796r 2009 American Chemical Society pubs.acs.org/EF

Energy Fuels 2010, 24, 796–803 : DOI:10.1021/ef901098mPublished on Web 12/14/2009

Preparation and Evaluation of the Composite Containing USL Zeolite-Supported NiW

Catalysts for Hydrotreating of FCC Diesel

Aijun Duan,† Zhenyong Gao,† Quan Huo,‡ Chengyin Wang,† Dengqian Zhang,†

Mingcheng Jin,† Guiyuan Jiang,† Zhen Zhao,*,† Huifang Pan,‡ and Keng Chung§

†State Key Laboratory ofHeavyOil Processing, ChinaUniversity of Petroleum, Beijing 102249, P.R. China, ‡TheKey Laboratoryof Catalysis, China National Petroleum Corp. (CNPC), China University of Petroleum, Beijing 102249, P.R. China, and

§Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, T2N 1N4, Canada

Received September 29, 2009. Revised Manuscript Received November 19, 2009

Two different ways, including an in situ synthetic method and a mechanical mixing method, were used tocombine zeolite USL (ultra stable L) with alumina for preparation of a new composite support material ofhydrotreating catalyst. The physicochemical properties of samples were characterized by means of XRD,N2 physisorption, SEM, FT-IR, 27Al MAS NMR, NH3-TPD, H2-TPR, and UV-vis DRS. Compositesupports containing different contents of zeolite USL andAl2O3were prepared by in situ synthetic methodbased on amodified pH-swingmethod,which showed a higher specific surface area, pore volume, aswell asaverage pore diameter compared with the supports prepared via a mechanical mixing method. Corres-ponding NiW/γ-Al2O3-USL series catalysts were obtained by the incipient-wetness impregnationmethod, and the activities of these catalysts for FCC diesel hydrodesulfurization (HDS) and hydrodeni-trogenation (HDN) were evaluated in a high-pressure microreactor system. The assessment resultsindicated that the catalyst with 10 m% USL in the support prepared by the in situ method showed thehighest HDS andHDN conversions, which reached a maximum of 99.3% and 94.1% for HDS andHDN,respectively. In addition, the swing pH method plays an important role in preparation of the Al2O3

support, and NiW/γ-Al2O3(P) (prepared by the swing pH method) catalyst also gave better performancefor the HDS and HDN of diesel oil. These activities were much higher than those over a kind of industrialcatalyst of RN10 and were also better than the corresponding catalyst in which the support was obtainedby the mechanical mixing method.

1. Introduction

With the increasing awareness of environmental protection,more stringent legislation was introduced throughout theworld to limit the sulfur content of transportation fuels.1-3

On the contrary, crude oil and feedstocks for refinery pro-cesses to produce vehicle fuels became more and more heavyand deteriorative, leading to higher sulfur contents in FCCdiesels and gasoline. The properties of those fuel productswere far beyond the standards of clean fuel specifications. Thetraditional hydrotreating process is one of themost importanttechniques to remove the sulfur and nitrogen heteroatomiccompounds for producing clean transportation fuels.4 How-ever, it would be a great challenge to obtain the ultra-lowsulfur fuels only depending on the common traditional hydro-treating techniques.5,6 Thus, how to improve the efficiency ofhydrotreating catalysts is one of the most urgent choices forthe ultra deep hydrodesulfurization (HDS) process. The

activity and selectivity of HDS catalysts are obviously suscep-tible to their supports. The catalyst support plays a key role inthe dispersion of the active components and promoters, andalso affects the morphology and catalytic performancethrough metal-support interaction. So, increasing attentionworldwide is being paid to the development and design of newsupports for hydrotreating catalysts.7,8

Zeolites are well-known for their high specific surface areasand high activities in many catalytic reactions. However, highacidity of zeolites will result in deep cracking or secondaryreactions in the catalytic processes. For the deep desulfuriza-tion reactions, for example, it should be required a suitabledegree of acidic functionality in order to improve the ring-opening of heterocyclic aromatic components, which is priorto the conversions of organic heteroatomic compounds toinorganic sulfur and nitrogen species.9 It has been reportedthat the incorporation of acidic zeolites in catalysts couldpromote the hydroisomerization anddealkylation activities ofa catalyst.10,11 On the other hand, these acidic materialstended to possess either only micropores (less than 2 nm) or*Towhom correspondence should be addressed. Telephone: (þ8610)

89731586. Fax: (þ8610) 69724721. E-mail: zhenzhao@cup.edu.cn.(1) Duan, A. J.; Li, R. L.; Jiang, G. Y.; Gao, J. S.; Zhao, Z.; Wan,

G. F.; Zhang, D. Q.; Huang, W. Q.; Chung, K. H. Catal. Today 2009,140, 187–191.(2) Huang, W. Q.; Duan, A. J.; Zhao, Z.; Wan, G. F.; Jiang, G. Y.;

Dou, T.; Chung, K. H.; Liu, J. Catal. Today 2008, 131, 314–321.(3) Li, X.; Wang, A. J.; Egorova, M.; Prins, R. J. Catal. 2007, 250,

283–293.(4) Landau, M. V.; Herskowitz, M.; Hoffman, T.; Fuks, D.; Liverts,

E.; Froumin, D.V. N. Ind. Eng. Chem. Res. 2009, 48, 5239–5249.(5) Saih, Y.; Segawa, K. Appl. Catal., A 2009, 353, 258–265.(6) Song, C. S. Catal. Today 2003, 86, 211–263.

(7) Breysse, M.; Afanasiev, P.; Geantet, C.; Vrinat, M. Catal. Today2003, 86, 5–16.

(8) Murali Dhar, G.; Srinivas, B.N.; Rana,M. S.; Kumar,M.;Maity,S. K. Catal. Today 2003, 86, 45–60.

(9) Arias, P. L.; Cambra, J. F.; G€uemez, B.; Legarreta, J. A.; Pawelec,B.; Fierro, J. L. G. Bull. Soc. Chim. Belg. 1995, 104, 197–204.

(10) Isoda, T.; Nagao, S.; Ma, X. L.; Korai, Y.; Mochida, I. EnergyFuels 1996, 10, 1078–1082.

(11) Bataille, F.; Lemberton, J. L.; P�erot, G.; Leyrit, P.; Cseri, T.;Marchal, N.; Kasztelan, S. Appl. Catal., A 2001, 220, 191–205.

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Energy Fuels 2010, 24, 796–803 : DOI:10.1021/ef901098m Duan et al.

only mesopores (2-50 nm), in most cases only micropores.11

The small microporous configurations limited the diffusion ofexternal molecules to access the catalytic active sites inside themicropores, and also weakened the following diffusion pro-cesses of product molecules from the catalytic active sites tothe outside of the pores. Therefore, the reasonable combina-tion of zeolite with other materials would not only adjust theacidic functionality and metal-support interaction but alsoimprove the pore structures of catalysts.Generally, afterHDSprocess, the sulfur molecules remaining in the fuel productsare mainly refractory dialkyldibenzothiophenes, such as 4,6-dimethyldibenzothiophene (4,6-DMDBT),which are difficultto be removed from the fuels via hydrogenolysis route.12-15

The highly active catalysts with suitable acidity and adaptablesurface physicochemical properties should be facilitated toameliorate the mass-transfer steps, and will also be propitiousto increase the efficiency of the catalyst utilization.

As a kind of special zeolite, zeolite L possesses a LTL typeframework topology and hexagonal crystalline structurewith one-dimensional configuration, which is bounded by12-membered-ring pores with an aperture of about 0.71 nm,leads to the formation of cavities of about 0.48 � 1.24 �1.07 nm. The Si/Al ratio of framework is typically 3.0. Hence,a typical chemical composition of zeolite L is K9(AlO2)9-(SiO2)27 per unit cell (puc).16-19 This type of zeolite L wasmostly used in the processes such as Fischer-Tropsch (F-T)Synthesis,20 dehydrogenation and cyclization,21,22 catalyticreforming,23 and other processes.24 However, there arefew published research reports on using zeolite L in HDSprocess,25,26 especially no open report to use zeolite L as acidiccomponents of catalyst for upgrading the low grade dieseldistillates in the hydrotreating process. The design and com-posite method of zeolite L combine with conventional NiMoor NiW/Al2O3 catalysts should be further investigated toanalyze the potential utilization in the catalytic HDS process.

In this work, with the aim to increase the hydrogenationactivity of NiW catalysts, some novel type of hydrotreatingcatalyst supports containing zeolite USL were prepared byusing the mechanical mixing method and in situ syntheticmethod based on a modified pH-swing method. The catalyticactivity measurements were carried out to investigate the

effects of zeolite contents in composite supports on HDSandHDNperformances of NiW/Al2O3-USL series catalystswith diesel feedstock.

2. Experimental Section

2.1. Preparation of Al2O3-USL Composite Supports. ZeoliteUSL (SiO2/Al2O3 molar ratio = 12.9) in the protonic form wassupplied by the Key Laboratory of Catalysis, China NationalPetroleum Corp. of China University of Petroluem.27

Two types of composite supports were used in this work. Onewas a physical mixture of alumina and zeolite L that wasdenoted asAl2O3-USL(M) and obtained bymechanical mixingmethod, and the other was a micromesoporous compositeprepared by in situ overgrowing mesoporous alumina overUSL zeolite crystals. The obtained composite support wasdenoted as Al2O3-USL (C).

2.1.1. In Situ Synthetic Method. Alumina support andAl2O3-USL(C) composite supports were all synthesized by amodified pH-swing method28 in this study. All preparationoperations were carried out at a constant temperature of70 �C. The initial pH-swing cycle was as follows: (1) 60 mL ofaqueous Al2(SO4)3 3 18H2O (acid pH) was contained in a glassvessel, denoted as solution A; (2) an aqueous NaAlO2 solution(basic pH), denoted as solution B; was dropped into solution Auntil the mixture reached pH 9, and aged for 5 min; (3) thenanother 60 mL of aqueous Al2(SO4)3 3 18H2O solution wasadded dropwise until the whole solution reached to about pH3. (4) A white precipitate appeared and kept for 5 min, and wascontinually dropping with NaAlO2 solution until the pH was 9.This stage was the first pH-swing cycle. In this work, the aboveprocess was repeated for 4 times to obtain the supportmaterials.After completing pH-swing cycles for four times, the finalsolution was aged for 60 min at pH of 9. The resulting slurrywas filtered and washed by deionized water at 60 �C, then theobtained cake was dried at 120 �C and calcined at 550 �C for 4 h.In the mentioned procedure above, zeolite USLwere added intothe composite at pH of 3 in the first cycle. Hereby the obtainedsupports were labeled asAl2O3-USL-x(C), where x representedthe contents of USL in the total supports, and is equal to 0, 10,20, 30, and 40 m% respectively.

2.1.2.MechanicalMixingMethod.For comparison purposes,Al2O3-USL(M)were also obtained. Themechanical mixture ofUSL, pseudoboehmite powder, some amounts of nitric acid,and deionized water were first extruded, then dried at 120 �C for4 h, and finally calcined at 550 �C for 4 h.

2.2. Preparation of Supported NiW Catalysts. The Al2O3-USL or Al2O3-supported NiW catalysts were prepared bycoimpregnation and the incipient-wetness method with an aqu-eous solution of the appropriate amounts of ammonium meta-tungstate hydrate [(NH4)6W12O39 3H2O] and nickel nitratehexahydrate [Ni(NO3)2 3 6H2O]. After the impregnation step,the obtained precursors were dispersed in an ultra sonic bath for20 min. The prepared catalyst samples were dried at 120 �C for12 h and calcined at 550 �C for 4 h. All the catalysts were loadedwith the constant amounts of W and Ni contents (27 m%WO3,3.5m%NiO). A kind of commercial catalyst RN-10 was used asthe reference catalyst.

2.3. Catalyst Characterizations. The composite supports andthe catalysts were characterized by means of XRD, SEM, N2

physisorption, FT-IR, 27Al MAS NMR, NH3-TPD, H2-TPR,and UV-vis DRS, etc. X-ray powder diffraction (XRD) pro-files were recorded in anXRD-6000 diffractometer usingCuKRradiation under 40 kV, 30mA, scan range from 5 to 75� at a rateof 4� 3min-1. BET surface area, average pore volume, and porediameter were determined by using the ASAP 2020 automated

(12) Meng,X.C.;Wu,Y.X.; Li, Y.D. J. PorousMater. 2006, 13, 365–371.(13) Zhang, H. J.; Meng, X. C.; Li, Y. D.; Lin, Y. S. Ind. Eng. Chem.

Res. 2007, 46, 4186–4192.(14) Song, C.; Ma, X. Appl. Catal., B 2003, 41, 207–238.(15) Bataille, F.; Lemberton, J. L.;Michaud, P.; P�erot,G.; Vrinat,M.;

Lemaire, M.; Schulz, E.; Breysse, M.; Kasztelan, S. J. Catal. 2000, 191,409–422.(16) Pichat, P.; Franco Parra, C.; Barthomeuf, D. J. Chem. Soc.,

Faraday Trans. I 1975, 71, 99.(17) Bhat, S. D.; Niphadkar, P. S.; Gaydhankar, T. R.; Awate, S. V.;

Belhekar, A. A.; Joshi, P. N.Microporous Mesoporous Mater. 2004, 76,81–89.(18) Koa, Y. S.; Ahn, W. S. Powder Technol. 2004, 145, 10–19.(19) Ohgushi, T.;Matsuo, T.; Satoh, H.;Matsumoto, T.Microporous

Mesoporous Mater. 2009, 117, 472–477.(20) Bengoa, J. F.; Alvarez, A. M.; Cagnoli, M. V.; Gallegos, N. G.;

Yeramian, A. A.; Marchetti, S. G. Mater. Lett. 2002, 53, 6–11.(21) Bernard, J. R. Proc. Int. Conf. Zeolites, 5th. Naples, Italy, June

2-6, 1980; Rees, L. V. C., Ed.; Heyden: London, Philadelphia, pp 686-695.(22) Fang,X.G.;Li,F.Y.;Luo,L.T.Appl.Catal.,A1996,146, 297–304.(23) Triantafillou, N. D.; Deutsch, S. E.; Alexeev, O.; Miller, J. T.;

Gates, B. C. J. Catal. 1996, 159, 14–22.(24) Ban, T.; Morimoto, J.; Ohya, Y. Mater. Chem. Phys. 2008, 109,

347–351.(25) Taniguchi, M.; Imamura, D.; Ishige, H.; Ishii, Y.; Murata, T.;

Hidai, M.; Tatsumi, T. J. Catal. 1999, 187, 139–150.(26) Tatsumi, T.; Taniguchi, M.; Ishige, H.; Ishii, Y.; Murata, T.;

Hidai, M. Appl. Surf. Sci. 1997, 121-122, 500–504.

(27) Huo, Q.; Li, Q.; Xu, Q. H.; Dou, T.; Pan, H. F. J. Fuel Chem.Technol. 2007, 35, 302–307.

(28) Ono, T.; Ohguchi, Y.; Togari, O. Preparation of Catalysts III,Elsevier Science Publisher: The Netherlands, 1983; pp 631-641.

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Energy Fuels 2010, 24, 796–803 : DOI:10.1021/ef901098m Duan et al.

gas adsorption system under vacuum prior to N2 adsorption at-196 �C. Scanning electron microscopy (SEM) observations ofsamples were performed using a Cambridge S-360 apparatus.FT-IR spectra were obtained in the wavenumber range from1200 to 400 cm-1 via an FTS-3000 spectrophotometer manu-factured by American Digilab company. For the transmissionIR experiments under ambient conditions, the measured waferwas prepared as KBr pellet with the weight ratio of sample toKBr for 1/100. The resolution was set at 4 cm-1 duringmeasurement. 27Al NMR spectra were acquired on a BrukerAVANCE 500 spectrometer operated at a resonance frequencyof 130 MHz, and 10 000 scans. Acidic amounts of the zeolitewere measured by temperature-programmed desorption (TPD)of ammonia (NH3-TPD) method. A 0.2 g sample with 40-80mesh was pretreated in helium at 500 �C for 2 h, cooled to120 �C, and adsorbed NH3 for 45 min. After flushing by purehelium gas at 120 �C for 1 h, TPD started at a rate of 5 �C 3min-1

from 120 to 600 �C, and the signal wasmonitoredwith a thermalconductivity detector (TCD).H2-TPRwas carried out using 10%hydrogen in heliumat a constant flow rate of 40mL 3min-1, from100 to 1000 �C, at a heating rate of 10 �C 3min-1. The hydrogenconsumption signal was monitored by a TCD. All the sampleswere degassed at 300 �C and before the outlet gases entering theTCD, a cooling trap and a filter packed with molecular sieve 5A(60-80meshes) were used to removeH2O andCO2. TheUV-visdiffuse reflectance spectra (DRS) experimentswere performed ona Hitachi U-4100 UV-vis spectrophotometer with the integra-tion sphere diffuse reflectance attachment, using BaSO4 asreference. The powder samples were loaded in a transparentquartz cell and were measured in the region of 200-800 nm atroom temperature.29,30

2.4. Catalytic Activity Measurement. Catalytic performanceswere evaluated in a high-pressure fixed-bed reactor with 2 g ofcatalyst (grain size of 0.3-0.5 mm). All catalysts were presul-fided for 4 h with 2 m% of CS2-cyclohexane mixture under theconditions of LHSV (liquid hourly space velocity) of 1.0 h-1,temperature of 320 �C, total pressure of 4 MPa, and aH2/cyclohexane ratio of 600 mL 3mL-1. The feedstock used inthis work was Daqing FCC diesel with 1290 ppm of S and907 ppm of N. The properties of the diesel oil feedstock areshown in Table 1. Hydrodesulfurization and hydrodenitrogena-tion tests were carried out under the conditions of 350 �C,5.0 MPa, 600 mL 3mL-1, and 1.0 h-1. Catalytic activities weremeasured at steady state after 13 h on-stream. The total sulfurcontent and nitrogen contents in the feed and products weremeasured by using a LC-4 coulometric sulfur analyzer system.The instrumental errors in N and S analysis were less than 3%.The catalytic activities under investigation were estimated byHDS and HDN conversions. The conversions are defined as

follows: HDS% conversion =[(Sf - Sp)/Sf] � 100%; HDN%conversion = [(Nf - Np)/Nf] � 100%, where Sf and Nf are thenitrogen and sulfur contents in feed (m%), and Sp andNp are thesulfur and nitrogen contents in products (m%), respectively.The rate constants for the removal of total sulfur or nitrogenwere calculated using eq 1 as shown below:31

k ¼ LHSV

n-1

1

Cn-1p

-1

Cn-1f

" #ð1Þ

where k is the apparent rate constant for conversion of sulfur ornitrogen presented in feedstock, h-1 (ppm)1-n, n is the order ofreaction, Cp is the total sulfur or nitrogen present in product(ppm),Cf is the total sulfur or nitrogen present in feed (ppm), andLHSV is the liquidhourly space velocity (h-1). The reactionordern depends on the boiling range of the petroleum fraction. Theprevious studies showed that the reaction orders of HDN andHDS of diesel could fit well with 1.5 and 2.0, respectively.32,33

Taken the activity ofRN-10 as a standard, which is denoted ask0,the relative activities of other catalysts are defined as follows:RAV= k/k0 � 100.

3. Results and Discussion

3.1. N2 Physisorption. The nitrogen adsorption-desorp-tion isotherms of Al2O3-USL composite supports startingfrom low to high pressures are shown in Figure 1. The N2

adsorption-desorption isotherms showed a typical hystere-sis loop in which isotherms were ascribed to type IV classi-fication (Figure 2), indicating the presence of framework-confined mesopores in spite of the different preparationmethods. As for the case of Al2O3-USL-40(M), the hyster-esis loop was not very broad (0.6 < P/P0 < 0.95), whereasthe hysteresis loop of Al2O3-USL-40(C) was relativelyextended, which was the characteristic of a solid with higherspecific area and mesopores.34 The BET surface areas ofsupports and catalysts are summarized in Table 2. Wideranges of differences were found for specific surface areas(310-200 m2

3 g-1), total pore volumes (1.02-0.32 mL 3 g

-1),and average diameters (13.8-9.15 nm), as the zeolite USLcontents were variable in the supports. It was easier to seethat Al2O3-USL-40(C) had a larger average pore diameter,and higher pore volume and specific surface area than

Table 1. Typical Properties of Diesel Feedstock

properties data

density @ 20 �C/g 3 cm-3 0.8798

S (μg 3 g-1) 1290

N (μg 3 g-1) 907

Distillation (�C) (ASTM D-86)IBP 15830% 21250% 23870% 279FBP 374

Hydrocarbon Compositions (% vol)aromatics 56.9olefin 8.4saturated hydrocarbon 34.7

Figure 1. N2 adsorption-desorption isotherms of Al2O3-USL-40(M) and Al2O3-USL-40(C).

(29) Wan, G. F.; Duan, A. J.; Zhao, Z.; Jiang, G. Y.; Zhang, D.; Li,R.; Dou, T.; Chung, K. H. Energy Fuels 2009, 23, 81–85.(30) Wan, G. F.; Duan, A. J.; Zhang, Y.; Zhao, Z.; Jiang, G.; Zhang,

D.; Gao, Z.; Liu, J.; Chung, K. H. Energy Fuels 2009, 23, 3846–3852.

(31) Ferdous, D.; Dalai, A. K.; Adjaye, J. Applied Catalysis A:General 2004, 260, 153–162.

(32) Bej, S. K.; Dalai, A. K.; Adjaye, J. Energy Fuels 2001, 15, 377–383.

(33) Yumoto, M.; Usui, K.; Watanabe, K.; Idei, K.; Yamazaki, H.Catal. Today 1997, 35, 45–50.

(34) Leyva, C.; Rana, M. S.; Ancheyta, J. Catal. Today 2008, 130,345–353.

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Energy Fuels 2010, 24, 796–803 : DOI:10.1021/ef901098m Duan et al.

Al2O3-USL-40(M). Similar results were obtained aftertungsten and nickel were supported. Therefore, it could befound that composite support based on the pH-swingmethod hadmuch better textural properties than those basedon themechanical mixingmethod, whichwould be favorablefor the hydrotreating performance of diesel.

3.2. XRD. Figure 2 shows the XRD patterns of compositesupports obtained from different preparation methods ofAl2O3-USL-40. Strong diffraction peaks located at 2θ of5.5, 19.4, 22.7, 28.0, 29.1, and 30.7� correspond to the LTLframework topology that existed in the XRD patterns ofAl2O3-USL-40(M) and Al2O3-USL-40(C),35 indicatingthat the structure of zeolite USL were well kept. The crystal-line structure of USL was retained even after the loadingsof nickel and tungsten (from Figure 3), but unfortunatelythe intensities of USL characteristic peaks were slightlyweakened in the XRD patterns of NiW/Al2O3-USL(C).The loss of crystallinity was probably ascribed to the dilutioneffect or distortion caused by the interaction of Ni or Wspecies with the zeolite framework.36,37 Additionally, noobvious peak of metal oxides was observed in the XRDpatterns of all catalysts, indicating that Ni and W speciesexisted as little crystallites smaller than the XRD limitationof 4 nm or were well dispersed on the surface of the supports.

3.3. SEM. The SEM images of Al2O3, zeolite USL,Al2O3-USL-40(M), and Al2O3-USL-40(C) are shown inFigure 4. From the Figure 4b, it could be illustrated that the

Al2O3 particles were presented as loose aggregates of amor-phousmorphology. The zeoliteUSLhad typical sheet crystals(around 700-1000 nm) with smooth surface(Figure 4a), andthe particles of zeolite USL and Al2O3 existed independentlyin Al2O3-USL-40(M) (Figure 4c). In Figure 4d, few Al2O3

aggregates of particles could be found in Al2O3-USL-40(C),but some particles, in which the morphologies were similar tozeolite USL (generally above 1000 nm), were observed. Thatmeant that the presence of zeoliteUSLparticles enwrappedbya film of Al2O3 in theAl2O3-USL-40(C) composite supports.

3.4. FT-IR. The FT-IR spectra of the Al2O3, zeolite USL,and Al2O3-USL composite supports are shown in Figure 5.For the USL sample, the peak at 990 cm-1 could be assignedto TO4 asymmetric stretching vibration. The peaks at 793and 678 cm-1 could be assigned to TO4 symmetric stretchingvibration, and peaks at 616 cm-1 to the bending vibration ofthe inner tetrahedral. The peak at 454 cm-1 was ascribed tothe double-annular vibration of the inner tetrahedral.38 Forthe support of Al2O3-USL-40(C), the peak attributed to thedouble-annular vibration of the inner tetrahedral shifted to

Table 2. Textural Properties of Supports and Catalysts

samplesSBET

(m23 g

-1)pore volume(cm3

3 g-1)

averagediameter (nm)

USL 110.9 0.092 3.12Al2O3(B)

a 234.5 0.946 16.14Al2O3(P)

b 310.8 1.02 13.80Al2O3-USL-40(M) 202.7 0.32 9.15Al2O3-USL-40(C) 242.2 0.71 11.80NiW/Al2O3 261.1 0.75 12.76NiW/Al2O3-USL-10(C) 237.8 0.74 11.61NiW/Al2O3-USL-40(C) 178.0 0.41 9.89NiW/Al2O3-USL-40(M)

140.2 0.28 8.11

aThe commercial Al2O3 bought from Shandong. bAl2O3 prepared bythe swing pH method.

Figure 2. The XRD patterns of the Al2O3-USL-40 supports pre-pared with different methods.

Figure 3. The XRD patterns of the NiW/Al2O3-USL(C) catalysts.

Figure 4. SEM images of (a) Al2O3; (b) zeolite USL; (c)Al2O3-USL-40(M); and (d) Al2O3-USL-40(C).

(35) Ko, Y. S.; Ahn, W. S. Bull. Korean Chem. Soc. 1999, 20, 1–6.(36) Bendez�u, S.; Cid, R.; Fierro, J. L. G.; L�opez Agudo, A. Appl.

Catal., A 2000, 197, 47–60.(37) Cid, R.; Neira, J.; Godoy, J.; Palacios, J. M.; Mendioroz, S.;

L�opez Agudo, A. J. Catal. 1993, 141, 206–218. (38) Ko, Y. S.; Ahn, W. S. Bull. Korean Chem. Soc. 1999, 20 (2), 1–6.

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Energy Fuels 2010, 24, 796–803 : DOI:10.1021/ef901098m Duan et al.

561 cm-1, which was lower than that of Al2O3-USL-40(M).In addition to this shift, a new peak at 1012 cm-1 appeared inthe FT-IR spectra of the composite support, which could beascribed to Si-O asymmetric stretching vibration. Thesevariationswere related to the interfacial interactions betweenthe two phases in the composite support based on thereference results in a MFI/MCM-41 system of Karlssonet al.39 The analysis results were similar to the observationsby Liu et al.40 and Fan et al.41

3.5.27Al MAS NMR.

27Al MAS NMR experimentswere carried out to study the effects of different compositemethods on the chemical environments of aluminum atomsin the corresponding samples, and the results are illustrated inFigure 6.The chemical shifts at about 58.624 and 1.362 ppm inspectra of zeolite USL were assigned to the tetrahedrally

coordinated framework and octahedrally coordinatedextra-framework Al species, respectively. There were twodistinct peaks with chemical shifts at 7.865 and 66.60 ppm,which were assigned to octahedral Al and tetrahedral Al,respectively. According to Lowensteins’ rule,42 Al-O-Allinkages in zeolitic frameworks were forbidden. As a result,all Al-O tetrahedral sites must be linked to four Si-Otetrahedral sites. Meanwhile, silica had a greater electrone-gativity than aluminum, so the chemical environments be-tween zeolite USL and alumina were different. The 27AlMAS NMR spectra results showed that these supportsobtained by two preparation methods were obviously domi-nated by signals in the range of 60-7.865 ppm, whichtypically represented the characteristics of the tetrahedrallycoordinated and octahedrally coordinated Al sites. More-over, a peak splitting with chemical shifts could be found ataround 60 ppm in Al2O3-USL-40(M), which was similar tothe peaks assigned to tetrahedral Al sites of zeolite USL andalumina, whereas there is no obvious peak splitting existed at60 ppm in Al2O3-USL-40(C).

Figure 5. FT-IR spectra of Al2O3 (a); zeolite USL (b); and Al2O3-USL composite supports (c).

Figure 6. 27Al MAS NMR of zeolite USL, Al2O3-USL-40(M),Al2O3-USL-40(M), and Al2O3.

Figure 7.NH3-TPD profiles of Al2O3-USL-x composite supports.

(39) Karlsson, A.; St€ocker,M.; Schmidt, R.MicroporousMesoporousMater. 1999, 27, 181–192.(40) Liu,H.T.; Bao,X. J.;Wei,W. S.; Shi,G.MicroporousMesoporous

Mater. 2003, 66, 117–125.(41) Fan, Y.; Lei, D.; Shi, G.; Bao, X. J.Catal. Today 2006, 114, 388–

396. (42) L€owenstein, W. Am. Mineral. 1954, 39, 92–96.

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Energy Fuels 2010, 24, 796–803 : DOI:10.1021/ef901098m Duan et al.

3.6. NH3-TPD. Acidic zeolites added to the alumina-supported CoMo and NiMo catalysts would be favorablefor the dealkylation and isomerization reactions of the alkylsubstituents, which might transform the refractory 4,6-DMDBT into more reactive species and thus should accel-erate HDS reactions.43-47

NH3-TPD patterns of the examined supports are pre-sented inFigure 7. The supports showed similar distributionsof the acid site strength in the range between 120 and 550 �C.The main peaks of ammonia desorption were located atabout 220 �C and a shoulder peak at 350 �C for all supports.When 10% of USL was introduced to Al2O3 the amountsof weak and moderate acid sites, which were sited at 120-220 �C, increased slightly, and it further increased withzeolite USL contents.Moreover, themaximal peak tempera-tures were also slightly increased with the introduction ofUSL and its content. The quantitative evaluations of weak(120-220 �C), moderate (220-350 �C), and strong (350-550 �C) acid sites based on Gaussian curve fittings arepresented in Table 3. It could be observed clearly that zeoliteUSL had moderate strength acid sites in all above cases.

3.7. H2-TPR. To investigate the types and the reducibilityof active metals existing in the catalyst precursors, TPRexperiments were performed over the oxide catalyst samples.The TPR profiles are given in Figure 8. On the basis of theTPR spectra ofW/Al2O3, a well-developed asymmetric peakcould be seen at 950 �C, which resembled those reported forW/Al2O3 catalysts.

36,48-50 This peak should be attributed to

the reduction of dispersed WO42- species of various reduc-

ibilities or probably small clusters of WO3 that were notdetected by XRD. However, TPR profiles of all NiWcatalysts also showed mainly two reduction peaks inthe temperature ranges of 600-700 �C and 700-1000 �C,respectively. Clearly, the high-temperature peak shiftedtoward lower temperature, indicating that some of the Wspecies were easier to be reduced by introducing Ni speciesto catalyst, which was in agreement with the results ofScheffer.49 Figure 8 shows that the peak shifts to lowertemperature direction followed the orders of W/Al2O3 <NiW/Al2O3<NiW/Al2O3-USL-10<NiW/Al2O3-USL-40,implying that W reducibilities also obeyed this order. That is,with the increase of zeolite USL contents, the locations of twointense peaks of NiW/Al2O3-USL-x catalysts shifted towardlower temperatures, demonstrating that the active metal oxidespecies had weaker interactions with the Al2O3-USL-x sup-ports than that with Al2O3 support. In brief, the incorporationof zeoliteUSLwouldbe beneficial to tuning themetal-supportinteractions, and resulted in easier reductions of metal oxidespecies. Similar findings were also reported by Solı́s et al.51

3.8. UV-vis DRS.TheUV-VisDRS analysis of the oxideprecursorwas performed to study the effects on coordinationof metal oxide species after the introduction of zeolite USL.The UV-Vis DRS spectra in the region from 200 to 800 nmare shown in Figure 9. It can be observed that bulk WO3

presented the characteristic behavior of WOx species inan extended three-dimensional crystalline network.52 Twoadsorption bands at 220-350 and 400-500 nmwere detected.The intense adsorption band at about 220-350 nm wasattributed to the ligand-metal charge transfer (LMCT): O2-

fW6þ inW-O-Wbridge bonds in polymeric structures.53,54

The band at around 250-280 nmwas assigned to tetrahedron

Table 3. Integrated Areas of Desorption Peak of Al2O3-USL Composite Supports in NH3-TPD Profiles

samples weak acid moderate acid strong acid total acid

USL 1.27 � 105 (46)a 1.33 � 105 (48) 1.51 � 104 (6) 2.76 � 105

Al2O3 3.44 � 104 (25) 4.21 � 104 (31) 6.12 � 104 (44) 1.38 � 105

Al2O3-USL-10 5.27 � 104 (29) 6.92 � 104 (39) 5.66 � 104 (32) 1.79 � 105

Al2O3-USL-40 7.16 � 104 (33) 1.01 � 105 (46) 4.57 � 104 (21) 2.18 � 105

aThe value in the parentheses is the percentage of various strength of acid.

Figure 8. TPR profiles of the supported NiW catalysts.Figure 9. UV-vis DRS spectra of bulk WO3, W/Al2O3, and NiW/Al2O3-USL-x catalysts.

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Energy Fuels 2010, 24, 796–803 : DOI:10.1021/ef901098m Duan et al.

or octahedron tungstenic species. The band at around280-340 nmwas ascribed to tungstenic oxide and octahedrontungstenic species. These octahedron tungstenic species weremore easy for the formation of coordinatively unsaturated orsulfur vacancies and thus should be favorable for hydrodesul-furization reaction.55,56 From the spectra in Figure 9, peaks at590 and 630 nm attributed to tetrahedrally coordinated Ni2þ

ions in NiAl2O4 were not found, which is consistent with theprevious research results.57-59 However, a new visible bandat around 420 nm, a typical characteristic of octahedrallycoordinated Ni2þ ions, shifted to higher wavelength with thezeolite USL content increasing, indicating that an enhancedincorporation of nickel with tungsten favored for producingNi-W-O species, the precursor of Ni-W-S active phases.

3.9.CatalyticActivity.Sulfur andnitrogen contents aswellas HDS and HDN efficiencies of diesel products over NiWseries catalysts are presented in Table 4 and Figure 10. Asshown in Table 4, compared with the commercial Al2O3(B),the Al2O3(P) prepared by the swing-pHmethod has a highercatalytic activity, this is due to the higher surface area, largerpore volume, and suitable pore diameter distribution of theAl2O3(P). So it is obvious that the textural properties werethe key point to affect the catalytic performance in the sametype of materials. Furthermore, the addition of zeolite USLto the catalyst support could improve the hydrotreatingperformances, and the assessment results indicated that thecatalyst of NiW/Al2O3-USL-10(C) with 10 m%USL in thesupport exhibited the highest HDS andHDN conversions of99.3 and 94.1%, respectively. Meanwhile, its relative cata-lytic activities of HDS and HDN were 2.32 and 1.36 timeshigher than those of the commercial catalyst of RN-10, andthey were also better than the corresponding catalyst ofNiW/Al2O3-USL-10(M) in which the support was preparedbymechanical mixingmethod. The higher catalytic activitiesof NiW/Al2O3-USL (C) catalysts might be caused bythe following reasons: (i) zeolites combined closely withalumina in the in situ prepared composite supports, whichmight be favorable for the cooperative effects of L and Bacid. (ii) From Table 4, compared with NiW/Al2O3-USL-(M) catalysts, the correspondingNiW/Al2O3-USL(C) had ahigher specific surface area, total pore volume, and averagepore diameter, which should be of benefit to the higherdispersion of active metals and to the diffusion of large

molecule like the sterically hindered alkyl-substituted DBTs,for example, 4,6-DMDBT.15,60,61 (iii) The combination ofzeolite USL with Al2O3 weakened the interaction betweenthe active metals and supports, and resulted in the higherreducibility of tungsten speices on the composite supports.Simultaneously, Ni-W-O active phase precursors wereeasy to be formed, whichwould be good for the enhancementof hydrotreating activity. Sulfur content of the optimal HDSproduct in Table 4 accorded with the sulfur regulation ofEuro IV specification (<15 μg 3 g

-1) of ultra clean diesel fuel.

4. Conclusions

In this study, two different ways were used to combinezeolite USLwith alumina for preparing a new type of supportfor hydrotreating catalyst. The physicochemical properties ofNiW/ Al2O3-USL catalysts and their supports were charac-terized by XRD, N2 physisorption, SEM, FT-IR, 27Al MASNMR, NH3-TPD, and UV-Vis DRS techniques etc. Theanalyzing results showed that the addition of zeolite USLcould adjust support acidity, and the zeolite USL-containingsupported catalysts reduced the interactionsbetween supportsand active metals, and thus it was beneficial to enhancing thereducibility of tungsten on composite supports, as well as itwas easy to formmore precursors ofNi-W-O active phases.

In comparison with the conventional support prepared bymechanical mixing method as Al2O3-USL-(M), the in situ

Table 4. Hydrotreating Activity Results of Diesel over Supported NiW Catalysts

series number catalysts S contents /μg 3 g-1 HDS (%) RVA(S) N contents (μg 3 g

-1) HDN (%) RVA(N)

feedstock 1290 9071 RN-10 39.75 96.9 100 71.25 92.1 1002 NiW/Al2O3(B)

a 12.10 99.06 199 55.19 93.29 1323 NiW/Al2O3(P)

b 9.82 99.3 223 65.90 92.7 1094 NiW/Al2O3-USL-5(C) 14.54 98.87 179 61.93 93.17 1165 NiW/Al2O3-USL-10(C) 9.10 99.3 232 53.34 94.1 1366 NiW/Al2O3-USL-20(C) 27.82 97.8 124 77.74 91.4 917 NiW/Al2O3-USL-30(C) 40.17 96.9 99 85.38 90.6 828 NiW/Al2O3-USL-40(C) 49.21 96.2 88 116.80 87.1 589 NiW/Al2O3-USL-10(M) 19.76 98.5 151 66.96 92.6 107

aThe commercial Al2O3 bought from Shandong. bAl2O3 prepared by the swing pH method.

Figure 10. Sulfur and nitrogen contents in hydrotreated dieselproducts obtained over catalysts containing zeolite USL. 1: RN-10; 2: NiW/Al2O3(B); 3: NiW/Al2O3(P); 4: NiW/Al2O3-USL-5(C); 5: NiW/Al2O3-USL-10(C); 6: NiW/Al2O3-USL-20(C); 7:NiW/Al2O3-USL-30(C); 8: NiW/Al2O3-USL-40(C); 9: NiW/Al2O3-USL-10(M).

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803

Energy Fuels 2010, 24, 796–803 : DOI:10.1021/ef901098m Duan et al.

composite method based on a modified pH-swing steps couldrealize the zeolite USL particles enwrapped by a film ofAl2O3

and thereby prepared a novel type of in situ Al2O3-USL-(C)composite supports. Al2O3-USL-(C)-supported NiW cata-lyst showed higher HDS and HDN activities than those ofAl2O3-USL-(M) catalyst, which mainly derived from thedifferent textural and surface properties of the catalysts. Theswing-pH method plays an important role in preparation ofthe Al2O3 support. The hydrotreating results indicatedthat the catalyst of NiW/Al2O3-USL-10(C) with 10 m%USL in the support exhibited the highest HDS and HDNconversions of 99.3 and 94.1%, respectively, all of which were

better than those on the commercial catalyst and NiW/Al2O3-USL-10(M) catalyst. NiW/γ-Al2O3(P) catalyst alsogave better performance for the HDS and HDN of diesel oil.Sulfur content of the optimal HDS product could meet thesulfur regulation of Euro IV specification of ultraclean dieselfuel.

Acknowledgment. The authors gratefully acknowledge thefinancial supports from National Natural Science Foundationof China (Nos. 20876173, 20773163, and 20833011), Ministryof Education key project of China, and CNPC-PetrochemicalResearch Institute project (No. 2008A-3801).