Applied Catalysis A: General 205 (2001) 85–92

High selective catalyst CuCl/MCM-41 foroxidative carbonylation of methanol to dimethyl carbonate

Zhong Lia,∗, Kechang Xiea, Robert C.T. Sladeba Institute of Chemical Engineering for Coal, Taiyuan University of Technology, Taiyuan, Shanxi 030024, PR China

b Department of Chemistry, University of Exeter, Exeter, EX4 4QD, UK

Received 5 January 2000; received in revised form 14 March 2000; accepted 14 March 2000

Abstract

In this study, MCM-41 material was synthesised and the mesoporous structure was confirmed by powder XRD patterns.Organic group 3-chloropropyl was anchored on the surface of MCM-41(∞) by reaction of 3-chloropropyltrimethoxysilanewith terminal silanol groups on the surface of MCM-41(∞) material. The modified material MCM-41(∞)-Cl still kept itsmesoporous structure even after the material was calcined again at 550◦C for 4 h and the organic groups were removed.Prepared by solid state ion-exchange under flowing nitrogen, CuCl/MCM-41 catalyst had 100% selectivity of dimethylcarbonate based on methanol and 5–10 wt.% conversion of methanol at 130◦C. With the decreasing mole ratio of Si/Al ofMCM-41 material, e.g. increasing the aluminium content in the material, the catalytic activity increased because more CuI

was loaded on the material. When the reaction temperature increased, the dimethyl carbonate selectivity decreased and threeby-products: dimethyl ether, methyl formate, dimethoxymethane were formed at high temperature. Finally increasing theoxygen partial pressure in the feed gases resulted in more dimethyl carbonate formed. © 2001 Elsevier Science B.V. All rightsreserved.

Keywords:Oxidative carbonylation; Solid-state ion-exchange; CuCl, MCM-41; Dimethyl carbonate

1. Introduction

Dimethyl carbonate (DMC) is an important chemi-cal material in the chemical industry and in the motorfuel industry. It can be used as an intermediate to sub-stitute for highly toxic phosgene and dimethyl sulphatein many chemical processes owing to the presenceof two methyl groups and one carbonyl group in itsmolecule [1]. DMC has high oxygen content, a goodblending octane, low toxicity, and quick biodegrada-tion and it is expected to be used as a fuel additive togasoline on a large scale [2].

∗ Corresponding author. Tel.:+86-351-6018466;fax: +86-351-6041142.E-mail address:lizhong@public.ty.sx.cn (Z. Li).

Enichem Company has developed a one-step slurrybatch process to make DMC from methanol, car-bon monoxide and oxygen following the oxidativecarbonylation:

(1)

Cuprous chloride is used as catalyst and suspendedin methanol liquid phase during the reaction. Romanosuggested that the reaction has two steps: oxidationand reduction [1]:

CH3OH+12O2+CuCl → 2(CH3O–Cu)Cl+H2O (2)

0926-860X/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved.PII: S0926-860X(00)00546-9

86 Z. Li et al. / Applied Catalysis A: General 205 (2001) 85–92

(3)

The equipment corrosion (because of HCl releasedduring the reaction), difficult separation of catalystfrom the reaction mixture and catalyst deactivation arethe main disadvantages of this process. Ube Companyhas developed a two-step gas phase reaction processthat employs nitric oxide (NO) as a redox couplingagent for the formation of DMC following the reaction[3]:

CH3OH + 12O2 + 2NO → 2CH3ONO+ H2O (4)

(5)

The total reaction is the same as reaction (1). The firstoxidation (4) goes easily but the reduction (5) takeplace under a PdCl2–CuCl2/C catalyst. Using highlydangerous NO is the fatal weakness of this process.Therefore, developing a one-step gas-phase process tomake DMC directly from oxidative carbonylation ofmethanol is more desirable and economical than thetwo processes given above because this process canavoid their disadvantages.

Curuntt [4–6] had tested a number of catalystsfor the one-step gas-phase oxidative carbonylationof methanol to DMC. The catalysts were preparedby impregnating the active carbon or oxides (MnO,ZnO, TiO2, SiO2 and Al2O3) in methanol solution of[Cu(OCH3)(pyr)Cl]2 or/and CuCl2. All of the testedcatalysts deactivated quickly because of losing thechlorine and forming paratacamite [Cu2(OH)3Cl] onthe supports. The chlorine seems essential for thecatalyst because it can be partially regenerated bypassing diluted HCl gas over the catalyst to increasethe Cl/Cu ratio to approximately 1.2 (weight) whichis close to the Cl/Cu ratio of the fresh catalyst [5,6].The initial DMC productivity was about 0.1 LHSV ofDMC (liquid volume of DMC produced per volumeof reactor per hour) for the DARCO active carbonimpregnated catalyst. The selectivity of DMC basedon CO conversion (designated asSDMC/CO hereafter)was about 65% [5]. For the SiO2 and Al2O3 supports,

the reactivities were very low andSDMC/CO valueswere 40 and 60%, respectively. Wang et al. [7] studiedthe two metal catalysts of PdCl2–CuCl2 supported ona active carbon for one-step gas phase oxidative car-bonylation of methanol to DMC. The bimetallic cata-lyst had higher activity than the single metal catalystbut SDMC/CO was very low (26.4%) andSDMC/MeOH(selectivity of DMC based on methanol conversion)was 84.5%. Smith and Landau [8] had tested thehalogen-free catalysts made by ion-exchange of CuII

in a copper nitrate aqueous solution with a naturalsmectite clay or aluminium pillared interlayered clayfor one-step gas-phase oxidative carbonylation ofmethanol to DMC. When the reaction temperaturewas 120◦C, SDMC/CO and SDMC/MeOH were 51±4and 28±2%, respectively.

King [9,10] reported that the CuIY catalyst (al-most free of chlorine) made by the high temperaturesolid-state ion-exchange of CuCl with HY zeolite un-der flowing helium had higher and more stable activitythan those made by solution ion-exchange of CuCl2with the HY zeolite or impregnation of CuCl2 in theactive carbon. ButSDMC/MeOH is about 80%. The cata-lytic mechanism, which is similar to the Romanomechanism, was studied by in-situ FTIR as follows:

2CH3OH + 12O2 + 2Cu+Ze−

→ 2(CH3O–Cu)+Ze− + H2O (6)

(7)

(8)

Ze− denotes negative charge on zeolite frame work.The mechanism clearly shows that chlorine is not

required for the CuIY material to catalyse the oxidativecarbonylation of methanol to DMC.

Zeolite strongly adsorbed methanol in its cagesor channels and has strong acid sites which catalysemethanol to form by-products, such as methyl for-mate, methyl ether, etc. Mesoporous aluminosilicateMCM-41 is similar to zeolite in structure but it hasmesopores and low strength of acid sites [11]. In this

Z. Li et al. / Applied Catalysis A: General 205 (2001) 85–92 87

study it is shown that CuCl/MCM-41 material pre-pared by solid state ion-exchange has good activityand very high selectivity of DMC based on methanolconversion.

2. Experimental

2.1. Preparation of MCM-41 material

Aluminiumsilicate MCM-41 materials were syn-thesised according to the following procedure [11].A 25% solution of tetramethylammonium chloride(11.4 g) (TMACl, Aldrich) was combined with 7.42 gsodium silicate solution (∼14%NaOH,∼27%SiO2,

Aldrich), and 34.56 g of a 25% aqueous solutionof cetyltrimethylammonium bromide (Lancaster) ina 250 ml breaker with strong stirring. Then 4.06 gCAB-O-Sil M-5 fumed silica (BDH) with 20 g H2Owas added and the mixture was stirred strongly for2 h. If desired, a aqueous solution of Al2(SO4)3·6H2O(BDH) containing 15 g H2O was added into the gelvery slowly and the mixture was stirred for another1 h. Then the gel was transferred into a Teflon-bottleand kept at 100◦C for 70 h. The solid product wasfiltered, washed with distilled water, dried in air at100◦C for 20 h and finally calcined at 550◦C for 24 h.The materials are designated as MCM-41(X), whereX=10, 80 are the Si/Al ratios of the synthesis gel.The pure silicate material is designated as MCM-41(∞).

Two grams of MCM-41(∞) and 2 g of 3-chloropro-pyltrimethoxysilane (Lancaster) were added into 50 mlof toluene in a 100 ml flask. The mixture was heatedand fluxed for 4 h. Then the solid material was filtered,washed with 50 ml toluene two times and dried at am-bient temperature for 12 h and at 100◦C for 2 h. Thismaterial is designated as MCM-41(∞)-Cl.

2.2. Preparation of catalyst

A catalyst was made by heating a well physical mix-ture of CuCl (10 wt.%) with a MCM-41 material at aheating rate of 10◦C/min from ambient temperature to350◦C (but CuCl/MCM-41(∞)-Cl at 250◦C) and thenheld for 15 h under flowing dried nitrogen. After themixture was cooled to room temperature, 0.5 g catalystwas packed in a reactor tube and tested for its catalytic

property for oxidative carbonylation of methanol withcarbon monoxide and oxygen immediately.

2.3. Oxidative carbonylation of methanol

The gas phase oxidative carbonylation of methanolwith carbon monoxide and oxygen was carried out bya fixed bed reactor system with online gas-chroma-tography (GC) analysis. Carbon monoxide, oxygenand nitrogen gases were each passed through their in-dividual mass flow meter and controller (BronkhorstHI-TEC) and then mixed in a gas mixer before theygot into the fixed bed reactor. Carbon monoxide hadto pass through a methanol bubbler at 40◦C in orderto bring a constant flow of methanol into the reac-tor. The fixed-bed reactor furnace was controlled bya time-programmed controller (Eurotherm 2416). TheGC (Philips Scientific PU4400) took three samples ofthe product’s gas simultaneously and then analysedautomatically. A molecular sieve 13X A.T. packed co-lumn with TCD detector was used for O2, N2, COand H2 analysis, a Porapak-QS packed column withTCD detector for CO2, H2O and MeOH analysis anda CP Sil-5 CB capillary column with FID detector fororganic compounds analysis. High purity helium gaswas used as GC flow gas. The GC spectrum was anal-ysed by MIDAS software and the corrected-coefficientnormalisation method was used for the calculation.

2.4. Characterization

Powder XRD spectra were recorded by a computer-driven Philips step-scanning diffractometer with aPhilips PW1050/25 goniometer (Ni-filter, Cr Ka ra-diation, λ=2.2909 Å). Data were collected for 4 severy 0.01◦ of 2θ at 30 mA and 40 kV. TG/TGA andDTA analyses were carried out simultaneously on aStanton Redcroft STA-781 instrument. About 10 mgof sample was placed in a platinum pan and heatedfrom ambient temperature to 1200◦C at a heatingrate of 10◦C/min under flowing nitrogen or air witha flow rate of 50 ml/min. An internal standard ofa-alumina was used. FTIR spectra were produced ona Nicolet Magna-IR 550 spectrometer over the rangeof 400–4000 cm−1 with a solution of 4 cm−1 at roomtemperature. The sample was mixed with anhydrousKBr by mortar pestle and then pressed to a disc.

88 Z. Li et al. / Applied Catalysis A: General 205 (2001) 85–92

3. Results and discussion

3.1. Characterisation of MCM-41 materials andcatalysts

3.1.1. MCM-41 materialsMesoporous molecular sieve MCM-41 possesses a

hexagonal array of uniform mesopores of 15–100 Ådiameters [12]. Fig. 1 shows powder XRD patternsof as synthesised, calcined MCM-41(∞) and calcinedMCM-41(80) which correspond to MCM-41 mate-rial XRD pattern as described by Beck et al. [12].MCM-41(∞) as synthesised had ad100 of 61.9 Å fromXRD pattern but after being calcined at 550◦C for 24 h,the template was removed and thed100 was reducedto 34.6 Å. For the calcined MCM-41(80) material, thed100 was 35.8 Å.

MCM-41(∞) contains 27 interior silanol groupsSiOH per 100 Si atoms which behave non-acidically;the IR vibration band at 3740 cm−1 belongs to the re-active isolated terminal silanol groups [13]. The resultsof TG/TGA and DTA analysis of MCM-41(∞) afterbeing calcined at 550◦C for 24 h are shown in Fig. 2.Water physisorbed and hydrogen-bonded on MCM-41(∞) material was lost up to 200◦C. The mass lossbetween 200 and 1000◦C was the result of dehydro-xylation of silanol groups on MCM-41(∞) surface toform removable water, from which 25 interior silanolgroups SiOH per 100 Si atoms were calculated.The isolated terminal silanol group was also observedas the FTIR spectrum vibration band at 3744 cm−1

(Fig. 3a). FTIR spectrum b in Fig. 3 shows that

Fig. 1. XRD patterns of MCM-41 materials. (a) MCM-41(∞)as synthesised; (b) MCM-41(∞) calcined and (c) MCM-41(80)calcined.

Fig. 2. TG/TGA and DTA analysis of calcined MCM-41(∞) underflowing air at a heating rate of 10◦C/min.

the terminal silanol groups SiOH vibration band at3744 cm−1 disappeared and new vibration bands at1240, 919 and 700 cm−1 that are associated with Si–Cvibrations were present. It is clear that 3-chloropropyl-trimethoxysilane was connected with the terminalsilanol groups of the MCM-41(∞). The TG/TGA withDTA analysis of MCM-41(∞)-Cl are given in Fig. 4.If the ash is considered as SiO2 and all mass loss isdue to the organic decomposition, then 11 of 100 Siatoms reacted with 3-chloropropyltrimethoxysilaneto anchor the organic groups on the surface ofMCM-41(∞) material. MCM-41(∞)-Cl material be-gan to decompose its organic group at 320◦C, asobserved by the TG/TGA in Fig. 4. The powder XRDpatterns of synthesised MCM-41(∞)-Cl material andof that calcined at 550◦C for 5 h in air are shownin Fig. 5. This result confirms that the mesoporousstructure was not destroyed in synthesised MCM-41(∞)-Cl or in the calcined MCM-41(∞)-Cl and thatthe pore size remained almost unchanged.

3.1.2. CatalystsThe results of TG/TGA and DTA analysis of a phys-

ically mixed 10% CuCl/MCM-41(∞) mixture underflowing nitrogen are given in Fig. 6. The first massloss peak around 80◦C was due to a loss of physi-cally adsorbed water in MCM-41(∞) material. Thesecond peak around 325◦C resulted from the reactionof CuCl with silanol group SiOH on the surface ofMCM-41(∞) to form Si–O−Cu+ and to release HClgas as the by-product. The TG/TGA analysis of pureMCM-41(∞) in Fig. 2 does not show there is a massloss around 325◦C and pure CuCl thermal gravimet-

Z. Li et al. / Applied Catalysis A: General 205 (2001) 85–92 89

Fig. 3. FTIR spectra of (a) calcined MCM-41(∞) and (b) synthesised MCM- 41(∞)-Cl.

ric analysis shows that its massive mass loss beganfrom 400◦C under flowing nitrogen at a heating rateof 10◦C/min. In our previous work [14], it was provedthat the solid-state ion-exchange of CuI in solid CuClwith H+ in HY zeolite happened around 320◦C butthe reaction of CuCl with silanol group on the HYzeolite surface occurs at high temperatures beyond650◦C. Therefore, it seems that the silanol group onthe surface of MCM-41(∞) material is more likely toreact with CuCl than the silanol group of HY zeolite.Like the ion-exchanged CuI in HY zeolite as the ac-tive site [9,10], the loaded CuI of MCM-41(∞) is theactive site to catalyse the oxidative carbonylation ofmethanol to DMC. The mass loss around 630◦C wasdue to sublimation of CuCl.

Fig. 4. TG/TGA and DTA analysis of synthesised MCM-41(∞)-Clunder flowing air at a heating rate of 10◦C/min.

Fig. 5. XRD patterns of (a) MCM-41(∞)-Cl and (b) calcinedMCM-41(∞)-Cl.

Fig. 6. TG/TGA and DTA analysis of 10% CuCl/MCM-41(∞)under flowing nitrogen at a heating rate of 10◦C/min.

90 Z. Li et al. / Applied Catalysis A: General 205 (2001) 85–92

Fig. 7. Powder XRD patterns of (a) CuCl/MCM-41(∞) and (b)CuCl/MCM-41(80) after the heating treatment at 350◦C for 15 hunder flowing nitrogen.

Powder XRD patterns of 10% CuCl/MCM-41(∞)and 10% CuCl/MCM-41(80) after heating treatment at350◦C for 15 h under flow of dried nitrogen are shownin Fig. 7. MCM-41(∞) still kept its mesoporous struc-ture but MCM-41(80) lost some mesoporous structure.It is observed that some Cu2OCl2 phase (2θ=24.31)was formed and very little CuCl phase (2θ=43.11) wasleft on the surface of MCM-41(∞) material. Most ofthe CuCl in the mixture was sublimated and went offwith the flowing nitrogen during the heating treatment.

3.2. Oxidative carbonylation of methanol

3.2.1. Influence of MCM-41 supportsThe catalytic results of CuCl/MCM-41 catalysts

on oxidative carbonylation of methanol with COand O2 are given in Table 1. The pure MCM-41(∞)

Table 1The influence of Si/Al on CuCl/MCM-41 catalysta

Catalyst Si/Al(mol)

Conversion ofMeOH (wt.%)

SDMC/MeOH

(mol)

MCM-41(∞) ∞ – –CuCl/MCM-41(∞)b ∞ 2.06 100CuCl/MCM-41(80)b 80 2.47 100CuCl/MCM-41(10)b 10 5.45 100CuCl/MCM-41(∞)-Clc ∞ – –

a Reaction condition: CO: 5 ml/min, CO/MeOH (mol)=16, CO/O2 (mol) =10, temperature 130◦C.

b 10% CuCl/MCM-41 heated at 350◦C for 15 h under flowingN2.

c 10% CuCl/MCM-41(∞)-Cl heated at 250◦C for 15 h underflowing N2.

did not have any catalytic activity. The conversionof methanol on CuCl/MCM-41 catalysts increasedas the mole ratio of Si/Al decreased; the mole se-lectivity of DMC based on methanol conversion(SDMC/MeOH) for all the tested catalysts are 100%. Noby-product was detected during the catalytic process.For CuCl/MCM-41(∞)-Cl catalyst, no DMC productor by-products was detected at this catalytic condi-tion. Catalyst CuCl/MCM-41(∞) treated at 350◦Cfor 15 h under flowing nitrogen was loaded CuI asSi–O−Cu+ as described in Section 3.1.2. This CuI

site was the catalytic active centre for the oxidativecarbonylation of methanol to DMC. The very smallamount of CuCl existing on the CuCl/MCM-41(∞)material as observed in the powder XRD pattern(Fig. 7) was not the effective active centre. If itwas, the catalyst CuCl/MCM-41(∞)-Cl should havea higher activity than CuCl/MCM-41(∞) becauseCuCl/MCM-41(∞)-Cl material was prepared at alower temperature 250◦C and should have more CuClleft than CuCl/MCM-41(∞). On the other hand, thereactive terminal silanol group SiOH on the surfaceof MCM-41(∞)-Cl was not present and could notform Si–O−Cu+ site. Moreover, it was consideredthat, if the extra chlorine atoms on the surface ofthe MCM-41(∞)-Cl material are fixed, the catalystshould have high activity because loss of chlorineduring the catalytic oxidative carbonylation made theimpregnated CuCl2 supported on active carbon cat-alyst to deactivate [5,6]. Therefore, it is concludedthat Si–O−Cu+ is the active catalytic centre on theCuCl/MCM-41(∞) catalyst.

With the mole ratio of Si/Al decreasing, more alu-minium atoms were introduced into the frameworkstructure of MCM-41 and more CuI ions in solid stateCuCl were exchanged with Na+ in MCM-41 mate-rial. The ion-exchanged CuI also is the active centrefor oxidative carbonylation of methanol to DMC asCuI ion-exchanged into zeolite [9,10]. Therefore,the catalytic activity of CuCl/MCM-41 catalysts wasincreased with the mole ratio of Si/Al increasingin the support MCM-41. Compared to the zeolitesupported catalysts, the reason of the high selecti-vity of DMC (SDMC/MeOH) of MCM-41 supportedcatalyst is partially that the mesoporous structuremakes the adsorption of methanol on the surface ofMCM-41 material weak and the desorption of DMCeasy.

Z. Li et al. / Applied Catalysis A: General 205 (2001) 85–92 91

Table 2the influence of reaction temperature on CuCl/MCM-41(10)a

Temperature(◦C)

Conversion ofMeOH (wt.%)

SMeOH/DMC

(mol)

100 1.18 100110 1.80 100120 2.66 100130 5.46 100140 6.01 63.3150 5.45 51.6180 10.63 10.1

a Note: Catalyst:CuCl/MCM-41(10); reaction: CO: 5 ml/min,CO/MeOH (mol)=16, CO/O2 (mol)=10, staying 4 h at each tem-perature.

3.3. Influence of the reaction temperature

Table 2 gives results of reaction temperature in-fluence on the conversion of MeOH andSDMC/MeOHand Table 3 gives composition of organic products.When the reaction temperature was below 130◦C, theconversion of methanol increased with the tempera-ture andSDMC/MeOH was 100%. When the reactiontemperature exceeded 130◦C, DMC content of theproducts reduced and by products were formed. TheSDMC/MeOH was reduced to 10.1% when the reactiontemperature became 180◦C. From the GC analysis,only three by-products were observed: dimethyl ether,methyl formate and dimethoxymethane. Therefore, thefollowing side reactions are the competitive reactionsof oxidative carbonylation of methanol to DMC:

2CH3OH → CH3OCH3 + H2O (9)

2CH3OH + CH2O → CH3OCH2OCH+ H2O (10)

CH3OH + HCOOH→ HCOOHCH3 + H2O (11)

The CH2O and HCOOH come from the oxidation of

Table 3Composition of the organic productsa

Temperature(◦C)

CH3OCH3

(wt.%)HCOOCH3

(wt.%)CH3OCH2

OCH3

(wt.%)

DMC(wt.%)

140 0.69 – 0.75 4.57150 0.89 – 0.95 3.61180 4.23 1.65 2.94 1.81

a Note: Reaction conditions in Table 2.

Table 4Composition of the organic productsa

Temperature(◦C)

CH3OCH3

(wt.%)HCOOCH3

(wt.%)CH3OCH2

OCH3

(wt.%)

DMC(wt.%)

130 – – – –140 – – – –155 – – 0.23 –170 – – 0.26 –185 – 0.40 1.03 0.64200 – 0.80 1.32 1.08

a Note: (a) Catalyst: 10% CuCl/MCM-41(∞)-Cl; (b) reaction:CO: 5 ml/min, CO/MeOH (mol)=16, CO/O2 (mol)=10, tempera-ture rising at 0.5◦C/min.

Table 5The influence of CO/O2 on CuCl/MCM-41(10) catalysta

O2

(l/min)CO/O2

(mol)Conversion ofMeOH (wt.%)

SDMC/MeOH (mol)

0.5 8 5.45 1001.0 4 6.68 1002.0 2 7.25 1004.0 1 9.06 100

a Note: (a) Catalyst: 20%CuCl/MCM-41(10); (b) reaction: CO:4.0 ml/min, CO/MeOH (mol)=16, temperature 130◦C.

methanol:

CH3OH + 12O2 → CH2O + H2O (12)

CH2O + 12O2 → HCOOH (13)

For CuCl/MCM-41(∞)-Cl catalyst, DMC was founduntil the reaction temperature rose to 185◦C (Table 4)and dimethoxymethane by-product was more thanDMC in the products.

3.3.1. Influence of mole ratio of CO/O2The result of the influence of mole ratio of CO/O2

on the catalysis is given in Table 5. With the moleratio of CO/O2 reduced, e.g. increasing oxygen partialpressure, the conversion of methanol increased and theSDMC/MeOH was still 100%.

4. Conclusions

MCM-41 material was synthesised and the meso-porous structure was confirmed by powder XRD pat-terns. Twenty-five of 100 Si atoms in MCM-41(∞)material were found to exist as silanol by TG/TGA

92 Z. Li et al. / Applied Catalysis A: General 205 (2001) 85–92

analysis. The terminal silanol was more reactive thanHY zeolite, easily forming Si–O−Cu+ with solid stateCuCl during heating treatment at 350◦C under flowingnitrogen. The Si–O−Cu+ is the catalytic active cen-tre for oxidative carbonylation of methanol to DMC.Organic group 3-chloropropyl can be anchored on thesurface of MCM-41(∞) by the reaction of 3-chlo-ropropyltrimethoxysilane with terminal silanol groupson the surface of MCM-41(∞) material. After the re-action, the material still kept its mesoporous structureeven when it was calcined again at 550◦C for 4 h andthe organic groups were removed. MCM-41(∞)-Clmaterial decomposed its organic groups at 320◦C.Prepared by heating treatment under flowing nitro-gen, CuCl/MCM-41 catalyst had a 100% selectivityof DMC based on conversion of methanol; the con-version of methanol was around 5–10 wt.%. With themole ratio of Si/Al of MCM-41 material decreasing,e.g. the aluminium content in the material increasing,the catalytic activity increased because more CuI wasloaded on the material by solid-state ion-exchange.With the reaction temperature increasing, the se-lectivity was decreased because three by-products:dimethyl ether, methyl formate, dimethoxymethanewere formed at high temperature. Finally, increasingthe oxygen partial pressure resulted in more DMCbeing formed.

Acknowledgements

We thank the Taiyuan University of Technology,China, and Universities’ China Committee in London

for financial support on Prof. Li’s academic visit andwe also thank all the members of the Material Che-mistry Research Group and Department of Chemi-stry, University of Exeter, UK, for their friendlysupport.

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