, 179, 443–450.

Figure 6. Slab length distribution (A) and stacking layer number distribution (B) of the WS2 slabs on the sulfided NiW/γ-Al2O3 and NiW/AMB3 catalysts.

parts of each catalyst, the lengths and stacking numbers distributions of the WS2 slabs on NiW/Al2O3 and NiW/AMB3 are presented in Figure 6A,B. For NiW/Al2O3 catalyst, the average slab length is 4.1 nm, and the average layer number is 1.8. For NiW/AMB3 catalyst, the average length of WS2 slabs is 9.4 nm, and the average layer number is 3.1. Compared with NiW/Al2O3, NiW/AMB3 exhibits a broader distribution in slab length and layer number. This could be likely attributed to the different textures of the support, due to the coexistence of Al2O3 and MB. Higher WS2 stacking in sulfided NiW/AMB3 might

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Figure 8. The deconvolution XPS spectra of W4f for NiW sulfided catalysts (a) NiW/Al2O3 and (b) NiW/AMB3.

Figure 7. XPS spectra of W4f (A) and XPS spectra of Ni2p (B) for NiW oxide catalysts: (a) NiW/Al2O3 and (b)NiW/AMB3.

be formed due to a lower metal-support interaction, which leads to a type II WS2 phase. The multilayered WS2 slabs can provide a higher density of multivacancies and enhanced the HYD activity42,43 compared with single layered or thin slabs. Longer WS2 slab length of sulfided NiW/AMB3 resulted from lower dispersion of metal oxide precursor, which was confirmed by XRD results. The morphlogy of WS2 structures on NiW/AMB3 was more curved and such curved sites in the WS2 crystallites probably formed more vancant sites of sulfur; hence, more catalytically active sites might be formed. 3.1.5. XPS. Figure 7A,B shows XPS spectra of NiW/Al2O3 and NiW/AMB3 oxide catalysts. The spectra of the oxide catalysts have a doublet peak of W4f5/2 and W4f7/2 electrons at binding energy (BE) positions of 37.8-37.9 and 35.7-35.8 eV, respectively. These peaks are assigned to W(VI) species, most likely to be WO3.44,45 NiW/Al2O3 have higher BEs of W4f and Ni2p core levels compared with those of MB-containing NiW/ AMB3 catalyst, suggesting that the addition of MB weakens the interaction of W with the support and/or Ni,30 which is consistent with the TPR results. The deconvolution W4f spectra of sulfided NiW/Al2O3 and NiW/AMB3 catalysts are shown in Figure 8.32 On the basis of the relationship equation of Wsulfide/Wtotal ) Wsulfide/(Woxide + Wsulfide), the degree of sulfidation of W species is determinded from the fit curves (Figure 8). The results show that the sulfidation degree of W species in NiW/AMB3 (50%) is much higher than that of NiW/Al2O3 (42%), which is likely due to various degrees of interaction of W species with the support in (42) Hensen, E. J. M.; Kooyman, P. J.; van der Meer, Y.; van der Kraan, A. M.; de Beer, V. H. J.; van Veen, J. A. R.; van Santen, R. A. J. Catal. 2001, 199, 224–235. (43) Hensen, E. J. M.; de Beer, V. H. J.; van Veen, J. A R.; van Santen, R. A. Catal. Lett. 2002, 84, 59–67. (44) Ng, K. T.; Hercules, D. M. J. Phys. Chem. 1976, 80, 2094–2102. (45) Salvati Jr., L.; Makovsky, L. E.; Stencel, J. M.; Brown, F. R.; Hercules, D. M. J. Phys. Chem. 1981, 85, 3700–3707.

Figure 9. FT-IR spectra of pyridine adsorption on supported NiW oxide catalysts degassed at 200 °C (A) and at 350 °C (B).

NiW/Al2O3 and NiW/AMB3 catalysts. High sulfidation degree may lead to more type-II WS2 phase, which is favorable for getting higher HDS activity.42,43 3.1.6. FT-IR of Pyridine Adsorption. The FT-IR spectra of pyridine adsorption degassed at 200 and 350 °C on the NiW oxide catalysts in the region of 1700-1400 cm-1 are shown in parts A and B of Figure 9, respectively. According to the literature,46,47 the characteristic bands at 1540 and 1450 cm-1 are assigned to pyridine adsorbed on the Bro¨nsted (B) acid sites and Lewis (L) acid sites, respectively. The amount of pyridine adsorption degassed at 200 °C corresponds to the total acid amount, whereas that at 350 °C corresponds to the acid amount of strong and medium strength acid. Table 3 shows that total acid amounts (B + L) of AMB3 are higher than that of Al2O3 support, due to the introduction of MB. The Al2O3 support possesses only L acid sites and AMB3 support possesses both (46) Poncelet, G.; Dubru, M. L. J. Catal. 1978, 52, 321–331. (47) Lee, J. S.; Boudart, M. Catal. Lett. 1993, 20, 97–106.

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Table 3. Amounts of B and L Acid Sites Determined by FT-IR of Pyridine Adsorption for Supports and NiW Catalysts at Different Degassed Temperatures amount of acid sites at 200 °C (µmol · g-1)

amount of acid sites at 350 °C (µmol · g-1)

sample

L

B

B+L

B/L

L

B

B+L

B/L

Al2O3 AMB3 MB NiW/Al2O3 NiW/AMB1 NiW/AMB2 NiW/AMB3 NiW/AMB4

486.90 466.67 252.38 620.24 358.33 297.62 397.62 294.05

0.00 37.29 252.54 45.76 40.68 44.07 59.32 55.93

486.90 503.96 504.92 666.00 399.01 341.69 456.94 349.98

0.00 0.08 1.00 0.07 0.11 0.15 0.15 0.19

386.90 353.57 247.62 292.86 141.67 108.33 170.24 130.95

0.00 27.46 228.81 37.46 22.03 28.81 27.12 33.90

386.90 381.03 476.43 330.32 163.70 137.14 197.36 164.85

0 0.08 0.92 0.12 0.16 0.27 0.16 0.26

L and B acid sites. After loading of WO3, all NiW catalysts show the presence of both L and B acid sites. The addition of the MB results in the change of the ratio of B/L in both total acid and strong acid. Hence, the addition of MB to the NiW catalyst not only affects the total amount of acidic sites, but also increases the ratio of B/L. 3.1.7. HDS ActiVity EValuation. Hydrodesulfurization tests of diesel were carried out under the reaction conditions of 350 °C, 5.0 MPa, 600 mL · mL-1, and 1.0 h-1 over all the catalysts including the commercial HDS catalyst RN-10 (supplied by Fushun refinery). The HDS efficiency results are shown in Figure 10. Among all the catalysts, NiW/AMB3 catalyst shows the highest HDS efficiency, so the optimal MB content is 32 wt % in composite AMB support. The sulfur contents in the products after the HDS reaction over NiW/AMB3 and NiW/ Al2O3 are 16.7 and 32.2 ppm, respectively. From Figure 11 and Table 4, NiW/AMB3 exhibits a higher HDS conversion of alkylsubstituted DBT than NiW/Al2O3. The sulfur compounds in the feedstock are primarily alkylbenzothiophenes (alkyl-BT) and alkyldibenzothiophenes (alkyl-DBT).

Figure 10. The HDS efficiencies of supported NiW catalysts.

Figure 11. The sulfur compounds in feed and in product after HDS.

Table 4. Sulfur Compounds in Feed and in Products after HDS over NiW/Al2O3 and NiW/AMB3 sulfur compound

feed (ppm)

NiW/Al2O3 (ppm)

NiW/AMB3 (ppm)

BT C1-BT C2-BT gC3-BT DBT C1-DBT C2-DBT gC3-DBT total

28.8 145.2 249.5 345.2 53.8 135.1 146.2 196.3 1300

11.8 20.4 32.2

8.0 8.7 16.7

The addition of the appropriate amount of MB to the catalyst support resulted in a higher HDS catalytic activity than that of the conventional alumina-supported catalyst, and the increase in HDS activity was associated with the enhanced hydrogenation activity and the appropriate B/L ratio. The enhancement in hydrogenation activity was likely associated with the domain sizes of hydrogenation active sites, WS2. Multilayered WS2 slabs provided a higher density of multivacancies compared with single-layered slabs. The single-slab structure (type I) interacted strongly with the support, whereas the multiple-slab conformation (type II) had weak interaction with the support and exhibited greater HYD activity.42,43,48-50 The sulfidation of W and WS2 slab sizes on the catalysts increased significantly, and this could lead to an increase of catalytic hydrogenation activities. The acidity was also important for enhancing HDS activities of zeolite-containing catalysts. The addition of MB led to a change of the proportion of B acid or the ratio of B/L. The suitable ratio of B/L would be favorable for high HDS conversion. Therefore, the ratio of B/L and acid strength seemingly played an important role in promoting HDS performance of the catalysts. 3.1.8. Influence of Processing Conditions. The influence of operating conditions on the catalytic performance of NiW/ AMB3 catalyst for the HDS of diesel feed was investigated. The data presented in Figure 12A show that the total sulfur in the product steadily decreases with the increasing of reaction temperature in the range of 340-370 °C. The ultradeep desulfurization of FCC diesel oil in which the sulfur content is below 10 ppm in the product can be achieved over NiW/AMB3 catalyst at reaction temperature of 360-370 °C under the other reaction conditions of LHSV ) 1 h-1, H2/oil ratio ) 600, P ) 5 MPa. Figure 12B illustrates the influence of LHSV on the degree of desulfurization. It is observed that desufurization is significantly influenced by the LHSV. When the LHSV is less than 1, the ultradeep desulfurization of FCC diesel oil whose sulfur content is below 10 ppm in the product can be obtained under (48) Topsøe, H.; Clausen, B. S.; Topsøe, N.-Y.; Zeathen, P. Stud. Surf. Sci. Catal. 1989, 53, 77–102. (49) Topsøe, H.; Clausen, B. S. Appl. Catal. 1986, 25, 273–293. (50) Vradman, L.; Landau, M. V.; Herskowitz, M. Fuel 2003, 82, 633– 639.

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Figure 12. Effect of the process parameters on the total sulfur removal from FCC diesel oil feed: A, operating temperature; B, LHSV; C, pressure; D, H2/oil ratio.

the other conditions of reaction temperature of 350 °C, the pressure of 5 MPa, and H2/oil ratio of 600. The results presented in Figure 12C indicated that an increase in hydrogen pressure leads to a marginal improvement in sulfur removement. Thus, for example, from 4 to 7 MPa, the sulfur content in the product was lowered from 18.3 to 12.1 ppm. The H2/oil ratio has a nonsignificant influence on FCC diesel oil desulfurization (Figure 12D). The results of the present studies reveal that the desulfurization of diesel oil is remarkably influenced by reaction temperature and space velocity. Ultralow sulfur (360 °C) or low LHSV (e.g.,