performance of fluorine-added, sonochemically prepared mos2/al2o3 catalysts in the...

Applied Catalysis B: Environmental 54 (2004) 33–39

Performance of fluorine-added, sonochemically preparedMoS2/Al2O3 catalysts in the hydrodesulfurization

of dibenzothiophene compounds

Heeyeon Kim, Jung Joon Lee, Jae Hyun Koh, Sang Heup Moon∗

School of Chemical Engineering and Institute of Chemical Processes, Seoul National University, San 56-1,Shillim-dong, Kwanak-ku, Seoul 151-744, Republic of Korea

Received 8 March 2004; received in revised form 9 June 2004; accepted 14 June 2004Available online 22 July 2004

Abstract

The performance of MoS2/Al2O3 catalysts, prepared by a sonochemical method and containing different amounts of fluorine, was investi-gated for hydrodesulfurization (HDS), using dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) as model compounds.The activity of sonochemically synthesized MoS2 catalysts was higher than that of impregnated ones due to the improved dispersion of theMo species. The addition of fluorine to the catalyst further increased the activity, reaching a maximum at the optimum fluorine content, due toan increase in acidity at the catalyst surface. The optimum amount of fluorine for maximum HDS activity was higher for the sonochemicallyprepared catalysts than for impregnated ones and, therefore, the activity of the former catalysts can be enhanced by fluorine addition to agreater extent than that of the latter types. The two promoting factors, sonochemical synthesis and fluorine addition, led to an increase inthe hydrogenation (HYD) rates, compared to the direct-desulfurization (DDS) rates, in the HDS of both DBT and 4,6-DMDBT. However,the enhancement in overall activity was greater for the HDS of 4,6-DMDBT, which proceeds mainly via the HYD route, than for the HDSof DBT. The above reaction results, obtained using different catalysts, can be explained based on the surface properties of the catalysts, ascharacterized by X-ray photoelectron spectroscopy (XPS), nitric oxide chemisorption and infrared spectra of adsorbed pyridine.© 2004 Elsevier B.V. All rights reserved.

Keywords: Hydrodesulfurization; Sonochemical synthesis; Fluorine; MoS2; Dibenzothiophene; 4,6-Dimethyldibenzothiophene

1. Introduction

Because of the necessity of complying with the stringentenvironmental restrictions imposed worldwide on the sulfurcontent of diesel fuel, many attempts have been made to im-prove the activity of catalysts for deep hydrodesulfurization(HDS). Some examples include the addition of acidic com-pounds to the catalysts[1–3] and improvement in catalystdispersion using novel preparation methods[4–6].

In our previous studies, we reported that the activitiesof NiMo/Al 2O3 [1], CoMo/Al2O3 [2] and NiW/Al2O3 [3]for the HDS of refractory compounds could be enhanced,but the amounts of cracked products could be maintainedat an insignificant level, by modifying the catalyst surface

∗ Corresponding author. Tel.:+82 2 8807409; fax:+82 2 8756697.E-mail address: [email protected] (S.H. Moon).

with fluorine. For example, in the HDS of dibenzothiophene(DBT) using fluorinated NiMo/Al2O3 as a catalyst, HDSactivity was enhanced by up to 10% due to the improveddispersion of catalytic sites and the increased number ofacid sites, as the result of fluorine addition. In the HDSof 4,6-dimethyldibenzothiophene (4,6-DMDBT), the activ-ity was enhanced by 21% because the added fluorine ad-ditionally facilitated the migration of methyl groups, whichappeared to take place on acid sites[7].

Recently, the sonochemical decomposition of volatileorganometallic compounds has been applied to the synthesisof a variety of nanostructured catalysts[4–6]. For example,the activity of sonochemically synthesized MoS2/Al2O3showed an increase of up to 56% in the HDS of DBTand 4,6-DMDBT due to the improved dispersion of MoS2,the levels of which could be maintained up to 25 wt.%.This is in contrast to the case of conventional impregnatedMoS2/Al2O3, which shows an activity approaching a sat-

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34 H. Kim et al. / Applied Catalysis B: Environmental 54 (2004) 33–39

uration level at Mo contents higher than about 15 wt.%[8].

The objective of this study was to investigate the com-bined effects of the above two promoting factors, fluorineaddition and sonochemical synthesis, on the activity ofMoS2/Al2O3 catalysts with respect to deep HDS. For thispurpose, MoS2/Al2O3 catalysts with different Mo loadingswere prepared by a sonochemical method using�-Al2O3,containing different amounts of fluorine, as a support.The catalysts were characterized by X-ray photoelectronspectroscopy (XPS), nitric oxide (NO) chemisorption andinfrared (IR) spectra of pyridine adsorbed to the catalystsurface.

2. Experimental

2.1. Materials

DBT and 4,6-DMDBT were purchased from Acros.Each catalyst was prepared using fluorinated�-Al2O3 asa support, obtained by impregnating�-Al2O3 (CONDEA,214 m2 g−1 surface area and 0.7 cm3 g−1 pore volume) withan aqueous solution containing various amounts of NH4F,followed by drying in air at 383 K for 12 h and calcinationin air at 723 K for 4 h.

MoS2/Al2O3 catalysts containing different amounts ofMo were sonochemically synthesized by a procedure de-scribed in the literature[8,9]. That is, a hexadecane slurrycontaining Mo(CO)6, S8 and �-Al2O3 was irradiated withhigh intensity ultrasound (Sonics and Materials, modelVCX-600, 1 cm diameter Ti horn, 20 kHz, 100 W cm−2)in an atmosphere of argon (Ar) at 333 K for 1.5 h. Theresulting black powder, the sulfided catalyst, was filteredand washed several times withn-hexane in an inert atmo-sphere of a glove box in order to avoid contamination byoxygen. The washed powder was then heated at 473 K ina vacuum to remove unreacted reactants. These catalystsare referred to hereafter as ‘sonochemically synthesized’MoS2/Al2O3.

Another series of MoO3/Al2O3 catalysts was prepared,for purposes of comparison, by impregnating fluorinated�-Al2O3 with an aqueous solution containing differentamounts of (NH4)6Mo7O24·4H2O, followed by the samedrying and calcination processes as described above. Thesecatalysts, after pre-sulfidation for use in the activity tests,are referred to hereafter as ‘impregnated’ MoS2/Al2O3.

Catalysts with two different Mo loadings, 15 and 25 wt.%,were prepared because, based on our previous study[8], thedispersion of the active species was improved and preservedup to a Mo loading of 25 wt.% when the catalysts were pre-pared by the sonochemical method while the activity reacheda saturation level at 10–15 wt.% Mo loading in the case of theimpregnated catalysts. Each sample catalyst was designatedas FXMoY(i or s), with ‘X’ denoting the nominal amount ofadded fluorine in 0.1 wt.% units and ‘Y’ indicating the Mo

content in 1.0 wt.% units. ‘i’ and ‘s’ denote ‘impregnated’and ‘sonochemically synthesized’ catalysts, respectively.

2.2. Activity test

Before the activity tests, all impregnated catalysts in theoxide phase, FXMoY(i), were pre-sulfided in a 12.9% hy-drogen sulfide/hydrogen mixture at 673 K for 2 h. All HDSreactions were performed in a 100 cm3 autoclave reactor at593 K under a 4.0 MPa hydrogen pressure for 2 h. The reac-tor, containing 0.2 g of catalyst, was charged with 0.1 g ofDBT dissolved in 30 cm3 of n-pentadecane for the HDS ofDBT and with 0.05 g of 4,6-DMDBT dissolved in 30 cm3

of n-dodecane for the HDS of 4,6-DMDBT, respectively.The liquid products were collected and analyzed by gaschromatography (GC) on a silicone capillary column (HP1;0.53 mm in diameter and 30 m long) using a flame ioniza-tion detector.

2.3. Surface characterization

XPS spectra were obtained using an ESCALAB 220i-XLinstrument equipped with an aluminum anode (Al K�= 1486.6 eV). The catalyst powder, in the sulfide phase,was covered with isooctane for protection against air ox-idation, pressed into a thin wafer, which was mounted ona double-sided adhesive tape for the XPS measurements.Binding energy (BE) data were obtained with reference tothe BE of the Al 2p line at 74.6 eV.

The amounts of NO chemisorbed to the catalysts in sulfidephase were measured by a dynamic method, as previouslydescribed in the literature[10,11]. The impregnated catalystswere pre-sulfided following the same process as was used forthe activity test, cooled to room temperature, and exposed toa helium flow for 1 h, prior to NO chemisorption. Pulses ofthe adsorption mixture (5 vol.% NO/Ar) were then injectedinto the helium stream. The amount of NO eluted after eachinjection was monitored until three successive pulses gaveoutlet signals with a change in intensity of<1%. In order toremove physically adsorbed NO from the catalyst surface,the catalyst was flushed with helium at 373 K for 1 h andthe NO injection procedure was repeated. The amount ofchemisorbed NO was calculated from the difference in NOuptake between the first and the second adsorption cycles[12,13].

The vacuum cell used in the infrared spectroscopic inves-tigation of the catalyst has been previously described[14].The catalyst sample, in the form of a self-supporting thinwafer, was placed at the center of the cell vertical to the IRbeam and the spectrum was scanned with a Midac infraredspectrometer. After evacuating the cell, containing the cat-alyst wafer, to below 10−5 Torr at 673 K for 2 h, pyridinewas introduced into the cell at 2 Torr and room temperaturefor the IR observation of pyridine adsorbed to the catalyst.For the removal of the physisorbed pyridine from the cata-lyst surface, the cell was evacuated again while being heated

H. Kim et al. / Applied Catalysis B: Environmental 54 (2004) 33–39 35

from room temperature to 423 K and finally an IR spectrumof the catalyst, containing chemisorbed pyridine, was ob-tained.

3. Results

3.1. Fluorine contents

Our XPS observation of FXMo15 catalysts containing dif-ferent amounts of fluorine indicated, although the results arenot shown here, that the binding energy of Mo 3d was unaf-fected by the fluorine content. On the other hand, the bindingenergy of the added fluorine, represented by the F 1s peakshown inFig. 1, changed from 685.9 to 687.5 eV, the lattercorresponding to the energy for AlF3 [11], when the fluorinecontent is equal to 4 wt.% and higher. This indicates that theaddition of excess amounts of fluorine to Al2O3 causes theformation of AlF3, which is known to block alumina poresin the calcination step[11].

We estimated the amounts of fluorine remaining in thecatalysts, after the fluorine-added Al2O3 had been calcinedfor use in catalyst preparation, based on the peak intensityratio of F 1s/Al 2p in the XPS spectra.Fig. 2 indicates thatthe fluorine content of FXMo15(s) increases in parallel withthe amount of added fluorine.

3.2. HDS reactions

3.2.1. The HDS of DBTTable 1shows the results of DBT HDS using FXMo15 and

FXMo25 for both cases of impregnation and sonochemicalpreparation. In the case of the fluorine-free catalysts, the ac-

Fig. 1. XPS spectra of the F 1s peak of FXMo15(s): (a) F00Mo15(s); (b)F20Mo15(s); (c) F40Mo15(s); (d) F60Mo15(s); (e) F80Mo15(s).

Fig. 2. Peak intensity of F 1s of FXMo15(s) catalysts containing differentamounts of fluorine.

tivities of the sonochemically synthesized catalysts are sig-nificantly higher than those for the impregnated ones. Thatis, the conversion obtained using F00Mo15(s) is more than2-fold higher than that obtained using F00Mo15(i) and thatfor F00Mo25(s) is more than three times higher than that forF00Mo25(i). The activity of the sonochemically preparedcatalyst is further increased, reaching a maximum, when flu-orine is added. The optimum amounts of fluorine to give themaximum activity are 4.0 and 3.5 wt.% for FXMo15(s) andFXMo25(s), respectively. In the case of impregnated cata-lysts, the activity is decreased by fluorine addition even insmaller amounts than for the sonochemically prepared cata-lysts, as shown inTable 1for F20Mo15(i) and F20Mo25(i).The activity decrease, which is more significant at larger flu-orine contents, is due to the reduction in surface area, similarto the case of NiMo and CoMo/Al2O3 catalyst[1].

Table 1also shows the product distribution obtained whendifferent catalysts are used. Similar to the case of activity,the amounts of individual products are increased by fluorineaddition showing maximum values at the corresponding op-timum fluorine contents. The relative increase in the amountof product is larger for the hydrogenation (HYD) products,cyclohexylbenzene (CHB) plus dicyclohexyl (DCH), thanfor the direct-desulfurization (DDS) product, biphenyl (BP),and therefore the ratio of the HYD/DDS products, shown inFig. 3, increases with fluorine content. In fact, a similar trendwas observed with the impregnated catalysts, NiMo/Al2O3[1] and CoMo/Al2O3 [2]. It is noteworthy inFig. 3 thatthe increase in the HYD/DDS product ratio by fluorine ad-dition is larger when the Mo loading is higher, i.e., largerfor FXMo25(s) than for FXMo15(s). This result is in con-trast to the case of impregnated catalysts, which show nearlythe same extents of increase in product ratios, for Mo load-


Table 1HDS of DBT on the FXMoY(i or s) catalystsa

Catalyst Conversion (%) (relative values) Amounts of products,×10−5 mol (relative values)

BP CHB DCH

F00Mo15(i) 19.50 (1.00) (1.00) 3.39 (1.00) (1.00) 1.77 (1.00) (1.00) 0.12 (1.00) (1.00)F20Mo15(i) 17.17 (0.88) 2.85 (0.84) 1.81 (1.02) 0.00 (0.00)

F00Mo15(s) 45.88 (1.00) (2.35) 7.73 (1.00) (2.28) 3.82 (1.00) (2.16) 0.90 (1.00) (7.50)F20Mo15(s) 50.89 (1.11) 8.29 (1.07) 4.43 (1.16) 1.09 (1.21)F40Mo15(s) 54.54 (1.19) (2.80) 8.64 (1.12) 4.93 (1.29) 1.23 (1.37)F60Mo15(s) 47.11 (1.03) 7.37 (0.95) 4.37 (1.14) 1.04 (1.16)

F00Mo25(i) 21.48 (1.00) (1.00) 3.52 (1.00) (1.00) 2.15 (1.00) (1.00) 0.16 (1.00) (1.00)F20Mo25(i) 14.50 (0.68) 2.56 (0.72) 1.37 (0.64) 0.00 (0.00)


a Error range of conversions and product amounts is±2%.

ings higher than 10–15 wt.%[8]. The reason for this dis-crepancy between the two types of catalysts is discussed inSection 4.2.

3.2.2. The HDS of 4,6-DMDBTTable 2shows the results of 4,6-DMDBT HDS obtained

using the different catalysts. The enhancement in activitydue to the combined effects of the fluorine addition andsonochemical synthesis is much larger for FXMo25 than forFXMo15. In other words, the conversion for F00Mo25(s) isca. 7-fold higher than that for F00Mo25(i) and the conver-sion for F35Mo25(s) is further increased, becoming 11-foldhigher than that for F00Mo25(i). When the Mo loading is15 wt.%, the conversion for F40Mo15(s) is 6-fold higherthan that for F00Mo15(i) as a result of the combined effects.Similar to the case of DBT HDS, the maximum activitiesare obtained at fluorine contents of 3.5 wt.% for FXMo25(s)and 4.0 wt.% for FXMo15(s).

The activities of the impregnated catalysts, containingeither 4.0 or 3.5 wt.% for the Mo loading of 15 or 25 wt.%,

Fig. 3. Relative amounts of hydrogenated products to directly desulfurizedproducts in DBT HDS: (a) F00Mo15(i); (b) F00Mo15(s); (c) F40Mo15(s);(d) F60Mo15(s); (e) F00Mo25(i); (f) F00Mo25(s); (g) F35Mo25(s); (h)F50Mo25(s).

respectively, are also given inTable 2. The activity ofF40Mo15(i) is higher than that of F00Mo15(i) because thepromotion of the HYD step, which is the major route of4,6-DMDBT HDS, on the acidic sites produced by fluorineaddition compensates for the lowering of Mo dispersion,as reported in our previous study[1]. The activity increaseis smaller for F35Mo25(i) than for F40Mo15(i) becausethe lowering of Mo dispersion by fluorine addition ismore significant for the former catalyst due to higher Moloading.

Fig. 4 indicates that fluorine addition increases the yieldof HYD products, methylcyclohexyltoluene (MCHT) plusdimethyldicyclohexyl (DMDCH), to larger extents than theDDS product, dimethylbiphenyl (DMBP), which follows thesame trend as observed for the DBT HDS (Section 3.2.1). Inthe case of the sonochemically synthesized catalysts, HYDproduction is increased dramatically due to the improvedmetal dispersion[8,9] and the increased surface acidity, asthe result of fluorine addition[1]. Similar to the case of

Fig. 4. Relative amounts of hydrogenated products to directly desulfu-rized products in 4,6-DMDBT HDS: (a) F00Mo15(i); (b) F00Mo15(s);(c) F40Mo15(s); (d) F60Mo15(s); (e) F00Mo25(i); (f) F00Mo25(s); (g)F35Mo25(s); (h) F50Mo25(s).


Table 2HDS of 4,6-DMDBT on the FXMoY(i or s) catalystsa

Catalyst Conversion (%) (relative values) Amounts of products,×10−5 mol (relative values)

DMBP MCHT DMDCH

F00Mo15(i) 9.09 (1.00) (1.00) 0.58 (1.00) (1.00) 0.99 (1.00) (1.00) 0.57 (1.00) (1.00)F40Mo15(i) 11.90 (1.31) 0.62 (1.07) 1.56 (1.58) 0.63 (1.11)


F00Mo25(i) 8.62 (1.00) (1.00) 0.58 (1.00) (1.00) 0.97 (1.00) (1.00) 0.49 (1.00) (1.00)F35Mo25(i) 9.03 (1.05) 0.40 (0.69) 1.21 (1.25) 0.52 (1.06)


a Error range of conversions and product amounts is±2%.

DBT HDS, the increase in the HYD/DDS product ratio asthe results of fluorine addition is larger for FXMo25(s) thanfor FXMo15(s).

3.3. Characterizations

3.3.1. NO chemisorptionFig. 5 shows the amounts of NO, a molecule that is typ-

ically used for probing the edge and corner sites of MoS2structures[12], chemisorbed to a series of FXMoY(s) cata-lysts as well as to fluorine-free impregnated catalysts.

In the case of FXMo15, the amount of NO adsorbed toF00Mo15(s) is in excess of two times larger than that ad-sorbed on F00Mo15(i). The amount remains nearly con-stant and independent of the fluorine content up to 4.0 wt.%,

Fig. 5. Amounts of NO chemisorbed to FXMoY(i or s).

and then decreases with further fluorine addition. The sametrend is observed for FXMo25, although the amount ad-sorbed to F00Mo25(s) is about three times larger than thatto F00Mo25(i).

3.3.2. Pyridine-IRFig. 6 shows infrared spectra of pyridine adsorbed to

FXMo15(s), which provides a measure of the surface acid-ity of the catalysts containing different amounts of fluorine.The peak at 1540 cm−1 represents Brönsted acid sites andthe other peaks, including the 1450 cm−1 peak, are assignedto Lewis acid sites[15]. Similar to the case of impregnatedcatalysts[1], the number of Brönsted acid sites is signifi-cantly increased by fluorine addition, while that of Lewisacid sites remains virtually unchanged.

Fig. 6. IR spectra of FXMo15(s): (a) F00Mo15(s); (b) F20Mo15(s); (c)F40Mo15(s).


4. Discussions

4.1. Enhancement in HDS activity

It was shown inTables 1 and 2that the HDS of DBT and4,6-DMDBT was dramatically promoted due to the com-bined effects of the sonochemical synthesis and fluorine ad-dition. The activity increased, eventually reaching a maxi-mum, as the fluorine content was increased for both impreg-nated (previous study[1]) and sonochemically synthesized(present study) catalysts, but the optimum fluorine contentsrequired to yield the maximum activity were larger for thelatter catalysts than for the former. The discrepancy in theoptimum fluorine contents between the two types of cata-lysts can be explained as follows.

The HDS activity, which is increased by fluorine addi-tion, is eventually decreased when excessive amounts of flu-orine are added because the surface area of the catalysts de-creases, due to the collapse of the thin walls between themicropores of Al2O3 and pore blockage as the result ofAlF3 formation[11]. In the case of the sonochemically syn-thesized catalysts, the maximum activity occurred at fluo-rine contents of 4.0 wt.% for FXMo15(s) and 3.5 wt.% forFXMo25(s), even though the Al2O3 surface area was de-creased at fluorine contents higher than 1.0 wt.%. The reasonfor the continued increase in activity beyond 1.0 wt.% addedfluorine is because the positive effect of acid-site generationby fluorine addition, which is magnified on the highly dis-persed, sonochemically synthesized catalysts, compensatesfor the negative effect of the reduced Mo dispersion due tothe loss in alumina surface at high fluorine contents. Theimproved dispersion of Mo on the sonochemically synthe-sized catalysts was confirmed by NO chemisorption (Fig. 5)and the generation of acid sites by fluorine addition by thepyridine-IR observations (Fig. 6). In the case of impreg-nated catalysts, the dispersion of Mo is relatively low and,accordingly, the positive effect of fluorine addition is dom-inated by the negative effect of surface area reduction[1]for fluorine contents in excess of 1.0 wt.%. The activityof the sonochemically synthesized catalysts eventually de-creases for added fluorine contents above 3.5–4.0 wt.%, asthe surface area loss becomes significant due to pore block-age.

The optimum fluorine content is smaller for FXMo25(s),3.5 wt.%, than for FXMo15(s), 4.0 wt.%, because thedispersion of Mo is lower for FXMo25(s) than forFXMo15(s).

4.2. Enhancement in hydrogenation activity

In both cases of DBT and 4,6-DMDBT HDS, the HYDproducts are increased to greater extents than the DDS prod-ucts, which is also believed to be the result of the combinedeffects of sonochemical synthesis and fluorine addition. Asthe dispersion of Mo is improved by sonochemical synthesis[8,9], the number of corner sites, responsible for the HYD

Fig. 7. Intrinsic activity of MoS2/Al2O3 in the HDS of DBT and4,6-DMDBT.

route, is increased to a greater extent than that of edge sites,which are responsible for the DDS[16–18]. HYD activityis further enhanced by added fluorine, which generates in-creased numbers of acid sites, which is known to promotethe HYD route[19,20].

The enhancement in HYD activity as the result of theabove two factors should be greater for FXMo25(s) thanfor FXMo15(s) because the former catalyst contains a largeramount of dispersed MoS2 crystallites than the latter. TheHDS activity is enhanced to a greater extent in the case of4,6-DMDBT than DBT because the HDS of 4,6-DMDBT,which is subject to steric hindrance by methyl groups at-tached to the ring structure, proceeds largely via the HYDroute. For the same reasons, the decrease in HDS activitydue to excessive amounts of fluorine is larger for FXMo25(s)than for FXMo15(s) and in the HDS of 4,6-DMDBT thanDBT.

Fig. 7shows that the intrinsic activities of the fluorine-freecatalysts in DBT HDS are nearly the same irrespective ofMo loading as well as the method used to prepare the cata-lysts. The activity of sonochemically synthesized catalyst isincreased slightly with fluorine content due to the enhancedHYD activity, as explained above concerning product dis-tribution. In the HDS of 4,6-DMDBT, the intrinsic activi-ties of fluorine-free catalysts are not affected by Mo load-ing but are higher for the sonochemically synthesized cat-alysts than for the impregnated ones, which is in contrastto the case of DBT HDS. The reason for this is becausethe HDS of 4,6-DMDBT proceeds mainly via the HYDroute, due to steric hindrance by methyl groups, which ispromoted to a greater extent on the highly dispersed, sono-chemically prepared catalysts than on the impregnated cat-alysts with relatively low Mo dispersions[8,9]. The activityof the former catalysts is increased by fluorine addition to agreater extent in 4,6-DMDBT HDS than in DBT HDS be-cause the enhancement in HYD rate is larger in the formerreaction.


5. Conclusions

MoS2/Al2O3 catalysts containing different amounts offluorine were prepared by sonochemical method and theirperformance in the HDS of DBT and 4,6-DMDBT was ex-plained based on the characterization of the catalyst by XPS,NO chemisorption and pyridine IR.

The HDS activity of sonochemically synthesized MoS2catalysts is superior to that of impregnated ones due to theimproved dispersion of Mo species. The activity is increasedfurther by fluorine addition, due to an increase in the acidityof the surface of the catalyst, and shows a maximum at theoptimum fluorine content, which is higher than that in thecase of impregnated catalysts. The activity is decreased bythe addition of excessive amounts of fluorine because thecatalyst loses some of its initial surface area. The extent ofactivity enhancement due to the two promoting factors aregreater for catalysts with higher Mo loading and in the HDSof 4,6-DMDBT than that in DBT HDS.

In the HDS of both DBT and 4,6-DMDBT, the HYDproducts are increased to a greater extent than the DDSproducts by the two promoting factors. The reason for this isbecause the amounts of HYD sites are increased to a greaterextent than those of the DDS sites due to the improveddispersion of Mo species as the result of the sonochemicalsynthesis and, moreover, an increase in surface acidity byfluorine addition facilitates the HYD route.

In DBT HDS, the intrinsic activity of the catalyst isvirtually unaffected by Mo loading and the preparationmethod but is slightly increased by fluorine addition due tothe increased HYD activity of the catalyst. In the HDS of4,6-DMDBT, however, the intrinsic activity is significantlyincreased when the sonochemical synthesis is used and withfluorine addition because the reaction proceeds largely viathe HYD route, which is significantly facilitated by the twopromoting factors.

Acknowledgements

This work was supported by R&D Management Center forEnergy and Resources, Brain Korea 21 project, and NationalResearch Laboratory program.

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performance of fluorine-added, sonochemically prepared mos2/al2o3 catalysts in the...

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