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Applied Catalysis A: General 281 (2005) 121–128

Catalytic hydrotreating of heavy gasoil FCC feed

on alumina–titania-supported NiMo catalysts

Vıctor Santesa,*, Javier Herberta, Maria Teresa Corteza, Rene Zaratea,Leonardo Dıaza, Prakash Narayana Swamyb, Mimoun Aouineb, Michel Vrinatb

aInstituto Mexicano del Petroleo, Eje Central Lazaro Cardenas 152, Col. San Bartolo Atepehuacan, C.P. 07730, Mexico, D.F., MexicobInstitut de Recherches sur la Catalyse, 2 Av. A. Einstein, 69626 Villeurbanne, Cedex, France

Received 22 June 2004; received in revised form 28 October 2004; accepted 14 November 2004

Available online 28 December 2004

Abstract

A series of NiMo/g-Al2O3–TiO2 catalysts were prepared and tested in the hydrotreating of heavy gasoil FCC feed in a pilot plant fixed-bed

reactor. Three different methods were applied to obtain the alumina–titania mixed oxides: impregnation of titanium butoxide over a g-Al2O3

support, co-precipitation of a mixture of aluminum sulfate, sodium aluminate and titanium sulfate, and a sol–gel method using alkoxides as

precursors; the titanium content was kept constant (5 wt.%). Additionally, a g-Al2O3 support was also prepared as a reference. All supports

were characterized by XRD, FT-IR pyridine and HRTEM. Catalysts were prepared by spraying at incipient wetness with the appropriate Ni–

Mo solution. Catalytic activity results (HDS, HDM and HDA) showed marked influence of the preparation method. This behaviour is

explained in terms of the differences in titania dispersion and acidity of the support.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Al2O3–TiO2; Acidity; XPS; HRTEM; Hydrotreating

1. Introduction

Hydroprocessing of gasoil has been requiring more

research to fulfill the regulations continuously tightened.

Since it is well known that the main contributor of sulfur to

the gasoline pool is the FCC gasoline, different approaches

have been applied to meet the environmental regulations. In

this context the pretreatment of FCC feed has shown to be an

excellent option not only to meet the new fuel specifications,

but also to improve fluid catalytic cracking unit (FCCU)

operation [1–3]. According to this approach the hydrotreat-

ing process can be designed to perform either in a two stages

reactor or in one reactor with two catalytic beds, the

selection of catalysts depending on the product objectives

and the feedstock properties [4–6]. Typical HDT catalysts

for FCC feed pretreatment consist of molybdenum

supported over alumina with either cobalt or nickel as

* Corresponding author. Tel.: +52 55 3003 8403; fax: +52 55 3003 8429.

E-mail address: vfsantes@yahoo.com (V. Santes).

0926-860X/$ – see front matter # 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.apcata.2004.11.025

promoter in which metal loading depends on the feedstock

properties. Improvements in catalysts performance can be

made by optimizing the support as well as active metals

dispersion. It is well known that a modification of the

support changes the interaction with active phase and

consequently the catalytic activity. In this regard, different

studies concerning various aspects of hydrotreating catalysts

on Al2O3–TiO2 have been undertaken by several groups

[7–13]. Furthermore, Zhaobin et al. [14] have reported that

modification of alumina by TiO2 improves not only the

hydrodesulfurization but also the hydrogenation reaction.

Recently, Pophal et al. [15] reported that alumina–titania

supported catalysts were more efficient for hydrodesulfur-

ization of 4,6-dimethyldibenzothiophene, which was attrib-

uted to the effect of prehydrogenation of a benzenic ring of

the alkyl-DBT derivatives. Since in practice the hydrotreat-

ing also involves the aromatics saturation and hydrodeme-

tallization reactions, it is important to consider studies

focused on these reactions. It is known that the HDM

reaction involves a sequence of steps including hydrogena-

V. Santes et al. / Applied Catalysis A: General 281 (2005) 121–128122

tion, dehydrogenation and cracking (C–C bond rupture) the

later reaction being catalyzed by proton of the catalyst

surface. This suggests that acidic supports may facilitate the

ring opening of hydrogenated intermediates, step involved

in the HDM mechanism, as recently proposed [16,17].

Since the amount of metals in heavy gasoil FCC feed is low

(1–3 ppm) the hydrodemetallization reaction of this type of

feedstock has received less attention, however, it is

important to mention that an increase in hydroprocessing

of heavy crudes such as Maya is now considered in Mexican

Refineries for the near future. These new feedstocks will

contain higher amounts of heteroatoms and metals, which

are responsible for the deactivation of the FCC catalyst.

More recently, Ancheyta and co-workers [18] have reported

the hydroprocessing of Maya crude oil using alumina–

titania supported catalysts. As part of our interest in

hydrotreating and the necessity of Mexican refineries to

process heavy oils such as Maya crude, which presents high

amount of heteroatoms and metals, we recently reported the

advantage of hydrotreating heavy gasoil FCC feed over

NiMo/g-Al2O3–TiO2 catalysts and operating at high LHSV

[19]. In continuation with our interest in the hydroproces-

sing of heavy gasoils we describe herein the effect of

preparation over acidity of various alumina–titania sup-

ported NiMo catalysts and the relationship with the HDT

activities in the hydroprocessing of a heavy gasoil FCC

feed.

2. Experimental

2.1. Preparation of the supports

The titania–alumina (5% Ti) supports (named SOP-A,

SOP-B and SOP-D) were prepared by three different

methods and a pure alumina support named SOP-C was also

synthesized. For SOP-A, alumina was first prepared by

extrusion of boehmite (Catapal B, Condea) to obtain 1/10 in.

diameter extrudates, which were annealed at 773 K; the

incorporation of titania was carried out by impregnation of a

solution of titanium butoxide/n-heptane in a glove box, then

it was maintained under room atmosphere overnight and

calcined at 773 K. SOP-B was prepared from sodium

aluminate, alumina sulfate and titanium sulfate salt

precursors. Solutions of aluminum sulfate and sodium

aluminate were mixed into a reactor vessel and heated at

343 K with continuous stirring for 30 min at pH of 7–8. A

solution of titanium sulfate was added; afterwards an

ammonium hydroxide solution was used to get a pH of 7–8

in the reaction mixture. Precipitated gel was heated for

30 min at 343 K. The slurry was filtered and washed three

times. The cake was dried at 383 K for 8 h and extruded to

obtain 1/10 in. diameter extrudates, which were kept at room

temperature overnight, dried at 393 K and calcined at 773 K

for 4 h. The preparation of the reference alumina support

(SOP-C) was similar to SOP-B using only aluminum sulfate

and sodium aluminate. Afterwards, the cake was extruded

and calcined under the aforementioned conditions. The

preparation of SOP-D was accomplished by hydrolysis of

aluminum sec-butoxide and titanium butoxide in 2-propanol

(Aldrich Co.). The hydrolysis proceeded at pH, 7, using an

alcohol to alkoxide ratio equal to 50, and water/alkoxide

ratio of 20. The extrudate support was obtained following

the methodology aforementioned. The thermal treatment of

the alumina (SOP-C) and alumina–titania (SOP-A, SOP-B

and SOP-D) extrudates supports was similar: they were

calcined at 773 K in the presence of air for 4 h.

2.2. Preparation of the catalysts

Supports were impregnated by spraying at incipient

wetness with a Ni–Mo solution. The salts used were nickel

hydroxycarbonate tetrahydrate 99.7 wt.% (Aldrich) and

MoO3 99.9 wt.% (Merck) as well as NH4OH 28 wt.%

(Aldrich). The proper solution concentration was deter-

mined by considering 6 wt.% of Mo (11 wt.% for CAT-A)

and 2.9 wt.% of Ni in the calcined oxidic catalyst. After

impregnation, samples were dried 2 h at 393 K and calcined

at 773 K for 4 h.

2.3. Physicochemical characterization of

supports and catalysts

2.3.1. Chemical analysis and textural properties

To determine the Ni, Mo and Ti contents in the annealed

samples, atomic absorption spectrophotometry (Perkin-

Elmer 5000 Spectrophotometer) was used. Textural proper-

ties of supports and catalysts were determined from the data

obtained by N2 physisorption at 77 K in ASAP-2000

Micromeritics equipment. Surface areas and pore size

distributions were calculated through BET and desorption

BJH methods, respectively.

2.3.2. Acidity measurements

Acidity of supports was examined by pyridine thermo-

desorption followed by IR spectroscopy on a Nicolet 60SX

FT-IR spectrometer. The samples were pressed into self-

supported wafers (ca. 5 mg cm�2, diameter = 1.6 cm) and

pretreated in situ in the IR cell. The activated catalysts were

equilibrated with 267 Pa of pyridine at room temperature

and evacuated at different temperatures.

2.3.3. X-ray photoelectron spectroscopy

XPS studies were recorded with a VG Scientific, Escalab

200 R spectrometer equipped with a hemispherical analyzer,

and using an Al Ka X-ray source. The scan speed was

0.02 eV/s with 0.01 eV step�1. The Al 2p line of Al2O3 at

74 eV was taken as reference in calculating binding energy

and accounting the charging effect. Experimental peaks

were decomposed using mixed Gaussian–Lorentzian func-

tions and a non linear least-square fitting algorithm. The

surface composition was determined from the integrated

V. Santes et al. / Applied Catalysis A: General 281 (2005) 121–128 123

Table 2

Physical properties of supports

Properties SOP-A SOP-B SOP-C SOP-D

Surface area (m2 g�1) 235 353 319 242

Total pore volume, N2 (cm3 g�1) 0.65 0.51 0.61 0.76

Average pore diameter, N2 (A) 68 47 48 77

Pore size distribution, N2 (A)

<50 22 42 39 18

50–100 70 43 20 69

100–200 7 6 10 11

300–500 1 6 14 1

>500 0 3 17 0

Table 3

Physical and chemical properties of catalysts

CAT-A CAT-B CAT-C CAT-D

Mo (wt.%) 9.52 6.10 6.3 6.2

Ni (wt.%) 2.42 2.70 2.46 2.7

Ti (wt.%) 5.69 4.99 - 4.62

Atomic ratio, Ni/(Ni + Mo) 0.29 0.42 0.43 0.42

Density (g cm�3) 0.82 0.79 0.65 0.58

Surface area (m2 g�1) 182 300 291 242

Total pore volume, N2 (cm3 g�1) 0.43 0.29 0.37 0.6

Average pore diameter, N2 (A) 69 40 47 76

peaks and using their respective experimental sensitivity

factors.

2.3.4. X-ray diffraction and HRTEM

Powder X-ray diffraction (XRD) was carried out on a

Siemens Model D-500 diffractometer with Cu Ka c-

radiation. High-resolution transmission electron microscopy

(HRTEM) was used to investigate the dispersion of titania on

alumina. Transmission electron microscopy examinations

were performed with a JEOL 2010 (200 kV) instrument

equipped with a LINK ISIS microanalysis system. The

resolution was 0.195 nm. All samples were ultrasonically

dispersed in ethanol at room temperature and the suspension

was collected over a carbon-coated grid.

2.3.5. Catalytic activity evaluation

The hydrotreating tests were carried out under steady-

state operation in a fixed bed pilot plant operating in down-

flow mode. The pilot reactor is made of a stainless steel tube;

the length and internal diameter of the reactor are 143 and

2.54 cm, respectively. The length reactor is divided into

three sections. The first section was packed with helly pack

and was used to heat up the mixture to desired reaction

temperature, the second contained the hydroprocessing

catalyst and the last one was also packed with helly pack.

The catalysts were in situ activated by sulfiding with

desulfurized naphtha contaminated with 0.6 wt.% CS2 for

12 h at 5.49 MPa, temperature of 503 K and LHSV = 3 h�1.

After completion of the catalyst sulfidation procedure,

the hydrocarbon stream was switched to the evaluation

feedstock. The reactor temperature was raised from that of

activation (503 K) to 603 K and a stabilization period until

no appreciable variations in temperature (2 h) was allowed.

All experiments were carried out at a constant reaction

pressure of 11.764 MPa, H2/oil ratio of 322 m3std/m3 and

LHSV of 6 h�1. Reaction temperature was studied at 603,

648 and 673 K and at each one several analysis were

performed in order to control the steady state achievement.

During the evaluations no appreciable deactivation was

observed which was monitored by check-back experiments

to the initial test temperature.

The properties of the gasoil used in the evaluations are

shown in Table 1. Total sulfur and nitrogen content in the

feedstock were determined by chemiluminescence (Antek-

7000). Aromatics content in feed and products was

measured by supercritical fluid chromatography (SFC).

Metals (Ni + V) were analyzed by ICP in a Perkin-Elmer

5000 M spectrometer.

Table 1

Physical and chemical properties of heavy gasoil FCC feed

Specific gravity (g cm�3) 0.912

Sulfur (wt.%) 2.84

Metals, Ni + V (wppm) 1.1

Aromatics (wt.%) 51.6

Total nitrogen, N (wppm) 1353

3. Results

3.1. Textural properties of supports and catalysts

BET specific surface area, total and average pore volume

of mixed oxide supports are given in Table 2. Results show

that the surface areas are higher for supports SOP-B and

SOP-C which were prepared from sulfate precursors.

Nevertheless, whatever the preparation, the surface area is

high and the pore size distribution indicates a mesoporosity

well-adapted for hydrotreating applications.

Fig. 1. XRD of supports: (a) SOP-A; (b) SOP-B; (c) SOP-D. (^) TiO2,

anatase; (&) g-Al2O.

V. Santes et al. / Applied Catalysis A: General 281 (2005) 121–128124

The results for the catalysts are presented in Table 3

which shows that the surface area and pore volume slightly

decreased as a result of the incorporation of active metals.

3.2. X-ray diffraction

The X-ray diffraction analyses of alumina–titania

supports: SOP-A, SOP-B and SOP-D showed marked

influence of the preparation method. For support SOP-A

intense signals corresponding to g-Al2O3 and TiO2 anatase

phase were observed (Fig. 1) whereas for support SOP-B

only g-Al2O3 was displayed and no peaks of titania were

detected. On the other hand, for the support SOP-D, which

was synthesized by sol–gel method, only the presence of

very poorly crystallized g-Al2O3 was detected and no trace

of anatase phase was found (Fig. 1).

Fig. 2. TEM micrograph of supports: (a

3.3. Transmission electron microscopy

More information about the dispersion of titania over

(in) the alumina matrix could be could be deduced from

HRTEM (S-TEM mode) characterizations. Fig. 2a shows

TEM image of sample A at a magnification of 4 00 000�. It

evidences a highly heterogeneous system in which

amorphous material Al2O3 is partly covered by large

crystalline TiO2 particles, in agreement with XRD analysis

which showed the presence of anatase. Such a visual

heterogeneity is confirmed by the EDX analysis since some

areas do not present any Ti though some other are rich in

this element due to relatively large TiO2 particles as can be

seen in Fig. 2a. For sample B, images at 4 00 000�(Fig. 2b) show a good homogeneity of the sample with a

high dispersion of spherical particles (3–5 nm diameter) of

) SOP-A; (b) SOP-B; (c) SOP-D.

V. Santes et al. / Applied Catalysis A: General 281 (2005) 121–128 125

Fig. 3. Infrared spectra of adsorbed pyridine over the supports, after

adsorption and desorption at room temperature, 423 and 523 K: (a)

SOP-A; (b) SOP-B; (c) SOP-D.

TiO2 as anatase phase, as observed from micro-diffraction.

The EDX analysis could not evidence any area without

titanium and the Ti/Al ratio is roughly the same whatever

the area analyzed, though higher than the bulk composi-

tion. Such a high dispersion of Ti accounts for the absence

of diffraction peak corresponding to TiO2 in the XRD

analysis of this sample.

For sample D, even if some few aggregates of TiO2

particles are still observed (Fig. 2c) and appeared in EDX

analysis as rich Ti-content areas, these aggregates are the result

of the agglomeration of small TiO2 particles and are mainly

associated with numerous and isolated small TiO2 crystallites.

However, it should be pointed that large particles of TiO2 as

those observed in sample A were never found.

3.4. Acidity measurements

Fig. 3 gives IR spectra after the adsorption of pyridine

at room temperature and after desorption at the same

Table 4

XPS Data for Sulfided NiMo/Al2O3–TiO2 catalysts

Catalysts Al 2p (eV) S 2p (eV) Mo 3d5/2 (eV) Ti 2p (eV) O 1s

CAT-A 74 161.7 228.6 458.7 530.9

CAT-B 74 161.7 228.5 458.7 530.8

temperature. For supports A, B and D bands at 1445, 1582

and 1615 cm�1 are representative of Lewis acidity.

However, bands at 1540 and 1539 cm�1 due to pyridinium

ions and characteristic of Brønsted acidity were not

observed. Spectra corresponding to desorption of pyridine

at 423 and 523 K are also reported in Fig. 3. For sample

SOP-A, the desorption was nearly completed at 523 K,

which is proof of a very low acidity of this support. On the

contrary, for samples B and D desorption at temperature

higher than 573 K (not given here) were necessary to remove

completely the adsorbed pyridine.

3.5. XPS results

In order to elucidate the state of molybdenum and nickel

species on supports, XPS analyses were performed on

samples A and B freshly sulfided and transferred into the

spectrometer using a ‘transfer box’ in order to avoid any air

contamination. The results are reported in Table 4. For both

catalysts the Mo 3d5/2 and S 2p binding energies are the

same and respectively equal to 228.6 � 0.1 and 161.7 eV

showing that the electronic state of the molybdenum is not

modified by the nature of the support, or not enough to be

evidenced by XPS. For sample B, the sulfur spectrum also

indicates some sulfate (BE of 169 eV). Moreover, the

electronic state of Ti is the same and corresponds to TiO2. As

regard to molybdenum, the decomposition of the Mo XPS

spectrum in three different oxidation states gives: Mo4+

corresponding to MoS2, Mo5+ belonging to Mo in an oxy-

sulfide phase and Mo6+ due to uncompleted sulfidation of the

precursor. Results given in Table 4 indicated a slightly

higher content of Mo6+ in sample B. It must be also noted the

slight shift of nickel binding energy toward lower value for

sample B, associated with a larger FWHM of the Ni 2p3/2

sulfide Ni peak, which suggests the presence of different Ni-

sulfided species due probably to the more difficult formation

of the NiMoS phase.

3.6. Catalytic activity

The removal of sulfur, metals and aromatics saturation as

function of the temperature are presented in Figs. 4–6,

respectively. These results of HDT activities clearly

demonstrate the interest in TiO2–Al2O3 supports since

higher conversions than that obtained with the pure alumina

supported catalyst are obtained on NiMo/TiO2–Al2O3

catalysts, whatever the reaction considered. Although all

samples have the same amounts of TiO2, results of

hydrotreating activity display significant differences.

(eV) Ni 2p3/2 (eV) Mo/Al Mo4+ (%) Mo5+ (%) Mo6+ (%)

854 0.081 83.4 10.2 6.4

853.6 0.049 80.4 10.5 9.1

V. Santes et al. / Applied Catalysis A: General 281 (2005) 121–128126

Fig. 4. HDS activity as a function of temperature.

Fig. 5. HDM activity as a function of temperature.

Fig. 6. HDA activity as a function of temperature.

It is seen in Fig. 4 that CAT-A displays the higher activity

for HDS and HDA reactions, which could be correlated

to its higher molybdenum loading. However, if CAT-B and

CAT-D showed no appreciable differences for the HDS

reaction, these catalysts displayed higher activities than

CAT-A for the reaction of hydrodemetallization. Moreover,

for about the same molybdenum content they present a better

activity for HDM and HDA than catalyst C prepared over the

pure alumina support. That will be discussed in relation with

physicochemical characterizations.

4. Discussion

The preparation of g-Al2O3–TiO2 supports by impreg-

nation, co-precipitation and sol–gel methods has shown to

afford solids with different chemical and textural properties.

For the TiO2–Al2O3 support prepared by hydrolysis of a

solution of titanium butoxide impregnated over alumina, the

XRD patterns given in Fig. 1 clearly evidence the formation

of anatase crystallites, proof of a poor dispersion of Ti.

Compared to the previous work of Stranick et al. [20], this

result is disappointing since, using titanium isopropoxide as

precursor; these authors were able to prepare Ti well-

dispersed over Al2O3 for titanium-content up to 14 wt.%.

That could be due to different interaction of the precursor

with the support. High dispersions have been also reported

by McVicker and Ziemik [21] for TiCl4-impregnated

alumina.

The two other precipitation methods studied, the co-

precipitation of aluminium salts and titanium sulfate by

ammonium hydroxide solution, and the use of alkoxides, led

both two samples which are devoid of any TiO2 diffraction

lines. This result indicates that TiO2 is present in aggregates

with crystallized entities probably less than 1.0 nm in

diameter. These techniques offer the potential of providing

well homogeneously dispersed TiO2 over and inside the

alumina matrix. Indeed TEM analysis confirmed the

presence of relatively large TiO2 particles in support A,

though the crystallites of anatase observed on supports B and

D are very small even if slightly more agglomerated over the

latter than over the former.

As regard to the hydrotreating reactions, for the same

molybdenum content, catalysts prepared over mixed oxides

(CAT-B and CAT-D) present higher catalytic activities than

the pure alumina-supported sample (CAT-C), which con-

firms the interest of such materials. However, effect of the

nature of the support over the catalytic activity of sulfides is

still debated, and effect of titania is deeply controversial

[21,22]. Nevertheless in this study, results of acidity

measurement by FT-IR of pyridine shows that supports B

and D present higher Lewis acidity than pure alumina and

therefore lead us to conclude about some positive effect of

this acidity. Recently, Mauge et al. [23] compared a series of

NiMo catalysts prepared over silica–alumina presenting

various acidity in hydrogenation of toluene and concluded

that the support acidity could not only modified the number

of catalytic sites (CUS: coordinatively unsaturated sites), but

could also increase the ‘quality’ of the sites. Therefore a

direct correlation seems to exist between the Ti dispersion

and the acidity and consequently with the increase of activity

in HDS and HDA reactions, which we believe to be

performed over the same sites [24].

Such a correlation between acid–base properties of the

catalyst and activities has been recently reported by Zuo

[25]. The authors compared a series of NiW/Al2O3 catalysts

prepared with the same tungsten content but variable Ni/W

ratios in HDS, HDA and isomerization reactions. Paralle-

lism between the promoter content (which affect the acidity

of the sulfide phase) and activities in the three reactions led

to conclude in a common factor due to an increase in

hydrogen activation.

V. Santes et al. / Applied Catalysis A: General 281 (2005) 121–128 127

For support SOP-B the origin of such a variation of

acidity could be however discussed. This support has been

prepared using sulfate and it is well-known that the Lewis

acidity could be increased by addition of sulfate ions [26],

which ones are still present in the final solid as evidenced by

XPS study (peak at binding energy of 169 eV). Therefore, a

new support has been prepared by the sol–gel method (SOP-

D) and the support derived showed about the same acidity

and even slightly better as suggested later with the HDM

activities. These results suggest that acidity of supports B

and D is not the result of the presence of sulfate ions but

more probably of the effect of the mixed oxide.

If a better Ti dispersion leads to higher acidity, as

concluded from acidity measurements, it has been also

reported that such a variation of acidity of the support could

unfortunately also induce a lower formation of the mixed

phase [27]. Indeed, XPS experiments evidenced such a

variation since the binding energy of nickel appears slightly

lower over catalyst CAT-B than over CAT-A. Positive effect

of titania as additive of the support, probably by increasing

hydrogen activation appears to be more important than the

possible inhibition in the mixed phase formation.

Following the work of Lacroix and co-workers [28,29] it

is now well-admitted that hydrogen activation over sulfide

catalysts proceeds via an heterolytic dissociation leading to

proton and hydride. Therefore, a positive effect of titania on

hydrogen activation must be reflected in a reaction involving

such entities. That is the case of hydrogenation of an

aromatic ring in which the rate determining step has been

reported to be the addition of hydride [30]; it must be also the

case of the hydrodemetallization reaction. According to

Janssens et al. [17] the HDM of metalloporphyrin proceeds

via three hydrogenation steps on b-pyrrole positions of the

porphyrinic structure leading to a meso-bridge-hydroge-

nated structure which is followed by an acid attack, ring

opening and elimination of a tolyl group before metal

removal. Thus, an increase of the H+ entities will lead to a

better HDM. That is effectively the case for titania–alumina

support and more specifically for catalysts CAT-B and

CAT-D prepared over support in which exists a close contact

between TiO2 and Al2O3.

In this regard it has been reported that alumina modified

by titania can improve not only the hydrodesulfurization but

also the hydrogenation reaction [9,14,15]. Accordingly, both

hydrogenation steps and acid attack of the HDM mechanism

could be promoted and that easily explains the higher HDM

activities observed over these new catalysts. Finally, the

slight difference between CAT-B and CAT-D in the HDM

reaction could be explained by textural variations between

both supports. Results of Table 2 show that the co-

precipitation method gives the highest surface area, whereas

the pore volume and porosity distribution are slightly

lower. On the other hand, the sol–gel method showed better

pore distribution in the range of mesopores and higher

pore volume, which would facilitate the diffusion of the

metalloporphyrines.

Therefore, the acidity and dispersion of Ti in SOP-B and

SOP-D seem to be important in the performance of CAT-B

and CAT-D toward the reactions of HDM and aromatics

saturation, even though they have lower Mo loading.

5. Conclusion

The present work demonstrates the interest of titania as

additive of alumina support for hydrotreating catalysts. Only

5 wt.% of Ti is enough to increase the activities in HDS,

HDA, and HDM reactions, as compared with a NiMo/Al2O3

catalyst.

Such a gain of activity deeply depends on the method of

preparation of the support, in order to get a close contact

between TiO2 and Al2O3, leading therefore to an increase of

the acidity of the support. Such a variation appears to

promote the heterolytic dissociation of hydrogen, leading to

more H� species involved in the hydrogenation steps and

more protons involved in the acid attack step of the HDM

mechanism.

Acknowledgement

The authors thank Instituto Mexicano del Petroleo for its

financial support.

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