Zinc-Modified MCM-22 as Potential Solid acid Catalyst for Friedel–Crafts Alkylation Reaction

Sharad V. Lande*, A. Sakthivel, K. V. V. S. B. S. R. Murthy, Unnikrishnan Sreedharan,Jagannath Das and Raksh Vir Jasra

Zinc-Modified MCM-22 as Potential Solid acidCatalyst for Friedel–Crafts Alkylation Reaction

Abstract: In this paper, we report loading of ZnCl2 onmicroporous medium pore high surface area zeolite,which was achieved by incipient wetness method. Thezinc-modified mobil composite material-22 (Zn-MCM-22)was systematically characterized by powder X-ray diffrac-tion, N2 adsorption-desorption analysis, scanning electronmicroscopy and Fourier transform infrared spectroscopy.The acidity of the materials was studied by temperatureprogrammed desorption of ammonia analysis. The well-characterized Zn-MCM-22 catalyst was investigated for theFriedel–Crafts alkylation of benzene by benzyl chloride inliquid phase medium. A systematic investigation of var-ious operating parameters like effect of different tempera-ture, catalyst loading and reactant molar ratio was carriedout. The Zn-MCM-22 found to be promising, further thecatalytic activity remains stable over several recycles.

Keywords: Friedel–Crafts alkylation, MCM-22, Zn-MCM-22,zeolite, microporous material

*Corresponding author: Sharad V. Lande, Reliance TechnologyGroup, Reliance Industries Ltd., Vadodoara Manufacturing Division,Vadodara, Gujarat, 391346, India,E-mail: [email protected]. Sakthivel Department of Chemistry, Delhi University (NorthCampus), Delhi 110 007, India, E-mail: [email protected]. V. V. S. B. S. R. Murthy: E-mail: [email protected],Unnikrishnan Sreedharan: E-mail: [email protected],Jagannath Das: E-mail: [email protected], Raksh Vir Jasra:E-mail: [email protected], Reliance Technology Group, RelianceIndustries Ltd., Vadodoara Manufacturing Division, Vadodara, Gujarat,391346, India

1 Introduction

Friedel–Crafts reaction is ubiquitous in fine chemicals,intermediates and petrochemical industries. Stronglyacidic catalysts are normally employed in the Friedel–

Crafts reaction. The liquid phase benzylation of benzeneand other aromatic compounds by benzyl chloride (BC),hereafter indicated as BC, or benzyl alcohol is importantfor the production of diphenylmethane, denoted by DPM,and substituted diphenylmethanes which are industriallyimportant compounds used as pharmaceutical intermedi-ates and fine chemicals [1–4]. Such reactions are carriedout industrially, using conventional strong homogeneousacid catalysts, such as AlCl3, FeCl3, BF3, ZnCl2 and H2SO4

[1,5]. However, these catalysts pose several problems,such as toxicity, potential hazards in handling, difficultyin separation and recovery of the catalyst, products iso-lation, disposal problems due to large amounts of acidiceffluents, corrosion and their requirement in stoichio-metric amounts. Thus, there has been a lot of interest toreplace these homogeneous catalysts by heterogeneoussolid acid catalysts, which can easily be separated fromthe reactant mixture and reused. They also have highactivity for Friedel-Crafts-type reactions. Indeed, severalsolid acid catalysts have already been proposed which areefficient catalysts such as: Fe-modified ZSM-5 and H-βzeolites; Fe2O3 or FeCl3 deposited on micro-, meso- andmacro-porous [6]; Fe-containing mesoporous molecularsieves materials [7,8,]; Fe-, Zn-, Ga- and In-modifiedZSM-5-type zeolite catalysts [9]; Ga and Mg-oxides andchlorides derived from Ga-Mg-hydrotalicite [10]; Ga-SBA-15 [11]; Ga-HMS [12]; InCl3, GaCl3, FeCl3 and ZnCl2 sup-ported on clays and Si-MCM-41 [13]; supported thalliumoxide catalysts [14]; Sb supporting K10 [15] solid superacid and silica-supported polytrifluoro-methanesulfosiloxane [16]; Si-MCM-41-supported Ga2O3 and In2O3 [17];H2SO4, HNO3 and HClO4/metakaolinite[18]; alkali metalsalts and ammonium salts of keggin-type heteropolyacids[19]; ion-exchanged clays [20]; clayzic [21]; solid superacids based on sulfated ZrO2 [22,23]; HY [24]; H-ZSM-5[25] and FeCl3, MnCl2, CoCl2, NiCl2, CuCl2, ZnCl2 supportedon acidic alumina [26] for the benzylation of benzeneand other aromatic compounds. mobil compositematerial (MCM)-22 has been widely used in many

doi 10.1515/ijcre-2012-0080 International Journal of Chemical Reactor Engineering 2013; 11(1): 407–415

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catalytic transformation processes of hydrocarbons suchas isomerization, alkylation, aromatization and cracking[27–29]. In this work, we report the benzylation ofbenzene using BC as alkylating agent over zinc chloridesupported on MCM-22. We have also studied the effectof various process parameters like catalyst loading,temperature, reactant mole ratio and reusability of thecatalyst.

2 Experimental

2.1 Chemicals and catalyst

All chemicals and solvents used in this study were com-mercially available and used without further purification.Benzene, BC and zinc chloride all of AR grade wereobtained from M/s S.D. Fine Chemicals Pvt. Ltd.,Mumbai, India. The following chemicals: colloidal silica(SiO2, 40 wt%; Aldrich), hexamethylenimine (HMI;Aldrich), sodium aluminate, (50–56 wt% Al2O3 and40–45 wt% Na2O; Riedel-deHaën; 9H2O) and sodiumhydroxide (NaOH; Labort Fine Chemical Pvt. Ltd.) areused without purification for the synthesis of the MCM-22 zeolites. MCM-22 was synthesized as per the proceduredescribed in the literature [30], with the molar gel com-position of 1SiO2:0.3NaOH:0.033Al2O3:0.5HMI:40H2O. Theknown amount of HMI was added to an aqueous solutionof NaAlO2 and NaOH. The desired amount of colloidalsilica was added to the above mixture, with continuousstirring. The final gel was transferred in to Teflon linedautoclave and allowed to crystallize for 7–14 days at150°C, with 300 rpm stirring speed. After the crystalliza-tion, the powder product was recovered by filtration,washed, dried and then calcined at 550°C for 6 h. Theproton form MCM-22 was prepared by repeated ion-exchange with 1M ammonium nitrate solution with theprocedure described elsewhere [31]. The SiO2/Al2O3 ratioof 30 was maintained for the parent MCM-22 used for thecurrent studies.

2.2 Preparation of 20% w/w ZnCl2/MCM-22catalyst

Zinc loading was carried out [(5–20 wt%) w/w ZnCl2/HMCM-22] by incipient wetness technique. A knownquantity (0.5–2 g) of dry zinc chloride was weighed accu-rately. This was dissolved in 50 ml of methanol. Thesolution was added in small aliquots of 1 ml each time

to the 10 gm of MCM-22 with constant stirring with a glassrod or kneading it properly. The solution was added attime intervals of 2 min. MCM-22 which was in powderform transformed into a paste, on complete addition ofthe ZnCl2 solution. The paste on further kneading for10 min resulted in a free flowing powder. The preformedcatalyst was dried at 120°C for removal of water and otheroccluded volatiles, and subsequently calcined at 550°Cfor 4 h. The zinc-modified MCM-22 using 5, 10 and 20%ZnCl2 are represented as 5Zn-MCM-22, 10Zn-MCM-22 and20Zn-MCM-22, respectively.

2.3 Catalyst characterization

Powder X-ray diffractograms were recorded by an XRD-6000 diffractometer (Brucker, D8 Advance) with Cu Kαradiation (α = 1.5418 Å). Fourier transform infrared(FT-IR) spectra of the various samples were recorded ona Nicolet 6700 (Thermo Scientific) spectrophotometerwith a 4 cm–1 resolution and 128 scans in the mid IR(400–4000 cm–1) region using KBr pellet technique.Crystal size and morphology of zeolites were determinedby a SEM microscope (Delong LVEM5, 5.0 KV). Nitrogenadsorption measurements were carried out on aMicrometrics ASAP 2000 apparatus. The BET surfacearea, pore volume (BJH method) and the external surfacearea (t-plot method) were used to derive textural proper-ties of various samples. The acidic behavior of the proto-nated catalyst was studied by temperature programmeddesorption of ammonia (NH3-TPD) with Chemisorb 2750(Micrometrics).

2.4 Experimental procedure and analysisof catalytic tests

The liquid phase benzylation of benzene with BC was car-ried out in a 50ml two necked flask attached to a condenserand a septum. The temperature of the reaction vessel wasmaintained using an oil bath. In a typical run, benzene andBC were added in the required molar ratio to the activatedcatalyst. The catalysts were activated at 200°C in air for 2 hwith a flow rate of 50 ml/min and cooled to room tempera-ture prior to their use in the reaction. The reaction mixturewas magnetically stirred and heated to the required tem-perature under atmospheric pressure. In all the cases, themajor product formed was mainly mono-benzylated com-pound along with polybenzyl and HCl as byproductsdepending upon the conditions used. A typical reaction

408 S.V. Lande et al.: Zinc-Modified MCM-22


mixture consisted of 0.5 mol of benzene and 0.025 mol ofBC (benzene to BCmole ratio 1:20) with a catalyst loading of0.025 g/cm3 of reactant volume at 80°C. The reaction mix-ture was allowed to reach the desired temperature, theinitial/zero time samples was withdrawn and catalyst wasadded thereafter. Samples were withdrawn at regular inter-vals of time and analyzed periodically on a gas chromato-graph (HP-6890) equipped with a FID detector and acapillary column. Since benzene was in excess, conversionwas calculated based on the benzylating reagent, i.e. BC.

The reaction scheme is as shown below:

3 Results and discussion

3.1 Catalyst characterization

The catalysts were systematically characterized by var-ious spectroscopic and analytical techniques. Figure 1represent the powder X-ray diffraction pattern of parentMCM-22 and 20Zn-MCM-22 which are typical characteris-tic of microporous MCM-22 diffractograms and are well inagreement with literature [30]. The crystallinity of thematerials remains intact even at loading of 20% ZnCl2on it. Furthermore, there is no additional peak appearing

even at high loading of ZnCl2, clearly indicating theabsence of any bulk ZnO phase formation. It also clearlysuggests uniform distribution of Zn within the MCM-22matrix. The SEM image of MCM-22 (Figure 2) showed thatthe material has uniform spherical particles formed bythe tight assembly of MCM-22 materials. The FT-IR spec-trum of MCM-22 (not shown here) showed the vibrationfrequency around 1240, 1065, 837, 607 and 555 cm–1

which are characteristics of zeolite framework vibrations.In particular, the appearance of vibrational band at607 cm–1 and a weak band around 406 cm–1 typical ofdouble six-membered and 12-membered ring vibrations,which are secondary building units of MCM-22 [32].

The textural properties of MCM-22 and the Zn-mod-ified MCM-22 are summarized in Table 1. The BET surfacearea of 531 m2 g–1 and pore volume of 0.52 cm3 g–1

obtained for MCM-22 drastically decreased with increasein Zn loading. Furthermore, the micropore volume ofMCM-22 was found to be 0.194 cm3 g–1, which is inagreement with literature value of characteristics MCM-22 [33]. The micropore volume decreased to 0.12 cm3 g–1

with 5% loading of ZnCl2. However, upon further loadingof ZnCl2 not much change in micropore volume wasobserved, indicating that the loading might be occurringat external pockets of MCM-22 framework. The above factcan be corroborated from the observed decrease in exter-nal surface area with increase in loading of zinc.

The acidity measurement of MCM-22 and Zn-modifiedMCM-22 (see Figure 3) clearly indicate the presence of bothLewis and Brönsted acid sites similar to reported literature[33]. The introduction of Zn into the MCM-22 channelsresults in initial decrease in acidity (while 5% ZnCl2loading). This might be due to possible substitution of

Reaction Scheme

+

CH2Cl

CH2 CH2

CH2

Zn/MCM-22+

20 Zn-MCM-22

MCM-22

Figure 1 Powder XRD pattern of MCM-22 of parent and 20Zn-MCM-22.

S.V. Lande et al.: Zinc-Modified MCM-22 409


Table 1 Textural properties of MCM-22 and Zn-modified MCM-22.

Sample name Surface properties Acidity(mmol/g)

Total Micropore ExternalSurface area(m2/g)BET Surface

area (m2/g)Pore volume(cm3/g–1)

Surface area(m2/g)

Pore volume(cm3/g–1)

H-MCM-22 531 0.52 433 0.194 98 1.51735Zn-MCM-22 306 0.57 211.5 0.12 95 1.168810Zn-MCM-22 303 0.49 216 0.11 87 1.592220Zn-MCM-22 301 0.36 234 0.10 67 2.5031

Figure 3 Ammonia-TPD profile of MCM-22 and 20Zn-MCM-22.

100 µm

Figure 2 SEM image of MCM-22.



Zn2+ cations on proton of bridging hydroxyl (SiOHAlBrönsted acidotic proton) groups which is similar to earlierobservation on Zn-modified zeolite-beta [34]. However,further loading of ZnCl2 (10–20%; see Table 1) results inan increase in total acidity, which is probably due to Lewisacid center arising from Zn moiety on MCM-22.

3.2 Effect of different zinc chloride loadingon MCM-22

The Zn-modified MCM-22 catalysts prepared with differentloading of zinc chloride (5, 10and 20%ZnCl2)were evaluatedfor liquidphasealkylationof benzenewithBCand the resultsare shown in Table 2. It is observed that in case of 5Zn-MCM-22 and 10Zn-MCM-22 catalysts, the initial conversion waslower and reaction did not complete till an hour of duration(Figure 4). However, the higher Zn-loaded catalysts, i.e.20Zn-MCM-22, the reaction proceeded faster and yieldedcomplete BC conversion within 1 h, which might be due toincrease in total acidity of the catalysts as shown in Table 2.The selectivity to mono-alkyl benzene remained in the rangeof 93–97% in all the cases. The observed higher selectivity ofmonobenzylated can be explained based on the size andshape of the sinusoidal channel available on MCM-22(28,29]. The narrow apertures of the sinusoidal channels(4.1 · 5.1 Å), along with small cages (6.4 · 6.9 Å) and at thenarrow channel intersections (5.6 Å) favored less bulkymonobenzylated product. As expected, the use of 20Zn-MCM-22 catalysts favors formation of trace amount of diben-zylation product. In contrast, the catalyst without Zn loading(parent MCM-22) shows only 11.8% conversion after 1 h of

reaction time under identical reaction conditions. Thisclearly demonstrates that Zn acts as catalytic center. The20Zn-MCM-22 seen as the better catalyst among all the sam-ples prepared, was used for further studies like effect ofcatalyst loading, reactant mole ratio, temperature etc. Theactual Zn content in 20Zn-MCM-22 catalyst is 8.75% which isdetermined by ICP analysis.

3.3 Effect of catalyst loading

In the absence of mass transfer resistance, the rate ofreaction is directly proportional to catalyst loading basedon the entire volume of the liquid phase. The catalystloading was varied over a range of 0.01–0.25 g/cm3 onthe basis of the total volume of the reaction mixture.Figure 5 shows the effect of catalyst loading on the con-version of BC. The corresponding impact on selectivity isshown in Table 3. It indicates that as the catalyst loading

Table 2 Effect of zinc chloride loading on mono and dibenzylationselectivity.

Catalyst Time

(min)

Conversion

(%)

Monobenzylation

(%)

Dibenzylation

(%)

H-MCM-22 60 11.8 98.8 1.2

5Zn-MCM-22 60 36.76 97.5 2.5

10Zn-MCM-22 60 59.87 96.8 3.2

20Zn-MCM-22 60 96.89 93.45 6.5

Note: Reaction Condition: benzene 0.5 mol, BC 0.025 mol andtemperature 80°C.

0102030405060708090

100

0 10 20 30 40 50 60

Con

vers

ion,

%

Time ( min.)MCM-22 5 Zn-MCM-22 10-Zn-MCM-22 20 Zn-MCM-22

Figure 4 Effect of zinc chloride loading on conversion.



is increased, the proportional increase in the number ofactive sites results in increase of BC conversion. However,when the catalyst loading is 0.03 (highest catalyst load-ing), the rate of mass transfer is excessively high andtherefore there is no further improvement in reactionrate. Therefore, all further experiments were carried outwith 0.025 g/cm3 of catalyst loading.

3.4 Effect of benzene/BC ratio

The effect of benzene to BC ratio was studied at 5:1,10:1 and 20:1 by keeping the catalyst loading constant.It appears that the stoichiometric ratio between ben-zene and BC has a strong influence on the selectivity todiphenyl methane. With low Benzene to BC (5:1) ratio,the overall concentration of BC was relatively high;hence the selectivity towards dibenzylation improvedconsiderably. The conversion of BC was found to

increase with increase in concentration of BC asshown in Figure 6. The same trend was observed formono benzylated product selectivity as clearly seen inTable 4. Therefore, all reactions were studied by usingbenzene to BC mole ratio 20.

3.5 Effect of temperature

The effect of temperature on the rate of reaction wasstudied by conducting the reaction at 50, 60, 70, 800C,under otherwise similar condition as shown in Figure 7.The conversion of BC linearly increased with increasingtemperature and reached maximum conversion in 1 h at800C. This is likely due to intra-particle diffusion limita-tion. The corresponding selectivities are mentioned inTable 5. It is clearly seen that the monobenzlated productselectivity decreases with increase in reaction tempera-ture whereas the corresponding dibenzylated productselectivity increases.

Table 3 Effect of catalyst loading on mono and dibenzylationselectivity.

Catalystloading(g/cm3)

Time(min)

Conversion(%)

Monobenzylation(%)

Dibenzylation(%)

0.01 60 33.26 97.89 2.110.015 60 73.87 95.73 4.270.025 60 96.89 93.45 6.50.03 60 97.98 92.68 7.32

Note: Reaction Condition: Benzene 0.5 mol, BC 0.025 mol andTemperature 80°C

0102030405060708090

100

0 10 20 30 40 50 60

Con

vers

ion,

%

Time ( min.)0.01 g/cm3 0.015 g/cm3 0.025 g/cm3 0.03 g/cm3

Figure 5 Effect of catalyst loading on conversion.

Table 4 Effect of mole ratio on mono and dibenzylation selectivity.

Benzene:BC

Time(min)

Conversion(%)

Monobenzylation(%)

Dibenzylation(%)

5:1 60 97.88 74.16 25.8410:1 60 97.12 86.33 13.6720:1 60 96.89 93.45 6.5

Note: Reaction conditions: Catalyst loading 0.025 g/cm3 and tem-perature 80°C.



3.6 Reusability of catalyst

Reusability of catalyst was verified by conducting threeruns. After each run, the catalyst was filtered, washedwith methanol and toluene, dried at 120°C overnight.There was some attrition of catalyst particle during agita-tion. In a typical batch reaction, there are inevitable lossesof particles during filtration due to attrition. Although thecatalyst was washed after filtration to remove all adsorbedreactants and products, there was still a possibility ofretention of small amounts of adsorbed reactant and pro-duct species which might cause the blockage of active sitesof the catalyst. These are the apparent factors for the loss inactivity. These have been taken into account by adding

fresh catalyst into the reaction mixture to maintain thesame catalyst loading during reusability test. The catalystcan be efficiently used for three cycles without loss of

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Con

vers

ion,

%

Time (min.)

50 C 60 C 70 C 80 C

Figure 7 Effect of temperature on conversion.

Table 5 Effect of temperature on mono and dibenzylation selectivity.

Temperature(°C)

Time(min)

Conversion(%)

Monobenzylation(%)

Dibenzylation(%)

50 60 45.65 98.45 1.5560 60 63.77 96.88 3.2270 60 83.44 95.75 4.2580 60 96.89 93.45 6.5

Note: Reaction conditions: Benzene 0.5 mol, BC, 0.025 mol andcatalyst loading 0.025 g/cm3.

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Con

vers

ion,

%

Time ( min.)

B/BC 5 B/BC 10 B/BC 20

Figure 6 Effect mole ratio on conversion.



much catalytic activity. The conversions and selectivitiesfor the catalyst reuse runs are shown in Table 6.

4 Conclusion

A series of Zn-modified MCM-22 catalysts were pre-pared and systematically characterized. The acidity

of the materials increases with increase in ZnCl2loading, however, surface area and pore volumedecreased due to effective loading of ZnCl2 on thechannels of MCM-22. Friedel–Crafts alkylation of ben-zene with BC was studied systematically using 20%zinc chloride supported on MCM-22 as solid acid cata-lyst. The effects of various parameters (catalyst load-ing, time, benzene: BC ratio and temperature) werestudied on the rate of reaction under otherwise similarconditions. The catalyst is found to be promising underoptimum reaction conditions (80°C, 1 h, benzene:BC of20 and catalyst loading of 0.025 g/cm3). It is observedthat the catalyst has excellent stability and the reactionis highly selective towards diphenyl methane (mono-alkylated product). The catalyst reusability was estab-lished three times without affecting the activity andselectivity.

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Run Time(min)

Conversion(%)

Monobenzylation(%)

Dibenzylation(%)

Fresh 60 96.89 93.45 6.5First 60 96.45 93.68 6.3Second 60 96.22 93.75 6.25Third 60 95.88 93.88 6.12

Note: Reaction conditions: benzene 0.5 mol, BC, 0.025 mol,temperature 80°C and catalyst loading 0.025 g/cm3.



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Zinc-Modified MCM-22 as Potential Solid acid Catalyst for Friedel–Crafts Alkylation Reaction

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