HYDRODESULFURIZATION OF THIOPHENE OVER BIMETALLIC ...

HYDRODESULFURIZATION OF THIOPHENE OVER 

BIMETALLIC Ni–Mo SULFIDE CATALYSTS PREPARED 

BY DIFFERENT METHODS 

Hamid A. Al-Megren* 

Petroleum and Petrochemicals Research Institute, King Abdulaziz City for Science and 

Technology, P.O. Box 6086 Riyadh 11442, Saudi Arabia 

Hamid A. Al-Megren 

: ةـصلاخلا 

ة��يكيناكيملا (IMPR) بير��شتلا ق��يرط ةطا��سوب ند��عملا يئا��نث Ni–MO/Al2O3 د��يتيربك ن��م تاز ّ◌ّـ��فحم ري��ضحت - ث��حبلا اذ��ھ ي��ف - م��ت د��قل 

ةع�شأ فار�حناو ،نيجورتينلا�ب يئا�يزيفلا زاز�تملاا ةطا�سوب تاز�فحملا صاو�خ د�يدحت ﱠمت امك . (OMXC) ةيوضعلا Matrix قرـح ةقيرطو (MECH) 

ت�يربكلا عزن ةيلمع يف اھتيلاعف ةساردو ةرضحملا تازفحملل ةترْبَك ةيلمع تيرجأ دقو . نامار فايطمو ينورتكللإا سجملا ةطاسوب قيقدلا ليلحتلاو 

سكإ 

ة��يلاعف ر�ثكأ (OMXC) ة��قيرطب هري�ضحت م��ت يذ�لا ز��فحملا نأ�ب د��جُو د�قو . م٣٥٠ 

ةرار��ح ة�جردو د��حاو يو�ج طغ��ض ت�حت نيفو��يثلل (HDS) ة�جردھلاب 

. IMPR و MECH قرطب ةرضحملا تازفحملا عم ةنراقم % ٥٧ يلاوحب 

ABSTRACT 

Bimetallic Ni–Mo sulfide Al2O3 catalysts were prepared by impregnation (IMPR), mechanical (MECH) and 

organic matrix combustion (OMXC) methods. The prepared catalysts were characterized by nitrogen physisorption, 

X-ray diffraction, electron probe microanalysis, and Raman Spectroscopy. The samples were sulfided and their 

activity in hydrodesulfurization (HDS) of thiophenes at a pressure of 1 atm and a temperature of 350ºC was tested. It 

was found with Ni–Mo that the catalyst prepared by the OMXC method is more active (by upto 57%) as compared 

with the corresponding catalysts prepared by (MECH) and conventional impregnation methods. 

Key words: bimetallic HDS catalyst, preparation, characterization 

* E-mail: almegren@kacst.edu.sa 

Paper Received: 17 November 2007; Accepted 12 November 2008 

The Arabian Journal for Science and Engineering, Volume 34, Number 1A January 2009 55

56 


HYDRODESULFURIZATION OF THIOPHENE OVER BIMETALLIC Ni–Mo SULFIDE 

CATALYSTS PREPARED BY DIFFERENT METHODS 

1. INTRODUCTION 

At present, the hydrodesulfurization (HDS) process is an efficient method for sulfur removal from gasoline and 

diesel of high sulfur content [1,2]. In the HDS process, organic sulfur compounds in the liquid fuels are broken 

down to H2S using NiMo–CoMo/Al2O3 catalysts [3–6], followed by the removal of H2S, and the sulfur content in 

fuels can be reduced to about 10 ppm. Sulfided Ni–Mo catalysts are widely used in hydrotreating reactions [7,8]. 

Several studies have shown that monometallic cobalt catalyst are active for hydrodesulfurization (HDS) reactions 

[9–11]. For example, Duchet et al. investigated carbon supported molybdenum and tungsten catalysts for HDS of 

thiophenes [12]. In some cases, however, their HDS activities are low and unimportant due to a low degree of cobalt 

dispersion and/or strong interactions with some support materials like alumina [13]. Therefore it is of great interest 

to examine the influence of the preparation method on the properties and activity of the catalyst, as well as on the 

interaction between promoters and supports [14]. In the present investigations, emphasis was focused on studying 

the effect of the preparation method on the hydrodesulfurization activity of Ni–Mo catalysts. 

To improve the performance of the HDS catalyst, all steps in the preparation procedure should be considered. 

The key parameters are the choice of a precursor of the active species, support, synthesis, and post-treatment of the 

synthesized catalyst. The nature of the active phase can be modified by changing the amount of active component 

[15], and by the introduction of additives. Numerous additives have been studied, and phosphorus [16, 17] and 

fluorine [18–21] have received special attention. In some studies, the sulfides of transition metals were replaced by 

nitrides [22] or carbides [23, 24]. Noble metals are also used as the active phase in hydrotreating catalysts for second 

stage HDS [25]. 

Various supports have been used to enhance the catalytic activity in HDS: carbon [26–28], silica [29, 30], 

zeolites [31–34], titania and zirconia [35–37], and silica–alumina [38, 39]. Combining new types of catalytic species 

with advanced catalyst supports such as ASA (amorphous silica–alumina) can result in an extremely high 

desulfurization performance. The application of ASA-supported noble metal-based catalysts for the second-stage 

deep desulfurization of gas oil is an example [25]. The Pt and Pt–Pd catalysts are very active in the deep HDS of prehydrotreated 

straight run gas oil under industrial conditions. These catalysts are able to reduce the sulfur content to 6 

ppm, while simultaneously reducing the aromatics to 75% of their initial amount. At high sulfur levels, the ASA 

supported noble metal catalysts are poisoned by sulfur and Ni–W–ASA catalysts become preferable for deep HDS 

and dearomatization. 

It has long been recognized that the optimal performance of a catalyst depends on its preparation method [40]. 

The common preparation methods require a combination of different unit operations. Some of these are not entirely 

understood. They can be described as: (i) introduction of the metal precursor on the support by impregnation or ionexchange 

[41], co-precipitation and deposition precipitation [42]; (ii) drying and calcination, and (iii) reduction. The 

size and distribution of metal crystallites in the support, the homogeneity of the multi-component catalyst, the 

porosity, surface area, and pore size distribution are all functions of the precursors used in the preparation. Some 

preparation parameters such as temperature of treatment, pH of the solution and the aqueous or organic medium also 

contribute to the catalyst preparation. Recently, significant progress has been made towards understanding the 

relationship between the preparation method and final properties of the catalyst and supports [41]. Generally, it is 

believed that the catalyst selectivity depends on the particle size of the dispersed metal and spatial distribution of the 

active component in the porous support. The stability of the catalyst depends on the interaction of the metal and the 

supports. 

The controlled preparation of heterogeneous catalysts has been studied for more than 100 years [42]. However, 

perfectly designed catalysts still remain a challenge. Impregnation, sol–gel, ion-exchange, precipitation, and 

deposition-precipitation are the commonly used methods [43]. 

The impregnation method requires the support to be contacted with a certain amount of solution of a metal 

precursor, usually a salt, and then it is aged, usually for a short time, dried, and calcined [41]. This method appears to 

be simple, and economical (especially when using solutions of costly active components), and able to yield a 

reproducible catalyst. However, when drying, the dissolved metal compounds often crystallize in the support, which 

leads to larger crystallites and thus leading to low metal dispersion. 

The ion–exchange method consists of exchanging either hydroxyl groups or protons from the supports, with 

cations and anions in the solutions [41]. In this method, it is important to adjust the pH values to control the 

interaction between the support and metal precursors. A knowledge of the isoelectric point is essential if meaningful 

dispersions are to be obtained. 

January 2009 The Arabian Journal for Science and Engineering, Volume 34, Number 1A


The sol–gel method is the latest technique for catalyst preparation, in which the metal–organic precursors are 

mixed with metal precursor to form a homogeneous solution [43]. The solution is passed through the hydrolysis and 

polymerization process by adding water while carefully controlling the pH and reaction temperature. This results in 

the formation of colloidal particles and micelles of approximately 10 nm diameter. These particles continue to 

increase in size until a metal oxide gel is formed. 

However, each of these techniques is either difficult to control or the preparation process is complex and difficult 

to use on an industrial scale. Also, none of them ever takes into consideration the adjustment of the interaction 

between the active metal and support, which is regarded as one of the properties of supported catalysts. 

Also, for hydrotreating catalyst preparation, the content and particle sizes of the active components such as Mo or 

W are crucial for the catalyst performance. No methods are available to load the high content of the Mo or W needed 

with desirable particle size. Hence, selective deep removal HDS now needs noble metal catalysts, which are much 

more costly and easy to deactivate. 

Recently, a new catalyst preparation method, i.e. organic matrix combustion (OMXC) has been developed [44, 

45]. Some organic compounds are mixed with soluble metal compounds to form a homogeneous solution with 

addition of minimum water (or other solvent) where necessary. The particle size of the catalyst is controlled by the 

ratio of the organic compounds to the metal in the solution. Interaction between the active component and support is 

controlled by the calcinations temperature and atmosphere. 

The aim of this work is to develop more robust catalysts with high activity for selective removal of sulfur from 

thiophene, to hydrogenate the C–S bond; and with low ability to hydrogenate the mono C=C bonds. The key to 

achieving this goal is to control the distribution and particle size of the active component, e.g. MoS2, and optimize 

the promotion of Ni and Mo in the catalysts supported over alumina. Active component precursors will be chosen 

from the ammonium salts. This catalyst will be prepared and compared by three different preparation methods. 

2. EXPERIMENTAL 

2.1. Catalyst Preparation 

In this work, 15% Ni–Mo bimetallic material supported over alumina was prepared using three different 

methods: impregnation (IMPR), mechanical (MECH), and organic matrix combustion (OMXC). All catalysts were 

prepared in oxide phase then sulfurized using a stream of hydrogen saturated by thiophene at room temperature. 

Nickel nitrate hexahydrate Ni(NO3)2.6H2O(99.0% Fluka) was mechanically mixed with molybdenum trioxide at 

a Ni/Mo atomic ratio of 0.43. An amount of 15% from the mixture was added to alumina (150 mesh, 150 m 2 g -1 , from 

Aldrich). The mixture was dried in a vacuum oven at 120ºC and calcined at 550ºC for 15 hours. The resulted powder 

sample was named as MECH. 

Nickel nitrate hexahydrate was dissolved in small amount of water, mixed with ammonium 

heptamolybdatetetrahydrate (NH4)6Mo7O24-4H2O (99% Riedel-de Haën) then impregnated with alumina. The 

mixture was dried in a vacuum oven and calcined at 550ºC for 15 hours. The resulted powder sample was named as 

IMPR. 

The same ratio of Ni/Mo supported over alumina was prepared using OMXC method by mixing calculated 

amount of urea (Fisher Chemicals) with ammonium heptamolybdate-tetrahydrate and nickel nitrate hexahydrate 

(Ca.1g/2ml = (Ni- and Mo-Precursors+urea)/ water ratio. This mixture was stirred to form a homogeneous slurry, 

then mixed with Al2O3 support and heated at 50ºC for 2-3 hours to obtain urea-based slurry containing molybdenum 

fully loaded over alumina. This paste is ignited at 500ºC in static air for 10 min. The resulted powder sample was 

named as OMXC. 

2.2. Catalytic Tests 

All catalysts were activated by sulfurization using 20 ml of hydrogen through a jacketed saturator containing 

thiophene (10.9 kPa). The flow of hydrogen with thiophene passed through 200mg of catalyst placed in a fixed bed 

reactor and heated at 5ºC/min to maximum temperature 450ºC, and was then held at this temperature for 3 hours. 

The catalytic behavior tests of the prepared supported catalysts (MECH, IMPR, and OMXC) for the 

hydrodesulfurization of thiophene were carried out in a laboratory bench scale pilot plant fitted with mass flow 

meters and a fixed bed down-pass flow quartz reactor placed in a cylindrical furnace, equipped with a coaxial 

thermocouple. The inner diameter for the reactor was 4 mm and its length 300 mm. The catalyst zone in the middle 

of the reactor had a length of 30 mm and was filled with 200 mg of catalyst diluted with an equal amount of quartz 

particles (50 – 100 mesh) in order to minimize temperature gradients. In the center of the catalyst bed, a 

thermocouple was installed in contact with the catalyst particles to measure the reaction temperature. The heating 

zones at the inlet and the outlet of the reactor were measured by a thermocouple located inside the furnace and were 

controlled by a temperature controller (Cole Parmer Digi-Science). 


58 


Normally, the flow rate of hydrogen was 20 ml/min at atmospheric pressure. The activity of nickel–molybdenum 

supported catalysts (MECH, IMPR, and OMXC), and thiosophene conversion were studied at a temperature of 

350°C 

Blank reactor runs were conducted as described above in the absence of catalysts. No significant conversions of 

thiophenes were observed under the conditions of each experiment. Carbon mass balancing closed within 8%, most 

within 5%. 

2.2.1. Gas Chromatography 

The analysis of the reaction mixture was carried out using, a Hewlett–Packard 5890 series II. The instrument 

equipped with 1 × 1/8" O.D. stainless steel packed column (80 – 100 mesh range Porpak S); and flame ionization 

detector (FI), and thermal conductivity detector (TCD). 

The instrument was calibrated by external standardization method using standard mixture of (CH4, C2H6, C2H4, 

C3H8, C3H6, C4H10, C4H8, and C4H8). 

2.3. Catalyst Characterization 

Electron probe micro-analyzer (EPMA) (JEOL JXA-8900R/RL) was used for identification of constituent 

elements in the prepared samples and to study the elements distribution over the support. Analysis was performed 

by illuminating the sample surface with a finely focused electron beam and measuring the wavelengths and 

intensities of characteristic X-rays from the specimen and the quantities of secondary electrons and backscattered 

electrons from it. 

The X-ray diffraction (XRD) was carried out in Philips PW1710 diffractometer with CuKα radiation. The data 

were collected at room temperature, in θ/θ reflection mode, scanning the specimen between 3º–70º in 2θ, using steps 

of 0.05º, with a time per step of 1.25 s. 

The structure of the samples was studied using laser Raman spectroscopy from a Jobin Yvon Labram 

spectrometer with a 632.8 nm HeNe laser, run in a back-scattered confocal arrangement. The samples were pressed 

in a microscope slide; the scanning time was set to 30s. Raman spectra were recorded in air at room temperature 

with a resolution of 2 cm –1 and a scanning range of 100 to 2500 cm –1 . 

2.3.1. Physisorption 

Nitrogen adsorption–desorption isotherm of MECH, IMPR, and OMXC catalyst samples were measured on a 

Micromeretics ASAP2010 system using nitrogen sorption at 77K. Prior to the experiments, approximately 0.2 g of 

sample was degassed at 523K for 16h. The surface areas were calculated using a multipoint Brunauer–Emmett– 

Teller (BET) model. The pore size distribution was obtained using BJH and BET models and the total pore volumes 

were estimated at a relative pressure of 0.99 atm, assuming full surface saturation with nitrogen. 

For characterization purpose, samples of the fresh and used catalyst were passivated at room temperature in flow 

of 1% O2/He before they were exposed to air. 

3. RESULTS AND DISCUSSION 

The surface area measurements for the three prepared bimetallic catalyst samples (MECH, IMPR, and OMXC) in 

oxide phase, before sulfurization, are shown in Table 1. The surface areas for the samples increase in following 

order: MECH (125.5 m 2 /g) > OMXC (122.5 m 2 /g) > IMPR (119.3 m 2 /g); the differences are relatively small. The 

highest surface area for the sample prepared by mechanical method could be attributed to less dispersion between the 

active component and surface of the support. In Table 1, the average pore diameter and the total volume, measured 

for the three samples, were the highest for the samples prepared by mechanical and the lowest for the sample 

prepared by combustion method. The particle size distribution analysis shows that the samples prepared by IMPR 

and OMXC have almost similar size (~60μm), much higher than the particle size for sample prepared by MECH 

(~27μm). 

Table 1. Physical Properties of NiMoOx Catalyst Prepared by Impregnation, Mechanical, and Organic Matrix 

Methods 

Preparation Surface 

Method Area m 2 g -1 

Total Pore Volume 

Cm 3 g -1 

Average Pore Particle Size 

Diameter A º Distribution μm 

IMPR 119.27 0.16529 55.436 59.81 

OMXC 122.50 0.16420 53.617 63.53 

MECH 125.51 0.18621 59.343 26.81 


Count/arb, units 

500 

400 

300 

200 

100 


0 

0 10 20 30 40 50 60 70 

2 q 

Figure 1. XRD pattern for Ni3Mo7Ox/Al2O3 catalysts prepared by Impregnation, Mechanical and OMXC methods 

The Arabian Journal for Science and Engineering, Volume 34, Number 1A January 2009 59 

Al 

Al 

Al 

Al 

Al 

OMXC 

Al 

The X-ray diffraction patterns for the three samples in oxide phase are shown in Figure 1. Sample MECH shows 

an appearance of MoO3 peaks at 2θ values of 14.4, 23.6, and 26.8º. Sample IMPR also shows slight appearance of 

MoO3 peak at 2θ values of 23.6º, while there is no appearance of these peaks on the sample prepared by OMXC 

method. These appearances of the MoO3 peaks suggest that both methods, mechanical and impregnation, lead to 

lower dispersion of the active component compared to OMXC method, which enables a high dispersion of 

Ni3Mo7Ox. 

Raman spectroscopy is a powerful tool to study the structure of catalytically active phases on a support. Typical 

support such as alumina shows weak Raman scatters, with consequence that adsorbed species can be measured at 

frequencies as low as 50 cm –1 [10]. Figures 2, 4, and 8 show the Raman spectra of the oxides and sulfided phase for 

the catalysts in the 200–2000 cm –1 range. The spectra of Ni3Mo7Ox/Al2O3 catalysts do not exhibit the features of 

Ni3Mo7Sx/Al2O3 catalysts. The Raman spectra of NiMoOx/Al2O3 bimetallic supported oxide samples prepared using 

the three methods are shown in Figure 2. It shows that the main phase on the surface of samples IMPR and MECH 

is MoO3. The Raman band on these samples at 995 cm –1 corresponds to the stretching mode of Mo=O, and the band 

at 830 cm –1 corresponds to the anti-symmetric stretching mode of Mo–O–Mo, and the band at 295 cm –1 corresponds 

to the bending mode of Mo=O in the polycrystalline MoO3. The strong band at 965 cm –1 on sample MECH is due to 

the A1 mode of Mo=O in the MoO4 tetrahedral units. The broad band for samples IMPR and OMXC at 955 cm –1 , 

which can be unfolded into two peaks at 955 and 965 cm –1 , highlights the band characteristic of NiMoO4. The 

Raman results suggest that the main oxide present clearly on the surface of sample MECH and IMPR is MoO3. Our 

findings agree with those reported by Sergio et al. [46, 47]. In addition, the shoulder of 950 cm –1 and the weak 

Raman bands at about 825 cm –1 are associated with the Mo–O–Mo for the polymolybdate species [48–51]. On the 

other hand, the weak intensity band at 950 cm –1 is characteristic of Ni–Mo oxide. 

Ramman Pand Intincety 

4500 

4000 

3500 

3000 

2500 

2000 

1500 

1000 

500 

MECH 

OMXC 

I MPR 

Al 

MECH 

I MPR 

0 

0 500 1000 1500 2000 

Ramman Shift, cm -1 

Figure 2. Laser Raman spectra for Ni 3Mo 7O x/Al 2O 3 catalysts prepared by Impregnation, Mechanical and OMXC methods

60 


Figure 3 shows the X-ray diffraction patterns for the three samples after the sulfidation reaction. It is clear that 

the main peaks for the oxide phase, i.e. MoO3 at 2θ values 14.4, 23.6, and 26.8, have disappeared from IMPR and 

OMXC samples while they have weakened on the MECH sample. This disappearance was attributed to the higher 

formation of sulfide phase on IMPR and OMXC, while some oxides still remain on MECH sample. Our results 

agreed with those reported by some investigators [48]. They have shown that during the primary period of 

thiophenes hydrodesulfurization on MoO3, a definite amount of sulfur was consumed by sulfidation of the oxide. 

This means that oxidic molybdenum catalyst can be sulfided by thiophenes, or by the hydrogen sulfide produced by 

DHO of thiophenes. 

Count/unit 

400 

300 

200 

100 

0 

10 20 30 40 50 60 70 

January 2009 The Arabian Journal for Science and Engineering, Volume 34, Number 1A 

2 q 

MECH 

OMXC 

I MPR 

Figure 3. XRD pattern for Ni 3Mo 7S x/Al 2O 3 catalysts prepared by Impregnation, Mechanical and OMXC methods 

The laser Raman spectra of the three samples (IMPR, MECH, and OMXC) after converting them from oxide to 

sulfide phase by sulfurization reaction are shown in Figure 4. The spectrum intensity of oxide phase (Figure 2) was 

highly reduced after sulfurization reaction. The vibration frequency at band 965 cm –1 Mo=O in the MoO4 tetrahedral 

units is strongly reduced after sulfurization. This band, i.e. 965 cm –1 disappeared completely on OMXC sample but it 

was partially reduced on rest of the samples. This result suggests that the molecular symmetry mode in the surface of 

MoO3 was changed after sulfurization [46–47]. In addition the spectrum of Figure 4 shows two bands at about 440 

and 450 cm –1 which could be attributed to MoS2 structure [13] 

1000 

Raman band intensity / Arb. units 

800 

600 

400 

200 

0 

MECH 

OMXC 

IMPR 

500 1000 1500 2000 

Raman shift, cm -1 

Figure 4. Laser Raman spectra for Ni 3Mo 7S x/Al 2O 3 catalysts prepared by Impregnation, Mechanical and OMXC methods


In the present study, the catalytic activity of sulfided NiMo/Al2O3 catalysts (IMPR, OMXC, MECH) were 

examined in the hydrodesulfurization of thiophenes at a temperature of 350°C and under atmospheric pressure. The 

conversion of thiophenes is shown in Figure 5. It can be observed that thiophenes conversion is constant over about 

8 h time on stream. Thus, high catalytic activity (57% of thiophenes conversion) is reached for the catalyst OMXC. 

Catalytic activities of IMPR and MECH catalysts are lower (45% and 21% of thiophene conversion respectively). 

The rate of reactions also show in order 73.80, 58.16, and 26.05 µmol (g min) –1 for OMXC, IMPR, and MECH 

respectively. The superior activity of OMXC catalyst is attributed to the incorporation of Ni–Mo onto the support 

surface. This provides a stronger metal–support interaction allowing a better dispersion of nickel and molybdenum 

oxidic and sulfided phases. On the other hand, too strong metal–support interaction makes the reduction and 

sulfidation of Ni and Mo species more difficult. 

Conversion, % 

60 

50 

40 

30 

20 

10 

OMXC 

0 

0 1 2 3 4 5 6 7 8 

Time, hour 


IMPR 

MECH 

Figure 5. HDS of thiophene over Ni 3Mo 7S x/Al 2O 3 catalysts at 350ºC, atmospheric pressure and 20ml/min flow of hydrogen 

This is in agreement with the results of Klimova et al. [53] who found NiMo catalysts supported on Al-SBA-16, 

prepared by grafting with AlCl3, show high activity in HDS of 4,6-DMDBT which attributed a good dispersion of Ni 

and Mo active phases. 

The catalytic activity for these catalysts was tested on hydrodesulfurization of thiophene at 350 o C and 

atmospheric pressure. Figure 5 shows that OMXC catalyst has superior activity (57%) compared to IMPR (45%) and 

MECH (21%) catalysts after seven hour of the reaction time. The rates of reaction also show in order 73.80, 58.16, 

and 26.05 umol (g min) –1 for OMXC, IMPR, and MECH respectively. This superior activity for OMXC sample 

attributed to the well dispersion of Ni–Mo over alumina as well as the higher sulfide formation compare to IMPR 

and MECH [46]. 

= Ratio 

C 4 /C 4 

2.6 

2.5 

2.4 

2.3 

2.2 

2.1 

IMPR 

MECH 

OMXC 

2.0 

0 1 2 3 4 5 6 7 8 

Time, hour 

Figure 6. C4/C4= mol ratio for HDS of Thiophene over Ni3Mo7Sx/Al2O3 catalysts at 350ºC, atmospheric pressure and 20ml/min 

flow of hydrogen.

62 


Figure 6 shows the ratios of butane and butenes (C4/C4 = ), which are produced from HDS of thiophene reaction. 

The OMXC catalyst yielded the highest content of olefins, as compared to the IMPR catalyst. Products distribution 

data provide some insight into the possible pathway of thiophene desulfurization, which is difficult to extract from 

similar catalysts in which products are substantially altered by high rates of hydrogenation and isomerization 

reactions. 

More important are the differences between the three catalysts (IMPR, MECH, and OMXC) when we consider 

the product distributions. GC analysis showed the formation of mainly C4 and C4 = fractions, but it has not showed 

the formation of tetrahydrothiophene and butadiene. However many authors have argued for the preferential direct 

desulfurization route, by the absence of tetrahydrothiophene [50]. 

Therefore our result shows that the pathway of reaction is the direct hydrodesulfurization route with successive 

hydrogenation, as shown in Scheme 1. 

S 

HDS 

HD 

S 

HD 

HDS 

HD 

HDS 

Scheme 1 

With the three catalysts, the ratio of C4 to C4 = is around 2.5. 

This suggests butane generation by hydrogenation of C4 compounds. These compounds are produced through the 

hydrogenolysis of thiophene and probably from β-H elimination from intermediate hydrogenated thiophenes [55]. 

Table 2 shows the chemical analysis for the three samples analyzed before and after HDS reaction for more than 

seven hours. The sulfur content for the three samples increased after the HDS reaction. This sulfur content increase 

could be attributed to formation of sulfur species during the HDS reaction by the oxide phases that remain in the 

sample. The sample prepared by OMXC method shows more chemical stability compared to the samples prepared 

by other methods. The reaction rate was calculated for the HDS reaction over the three different catalysts. The 

catalyst prepared using OMXC method a shows higher reaction rate than IMPR and MECH. 

Table 2. Chemical Analysis for NiMoS Catalyst before and after HDS of Thiophene Reaction at 350ºC and 

Atmospheric Pressure 

Methods Before Reaction % After Reaction % Reaction rate 

Al Mo Ni S Al Mo Ni S μmol (g min) -1 

IMPR 47.28 24.49 7.41 20.81 41.61 24.36 5.61 28.42 58.16 

OMXC 46.63 18.60 9.68 25.10 42.46 19.31 9.50 28.74 73.80 

MECH 45.34 18.64 11.35 24.67 36.52 19.74 12.45 31.29 26.05 

The structure stability after the HDS reaction for the three samples was analyzed by X-ray and Raman 

spectroscopy. The X-ray patterns (Figure 7) for all the samples show higher structure stability after the HDS 

reaction. The remaining peaks of MoO3 over the MECH sample after sulfurization reaction were converted to the 

sulfide phase. 

Raman spectra for the three samples after HDS reaction are shown in Figure 8. It is shown that all bands for 

Mo=O and Mo–O–Mo vibrations at 995 cm –1 and 830 cm –1 on the IMPR sample are eliminated during the HDS 

reaction. There is also a reduction in band 965 cm –1 for the MECH sample. 

January 2009 The Arabian Journal for Science and Engineering, Volume 34, Number 1A 

HD

Count/arb. units 

500 

400 

300 

200 

100 

0 

0 10 20 30 40 50 60 70 


Figure 7. XRD pattern for Ni 3Mo 7S x/Al 2O 3 catalysts used for HDS reaction at 350ºC, atmospheric pressure and 20ml/min flow of 

hydrogen. 

Ramman Band Intincity 

1000 

800 

600 

400 

200 

0 

2 q 


MECH 

OMXC 

I MPR 

MECH 

OMXC 

I MPR 

500 1000 1500 2000 

Ramman Shift. cm -1 

Figure 8. Laser Raman spectra for Ni 3Mo 7S x/Al 2O 3 catalysts used for HDS at 350ºC, atmospheric pressure and 20ml/min flow of 

hydrogen. 

4. CONCLUSION 

The Ni–Mo–Al2O3 catalysts were prepared by impregnation (IMPR), Mechanical (MECH), and organic matrix 

combustion (OMXC) methods. The differences in the surface area of the catalysts are relatively small and range 

between 119.3, 122.5, and 125.5 m 2 /g for MECH, OMXC and IMPR respectively. XRD examination of IMPR, 

MECH, and OMXC catalysts indicated high dispersion of Ni3Mo7Ox in the OMXC catalyst as compared to the 

MECH and IMPR catalysts. XRD also indicated the disappearance of MoO3 after sulfidization of the catalysts. This 

could be attributed to higher formation of the sulfide phase. The disappearance of MoO3 was also observed in the 

Raman spectra. 

It was found that the OMXC catalyst has superior activity towards HDS of thiophenes, as compared to IMPR and 

MECH catalysts.

64 


In summary, a new method has been developed to prepare HDS catalyst and this catalyst has been compared with 

catalysts prepared by the conventional methods for selective thiophene HDS. This method enables a high dispersion 

of the molybdenum oxide and sulfide, resulting in higher activity and high yield of olefin in thiophene HDS. 

ACKNOWLEDGMENT 

The author would like thank Eng. Saeed Alshihri, Eng. Saud Aldrees, and Mr. Rasheed Al-Rasheed for their help 

in experimental work in the laboratories of King Abdulaziz City for Science and Technology. The author would 

also like to thank the Inorganic Chemistry Laboratory (ICL) at the University of Oxford, England, for their 

assistance in this research. 

REFERENCES 

[1] C. Song, X. Ma, “New Design Approaches to Ultra-Clean Diesel Fuels by Deep Desulfurization and Deep 

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