Applied Clay Science 48 (2010) 431–437

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Applied Clay Science

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Epoxidation of olefins on photoirradiated TiO2-pillared clays

Siham Ouidri a, Chantal Guillard b, Valérie Caps b, Hussein Khalaf a,⁎a Laboratory of Chemical Engineering (LGC), University Saad Dahlab of Blida, PO Box 270-09000 Blida, Algeriab IRCELYON, CNRS UMR 5256/Université Lyon 1, 2 av. Albert Einstein 69626, Villeurbanne Cedex, France

⁎ Corresponding author. Tel./fax: +213 25433631.E-mail address: khalafh@hotmail.com (H. Khalaf).

0169-1317/$ – see front matter © 2010 Elsevier B.V. Aldoi:10.1016/j.clay.2010.01.018

a b s t r a c t

a r t i c l e i n f o

Article history:Received 19 September 2009Received in revised form 27 January 2010Accepted 29 January 2010Available online 8 February 2010

Keywords:EpoxidationOlefinsPhotocatalysisPillared clay

The epoxidation of cyclohexene by molecular oxygen was investigated by photoirradiated TiO2-pillaredmontmorillonite (Ti-montmorillonite). This reaction selectively produced cyclohexene epoxide as majorproduct. The effects of reaction parameters such as reaction time, pillaring process of the clay mineral, Ti-montmorillonite concentration and solvent nature in the epoxidation of cyclohexene are discussed. Ti-montmorillonite showed higher selectivity for cyclohexene epoxide than TiO2 (Degussa P25), due to thedifferent specific surface area and hydrophobic nature of the pillared montmorillonite. The maximum yieldsof cyclohexene epoxide using Ti-montmorillonite and TiO2 P25 were 45 and 30%, and the maximumselectivities were 45 and 30%, after 8 h reaction time at optimal experimental conditions. Other olefins werealso tested, and the activity decreased in the order cycloocteneNcyclohexeneN1-hexeneN1-octene.

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1. Introduction

Catalytic epoxidation of alkenes is both an important industrialreaction and useful synthetic method for the production of a widevariety of fine chemicals, because they are derived directly fromalkenes, a primary petrochemical source (Ulmann's encyclopedia,1998). Epoxides are versatile intermediates in organic synthesisbecause they can easily undergo ring opening to form mono- or bi-functional compounds (Rao, 1991; Schwesinger and Bauer, 1995;Neumann and Dahan, 1997; Hill, 1999; Jones, 1999; Ishii et al., 2001;Sheldon and van Vliet, 2001). Generally, epoxides can be formed fromcorresponding alkenes by oxidation on both the laboratory andindustrial scales (Grigoropoulou et al., 2003). Many efforts have beenmade to develop methods of epoxidation (Tabushi and Koga, 1979;Mansuy et al., 1983; Yamada et al., 1992; Mukaiyama and Yamada,1995; Xi et al., 2001; Wang et al., 2005; Petrovski et al., 2005; Zhanget al., 2006; Farahani et al., 2006; Jhung et al., 2006; Abrantes et al.,2009; Miao et al., 2009a; Quionero et al., 2009; Roldan et al., 2009;Serrano et al., 2009; Wang et al., 2009). Industrially, with theexception of ethylene, which is directly oxidized by oxygen, mostalkenes are epoxidized by peroxides or peracids in organic solvents (Liand Chan, 1997). For example, MoO3/SiO2 is used as a catalyst in theliquid phase epoxidation of propylene with cumene hydroperoxide(CHP) (Miao et al., 2009b). Another important industrial processcommercialized in March 2003 by Sumitomo involves a titanium-based catalyst.

Cyclohexene epoxide is a valuable organic intermediate, used inthe synthesis of products such as chiral pharmaceuticals, pesticides,epoxy paints, rubber promoters, dyestuffs, plant-protection agentsand stabilizers for chlorinated hydrocarbons (Bhattacharjee andAnderson, 2006; Sreethawong et al., 2006). Epoxidation of cyclohex-ene has been widely investigated using several metal catalysts underboth homogeneous and heterogeneous conditions (Ravikumar et al.,1998; Raja et al., 1999; Fraile et al., 2003; Kotova et al., 2003; Dinget al., 2004; Qi et al., 2005; Rahiman et al., 2006; Castamana et al.,2009, Dinda et al., 2009; Jiang et al., 2009; Lee et al., 2009; Lin et al.,2009; Stamatisa et al., 2009; Tangestaninejad et al., 2009). Prasad et al.(2006) showed that the oxidation of cyclohexene over titaniummesoporous materials yielded cyclohexene epoxide as major product(a conversion of 70.2% and a selectivity of 95.1%). Heterogeneousphotocatalysis employing semiconductive photocatalysts, such asTiO2, can offer an alternative catalytic oxidation technology, becausethe reaction is promoted under ambient temperature and pressure.Ohno et al. (1998a,b, 2001), reported that olefins, such as 1-decene, 1-hexene and 2-hexene, are converted to the corresponding epoxides byUV-irradiated TiO2 particles with yields of 68, 79 and 83%. Photo-oxygenation of olefins, especially aromatic olefins, using TiO2 particleswas previously reported by Kanno et al. (1980), Fox and Chen (1981),and Fox (1983). However, in most of their results, the main productswere not epoxides, but carbonyl compounds. Although the yields ofepoxides in all these studies were low, their generation on photo-catalysts using molecular oxygen as the oxidant incited most researchon this field. The photogenerated holes on TiO2 possess high energy,leading to a complete oxidation of most organic compounds. In orderto use it as a selective oxidation catalyst for fine chemical production,it is necessary to control its high oxidation power (Shimizu et al.,2002). For improving the selectivity in catalyzed oxidation, the

Fig. 1. Scheme of photoreactor.

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addition of promoters to the catalyst or formation of mixed oxides ledto some improvement, but such attempts were not successful for thephotocatalysis by TiO2. According to Mu et al. (1989) and Pichat(1994), this is due to the impurities and defects produced by suchmodificationswhich can drastically decrease the activity by increasingthe recombination rate of the photoproduced charges. On the otherhand, there are some solvent effects on the epoxidation of olefins(Bahramian et al., 2006; Fan et al., 2006; Tangestaninejad et al., 2006).For example, Fan et al. (2006) showed that acetonitrile should be thesolvent of choice in the epoxidation of cyclohexene considering bothconversion and selectivity (21.2 and 90.8% respectively). A similarresult was reported by Ding et al. (2004), (80% conversion ofcyclohexene and 97% selectivity for cyclohexene epoxide). It istherefore expected that the effectiveness of TiO2 photocatalysts forthe partial oxidation reaction can be improved by controlling reactionenvironments.

TiO2-pillared montmorillonite provides large surface areas andpore volumes (Yamanaka et al., 1987; Malla et al., 1989; Yoneyamaet al., 1989; Kitayama et al., 1998; Ding et al., 1999; Ooka et al.,1999) which are beneficial for organic compounds to reach andleave the active sites on the surface. The size of the TiO2 pillarsincorporated between the silicate layers is of nanometer dimension.TiO2-pillared montmorillonite as effective for the photocatalyticdegradation of organic substrates and exhibited shape selectivitybecause of its pore structure (Yoneyama et al., 1989; Ding et al.,1999; Ooka et al., 1999). It is also expected that the adsorptionbehavior of photocatalysts can be changed by intercalating TiO2

particles in clay mineral and hence different properties can beobtained for the photocatalytic reaction, depending on the surfaceproperties of the clay mineral.

The aim of the present study was to use TiO2-pillared montmo-rillonite for the photo-epoxidation of cyclohexene.

2. Experimental

2.1. Preparation of oxidation catalysts

The pillared montmorillonite was prepared using bentonite fromdeposits of Maghnia in Western Algeria. Its chemical composition(mass%) was: SiO2, 69.4; Al2O3, 14.7; Fe2O3, 1.2; MgO, 1.1; K2O, 0.8;Na2O, 0.5; CaO, 0.3; TiO2, 0.2; and As, 0.05, (Khalaf et al., 1997).According to a previously reported procedure (Khalaf et al., 1997), thepurified bentonite was dispersed in 1 M NaCl, separated from thesolution and washed with water until a constant conductivity wasobtained. The resulting dispersion was placed in a graduated cylinderfor allowing particles N2 μm in size to settle down. The dispersion atthe depth of 10 cm containing only particles of size b2 μm wascollected with a “Robinson–Kohn” pipette. This operation wasrepeated several times until the suspension became almost transpar-ent at the depth of 10 cm. Particles of a size b2 μm were recovered bycentrifugation, washed with water and dialyzed to eliminate chlorideions and dried at 40 °C for 72 h.

TheNa-montmorillonitewas used for the pillaring process followinga procedure previously reported (Yoneyama et al., 1989; Pichat et al.,2005). Titanium tetraisopropoxide in solution was added to hydro-chloric acid (1 M) in order to obtain a HCl/Ti molar ratio of 4. Thissolution was stirred at room temperature for 3 h. The intercalation wasperformedbyadding (dropbydrop) the pillaring solution to anaqueousdispersion of the Na-montmorillonite (1mass%) until a Ti/Na-montmo-rillonite ratio of 10 mmol/g was reached. This mixture, with an acidconcentrationof0.3 M,was stirredat 50 °C for 3 h. Theproductwas thencentrifuged, washed with distilled water until chloride free. The solidwas dried in a microwave oven with an average power of 300W for5 min to remove adsorbed water during the purification and calcinatedfor 15 min at 500W. This pillared sample was referred to as Ti-montmorillonite.

TiO2 for comparison was the well characterized Degussa P25, andhas a BET specific surface area of 50±10 m2/g and an average anatasecrystallite size of 30 nm.

2.2. Measurements

X-ray diffraction (XRD) patterns were obtained using a diffrac-tometer type Philips model PW 1840 with Ni-filtered Cu Kα radiation.Tomaximize the (001) reflection intensities, oriented specimenswereprepared by spreading the sample on a glass slide and drying them atroom temperature for 24 h.

Specific surface areas and pore volumes were determined bynitrogen adsorption at −196 °C in a static volumetric apparatus(Micromeritics ASAP 2010 Sorptometer). The pillared montmorillo-nites were previously outgassed at 180 °C for 16 h under a vacuum of6.6×10−9bar. The specific surface areas were calculated using theBET equation from the linear part of the isotherm, usually locatedbetween 0.05 and 0.30 P/P0, whereas the total pore volumes wereevaluated by measuring the amount of nitrogen physiadsorbed at therelative N2 pressure (p/p0) of 0.99. Themesopore size distributionwasobtained by applying the Barret–Joyner and Halenda (BJH) method tothe adsorption branch of the isotherm (Barrett et al., 1951).

The cyclohexene concentrations were determined by UV–Visiblespectrophotometry on Shimadzu spectrophotometer UVPC 2001, atthe maximum wavelength of the cyclohexene absorption (257 nm).

2.3. Photocatalytic experiments

Photocatalytic reactions were carried out in a cylindrical flask(Ø 40 mm)made of Pyrex (Fig. 1). This flask contained 50 mg of Ti-montmorillonite or 15 mg of TiO2 P25 (this quantity was chosentaking into account that the TiO2 content in the Ti-pillared montmo-rillonitewas about 30% (mass) and an olefin compound (20 mL)). Someexperiments were carried out in the presence of acetonitrile, methylcy-clohexane, carbon tetrachloride and chloroform (1 mLof olefin in20mLof solvent). During thephotocatalytic reactions, oxygengaswasbubbledthrough the mixture at a flow rate of 100 mL/min, and the catalystparticles were dispersed in the liquids with a magnetic stirrer. Thephotoreactor was equippedwith a reflux condenser in order to preventthe olefin evaporation. The dispersions were photoirradiated with a125W Hg lamp at room temperature. The light beam was passedthrough an optical glass filter, to cut off wave-lengths shorter than340 nm. The irradiance spectrum of the Hg lamp (similar to thespectrum inside the reactor) is shown in Fig. 2. The radiation energyincident on the dispersion, measured by using a radiometer VLX-3WDigitalmounted above the lamp at the same position as the photoreactor,

Fig. 2. Irradiance spectrum of the Hg lamp.

Fig. 3. X-ray diffraction pattern of (a) Na-montmorillonite (b) Ti-montmorillonite and(c) TiO2 P25.

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was 40 mWcm−2 (corresponds towavelength of 365 nm). The productsgenerated by photocatalytic reactions were analyzed using a ShimadzuGC-2014 gas chromatography (GC) equipped with a flame ionizationdetector (FID) and SUPELCO equity™ 5 column. Standardswere preparedwith epoxides in their corresponding olefins and in acetonitrile solvent tocalibrate the GC/FID and allow identification of different epoxides. Theirquantificationwas obtained using a calibration curve for each product. Inorder to evaluate the photocatalytic properties of the materials, twoparameters, namely the selectivity and the yield to epoxide, werecalculated to describe the experimental results, as follows:

Selectivity = olefinepoxide½ �= convertedolefin½ �f g × 100%

Yield = olefinepoxide½ �= initialolefin½ �f g × 100%:

3. Results and discussion

3.1. Characterization of catalysts

Investigations on the physicochemical characterization of Ti-pillared montmorillonite have been previously reported (Shimizuet al., 2002; Valverde et al., 2002; Pichat et al., 2005; Damardji et al.,2009). XRD patterns of Na-montmorillonite, Ti-montmorillonite andTiO2 P25 are reported in Fig. 3. Basal spacings are reported in Table 1.Ti-montmorillonite showed reflection at 2θ=25° due to the presenceof anatase phase. The basal spacing of Na-montmorillonite wasincreased to around 22 Å. Thus, titanium species were intercalatedinto montmorillonite a more intense and narrow of the pillaredmontmorillonites whichmay be related to amore homogeneous pillardistribution (Ti pillars similar in size) (Bahranowski and Serwicka,1993).

As a consequence of the pillaring process, the specific surface areawas about three times larger than that of the parent Na-montmoril-lonite. The TiO2 particle is mainly located in the interlayer space aspillars, but is also present on the external montmorillonite surfaces.

Table 1Results of different characterization of catalysts.

Basal spacing (Å) Surface area (m2/g) Micropore

Na-montmorillonite 12.600 78.000 29.000Ti-montmorillonite 22.000 254.000 42.000

The profile of the adsorption isotherms was identical for all thesamples and of type IV, which is characteristic of solids that includeboth micropores and mesopores [BDDT classification] (Sing, 1985).The slope of the isotherms at low relative pressures was increased inthe pillared material as a consequence of the pillaring process (Fig. 4).Ti-montmorillonite contained a bimodal pore size distributioncentered at around 38 Å and 63 Å (Fig. 5). The mesopores werecaused by stacking defects of the particles (Hutson et al., 1999).

3.2. Photocatalytic properties

3.2.1. Effect of reaction timeNo measurable amount of oxidation products (b0.3%) was

obtained in the absence of the photo-irradiation or the catalyst(Figs. 6 and 7). The epoxide yield and selectivity increased sharplywith time in the first 8 h and reached amaximumof 45% after 8 h. Thisis attributed to catalytic ring opening of the generated epoxide toother compounds with prolongation reaction time at full cyclohexeneconversion (Jacobsen, 2000; Zhao et al., 2005).

3.2.2. Effect of catalyst typeCyclohexene epoxide was selectively produced by Ti-montmoril-

lonite (Fig. 8). The yield and the selectivity of cyclohexene epoxidewere 5% and 23% at the beginning of the reaction and increased to 40%and 40% respectively after 10 h, when full cyclohexene conversionwas achieved. The increase of the selectivity of cyclohexene epoxidewith increasing yield is mainly as a consequence of the decrease in the

surface area (m2/g) Micropore volume (cm3/g) Pore volume (cm3/g)

0.014 0.1050.015 0.255

Fig. 4. N2 adsorption–desorption isotherms of (a) Na-montmorillonite and (b) Ti-montmorillonite.

Fig. 5. Pore size distribution of Ti-montmorillonite.

Fig. 7. Concentration of cyclohexene epoxide versus time in the absence of thephotocatalyst reaction conditions: cyclohexene 20 mL (10 mol/L), UV irradiation andoxygen flow rate 100mL/min.

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selectivity and yield of other compounds. It may, also be related to apreferred direct catalytic route of cyclohexene epoxidation, to theslowing down of the epoxide decomposition reaction relative to theolefin epoxidation reaction and to a faster diffusion of the epoxideproduct out of the catalyst, thus preventing further oxidation. OnDegussa TiO2 P25, the yield and the selectivity of cyclohexene epoxidewere 5% and 18% at the beginning of the reaction and 27% and 27%after 10 h (Fig. 8). Thus, pillaring increased the catalytic activity ofTiO2 for the photo-epoxidation of cyclohexene (Table 2). Malla andKomarneni (1990) reported an unusual water adsorption behavior ofvarious pillared clays, which should be indicative of the hydrophobicnature of the surface of the pillared clays. Adsorption isotherms ofcyclohexene on Ti-montmorillonite, Na-montmorillonite and TiO2

P25 (Fig. 9) were carried out in order to justify an extensiveadsorption of cyclohexene (Fig. 9). Ti-montmorillonite exhibited a

Fig. 6. Concentration of cyclohexene epoxide versus time in the absence of irradiationreaction conditions: cyclohexene 20 mL (10 mol/L), catalyst 50 mg (Ti-montmorillon-ite) and oxygen flow rate 100mL/min.

higher affinity for cyclohexene than Na-montmorillonite and TiO2 P25indicating the hydrophobic character of Ti-montmorillonite. A similarresult was reported by Shimizu et al., 2002, who deduced thehydrophobic nature of the surface of TiO2-pillared montmorillonite ascompared with P25 by the competitive adsorption of benzene andphenol. The hydrophilicity of the TiO2 originates from the surfacehydroxyl groups. In the literature, it was conjectured that the surfacehydrophobicity of pillared montmorillonite was related to thedecrease in polarity of the clay mineral surface by exchange of cationsin the interlayer space with metal oxide pillar (Malla and Komarneni,1990; Zhu et al., 1995; Zhu and Yamanaka, 1997; Ooka et al., 2004).The observed selectivity enhancement of the pillaredmontmorillonitemay be explained as follows. The hydrophobic surface of Ti-montmorillonite is more accessible to unpolar hydrocarbons than tothe hydrophilic surface of TiO2. When the partially oxygenatedproduct (cyclohexene epoxide) is formed, the adsorption of thepolar products on the hydrophobic Ti-montmorillonite is inhibited byunpolar hydrocarbon, and the cyclohexene epoxide, resulting in itshigher selectivity. On the other hand, the products can be present onhydrophilic surface of TiO2, which will result in the over-oxidation toCO2.

3.2.3. Effect of Ti-montmorillonite concentrationWith all other experimental conditions the same, cyclohexene

epoxide yield increased with increasing TiO2-montmorillonite ratioup to 2.5 mg/mL, (Fig. 10). The maximum yield (45%) and selectivity(45%) of cyclohexene epoxide were obtained at 2.5 mg/mL Ti-montmorillonite. When the Ti-montmorillonite content increased,the number of adsorption sites per unit volume of dispersion alsoincreased, thus accounting for the increase in product formation.However, with increasing TiO2-montmorillonite content, the light

Fig. 8. The concentration of cyclohexene epoxide as a function of time in the photo-epoxidation of cyclohexene on Ti-montmorillonite and P25. Reaction conditions:cyclohexene 20 mL (10 mol/L), catalysts 50 mg (Ti-montmorillonite) or 15 mg (TiO2

P25), UV irradiation and oxygen flow rate 100mL/min.

Table 2Photo-epoxidation of cyclohexene catalyzed by Ti-montmorillonite.

Time (h) Yield (%) Epoxide selectivity (%)

4 29 426 39 438 45 4510 40 40

Reaction conditions: cyclohexene 20 mL, Ti-montmorillonite 50 mg, UV irradiation andoxygen flow rate 100 mL/min.

Fig. 10. Effect of Ti-montmorillonite concentration on the photo-epoxidation of

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penetration into the reaction medium decreased, negatively affectedthe apparent rate of reaction. A similar result was reported byKonstantinou and Albanis (2004).

cyclohexene. Reaction conditions: cyclohexene 20 mL, UV irradiation, reaction time 8 hand oxygen flow rate 100 mL/min.

3.2.4. Effect of solvent natureThe amounts of cyclohexene epoxide formed in 8 h in different

solvents are shown in Fig. 11. The highest formation rate ofcyclohexene epoxide was achieved in acetonitrile (the yield and theselectivity of epoxide cyclohexene were 25% and 39% respectively).Similar result was observed in Ding et al. (2004) report. However, asignificant formation of chlorocyclohexene was observed in carbontetrachloride, included in the desired products, the highest product-formation rate would have been obtained in carbon tetrachloride,along with cyclohexene epoxide yield and selectivity of 15% and 34%.This suggests that chlorine played a significant role in the photo-epoxidation reaction of cyclohexene on Ti-montmorillonite, leadingto significant product formation. The lowest product-formation rateswere observed in chloroform andmethylcyclohexane. The chloroformstrongly inhibited the cyclohexene epoxidation; very little cyclohex-ene epoxidation products (the yield and the selectivity of epoxidecyclohexene were 5% and 25% respectively) or chlorinated by-products were observed. Our data suggest that chloroform competesfor both the oxidation sites and the reduction sites, thus inhibiting theadsorption of both oxygen and cyclohexene on Ti-montmorillonite.Calza et al. (1997) also concluded that chloroform is degraded both byoxidation and reduction on irradiated titanium dioxide. The presenceof significant amounts of chlorocyclohexene in carbon tetrachloridesuggests that carbon tetrachloride does not compete with cyclohex-ene for oxidation sites, and that the degradation of carbontetrachloride occurs by reduction as concluded by Calza et al.(1997) who studied the photo-degradation of chloromethanes inaqueous dispersions of titanium dioxide. Acetonitrile was adsorbed toa significant extent onto the oxidation sites of the titanium dioxidesurface forming radicals, which in turn degraded cyclohexenemolecule.

In methylcyclohexane, the observed slow rate of product forma-tion (the yield and the selectivity of epoxide cyclohexene were 10%and 29% respectively) suggests that the methylcyclohexane waspreferentially adsorbed over cyclohexene, and therefore, reduced the

Fig. 9. Adsorption isotherms of cyclohexene on Ti-montmorillonite, Na-montmorilloniteand TiO2 P25.

number of active sites available for cyclohexene oxidation. We notethat all the reaction rates were lower than that of pure cyclohexene.

3.2.5. Epoxidation of higher olefinsUsing cyclooctene, 1-octene and 1-hexene instead of cyclohexene

under similar conditions (Table 3) a higher reactivity of cyclic olefinsand a lower reactivity of terminal olefins were observed (Valente et al.,2004), we have selected the reaction times in the range 4–8 h for cyclicolefins and 8–10 h for terminal ones to allow comparable transforma-tions. By-products were detected except for the epoxides. In thecyclohexene epoxidation, we observed 2-cyclohexene-1-ol with amaximum yield and selectivity of 6% and 10%, after 3 h; 2-cyclohex-ene-1-one and 1,2-cyclohexanediol were also detected with a maxi-mum yield of 7% and 9% respectively, and a maximum selectivity of 7%and 9%, after 10 h. In the cyclooctene epoxidation, we observed 2-cyclooctene-1-ol with a maximum yield and selectivity of 9% and 14%respectively, after 3 h; 2-cyclooctene-1-one and 1,2-cyclooctanediolwere also detected with a maximum yield of 11% and 12% respectively,and a maximum selectivity of 11% and 12% respectively, after 10 h.

A higher electron donating ability of the olefin double bond isexpected to facilitate the reaction. The order of increasing reactivitybased on epoxide yields was cyclooctene Ncyclohexene N1-hexeneN1-octene (Table 3). To explain this trend, the electronicand steric effects should be taken into consideration. The higherelectronic density of the double bond is expected to promote themore epoxidation. Therefore, cyclooctene and cyclohexene withdouble bonds between secondary carbon atoms should exhibit ahigher activity in comparison with 1-hexene and 1-octene whichcontain double bonds between secondary and primary carbon atoms.That 1-octene was epoxidized more slowly than 1-hexene wasrelated to the steric effect of the hexyl group connected to the double

Fig. 11. Epoxide formation (%) in various solventmedia. Reaction conditions: cyclohexene1 mL, solvent 20 mL, Ti-montmorillonite 50 mg, reaction time 8 h and oxygen flow rate100 mL/min.

Table 3Results of photocatalytic epoxidation of some olefins in the presence of Ti-montmorillonite.

Run number Substrate Time (h) Yield (%) Selectivity (%)

1 Cyclooctene 4 32 452 8 47 473 Cyclohexene 4 29 424 8 45 455 1-Hexene 8 21 386 10 32 427 1-Octene 8 13 318 10 22 37

Reaction conditions: olefin 20 mL, Ti-montmorillonite 50 mg, UV irradiation and oxygenflow rate 100 mL/min.

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bondwhich hinders more strongly the approach to the catalyst metalcenters compared with 1-hexene where double bond carries thesmaller butyl group.

4. Conclusion

Intercalation titanium species in montmorillonite yielded anefficient class of heterogeneous catalysts for photo-epoxidation ofcyclo-olefins and terminal olefins. Cyclohexene epoxide was formedas themajor product. Product yield and selectivity were dependent onthe irradiation period, pillaring process, TiO2-montmorillonite con-tent and nature of the solvent. Under optimized conditions, themaximum cyclohexene epoxide selectivity and yield were 45% and45%. TiO2-montmorillonite showed a higher selectivity to cyclohex-ene epoxide than TiO2 (P25), possibly because of the hydrophobicnature and the higher specific surface area of pillared montmorillon-ite. Electron-rich cyclic olefins were more active than the electron-poor terminal olefins.

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