SYNTHESIS, CHARACTERIZATION AND ACTIVITY OF Al-MCM...

SYNTHESIS, CHARACTERIZATION AND ACTIVITY OF Al-MCM-41

CATALYST FOR HYDROXYALKYLATION OF EPOXIDES

AZMI BIN MOHAMED

UNIVERSITI TEKNOLOGI MALAYSIA

SYNTHESIS, CHARACTERIZATION AND ACTIVITY OF Al-MCM-41

CATALYST FOR HYDROXYALKYLATION OF EPOXIDES

AZMI BIN MOHAMED

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Master of Science (Chemistry)

Faculty of Science

Universiti Teknologi Malaysia

APRIL 2005

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Dedication to my beloved father, mother, family and friends…

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ACKNOWLEDGEMENT

First of all, in a humble way I wish to give all the Praise to Allah, the

Almighty God for with His mercy has given me the strength, keredhaanNya and time

to complete this work.

I am deeply indebted to Prof. Dr Halimaton Hamdan, my Supervisor, for her

patience, supervision, encouragement and thoughtful guidance towards the

completion of this thesis. I wish to express special appreciation to Assoc. Prof. Dr

Salasiah Endud, Assoc. Prof Dr. Zainab Ramli, Assoc. Prof. Mohd Nazlan Mohd

Muhid and Dr. Hadi Nur for their kindness and support. I also want to thank to all

my colleagues in Zeolite and Porous Material Group for their help, support, interest

and valuable hints.

I am particularly grateful to Ibnu Sina Institute For Fundamental Science

Studies, Department of Chemistry, Faculty of Science Universiti Teknologi Malaysia

and Majlis Amanah Rakyat (MARA) for all facilities, study leave and financial

support .

Lastly, I would like to acknowledge my family; whose patient love enabled

me to complete this research. Thank you.

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ABSTRACT

Perfumery chemicals and intermediates are produced on a large scale by Friedel Crafts alkylation or acylation of aromatic compounds in the presence of Lewis acid catalyst. However, problem in the industrial process of perfumery chemical and intermediate manufacture like toxity, corrosivity and production of pollutants, make convenient to change the conventional Lewis acid AlCl3 or FeCl3 catalysts by acid solid catalyst. Thus, Al-MCM-41 catalysts were prepared with various SiO2:Al2O3 ratios via direct and secondary syntheses using sodium aluminate as the aluminium source. Al-MCM-41 was characterized by X-ray Diffraction (XRD), Surface Area Analyzer Instrument and Fourier Transform Infrared Spectroscopy (FTIR). The results indicate that Al-MCM-41 sample with a uniform hexagonal pore structure and high surface area was synthesized. Structural studies by 27Al and 29Si MAS NMR spectroscopy indicated that Al are in the tetrahedral form and located in the framework. The presence of distorted framework aluminium was also observed, more significantly in the secondary aluminated samples. Maximum amount of Al was incorporated by direct synthesis with SiO2:Al2O3 ratio of 10 and a calculated Si/Al ratio of 15.2. Acidity studies using Pyridine Desorption Measurement and Temperature Programmed Desorption of Ammonia (TPD-NH3) show that the acidity of Al-MCM-41 increases with increase in Al incorporation into the MCM-41 framework. The potential of H-Al-MCM-41; as a heterogeneous catalyst was studied in the hydroxyalkylation of benzene with propylene oxide as a model reaction. Favourable reaction conditions such as SiO2:Al2O3 ratios, temperature, time on stream, the reactant mole ratio and solvent have significant influence on the distribution of products. Gas chromatography analysis indicates that H-Al-MCM-41 with SiO2:Al2O3 ratio of 10 demonstrates the highest catalytic activity with a conversion of benzene and selectivity of 92.3% and 87.5% respectively. The formation of 2-phenyl-1-propanol was favourable occurred at a temperature of 393 K after 24 hours with propylene oxide to benzene mole ratio of 0.5 using nitrobenzene as the solvent. The activity enhancement for catalyst is associated with the presence of distorted tricoordinated aluminium as Lewis acid sites. The strength of Lewis acid sites was correlated to appropriate aluminium content, temperature, B/L ratio, crystallinity and surface area of sample which played a role in order to improve catalytic activity of Al-MCM-41. Aprotic dipolar solvent such as nitrobenzene stabilized the unstable intermediate of propoxy cations to prevent propylene oxides oligomerisation. The results indicate that instead of aluminium content, solvent and reactant mole ratio also play a role to give high conversion and selectivity of 2-phenyl-1-propanol.

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ABSTRAK

Bahan kimia dan perantaraan pewangi biasanya dihasilkan pada skala yang besar melalui tindak balas pengalkilan dan pengasilan sebatian aromatik dengan mangkin asid Lewis. Masalah yang timbul dalam proses industri pengeluaran bahan kimia dan perantaraan pewangi seperti ketoksikan, kakisan dan penghasilan sisa adalah bertepatan dengan menggantikan mangkin asid Lewis konvensional AlCl3 atau FeCl3 kepada mangkin pepejal berasid. Maka, mangkin Al-MCM-41 disediakan dengan pelbagai nisbah SiO2:Al2O3 melalui sintesis terus dan sekunder menggunakan natrium aluminat sebagai sumber aluminium. Al-MCM-41 telah dicirikan menggunakan teknik Pembelauan Sinar-X (XRD), Analisis Luas Permukaan dan Spektroskopi Inframerah. Keputusan menunjukkan Al-MCM-41 mempamerkan struktur liang heksagon yang seragam dengan luas permukaan yang tinggi. Kajian struktur oleh Spektroskopi 27Al dan 29Si Putaran Sudut Ajaib-Resonans Magnet Nukleus (PSI-RMN) menunjukkan aluminium hadir dalam bentuk tetrahedral dan terletak dalam rangka struktur. Kehadiran rangka struktur aluminium terherot juga dapat diperhatikan lebih signifikan dalam sampel sintesis secara sekunder. Kandungan maksimum aluminium memasuki bingkaian dipamerkan oleh sampel dengan nisbah SiO2:Al2O3 bersamaan 10 dan Si/Al dihitung bersamaan 15.2. Kajian keasidan dijalankan menggunakan Penjerapan Piridina dan Penyahjerapan Ammonia Suhu Teraturcara (TPD-NH3) menunjukkan keasidan Al-MCM-41 meningkat dengan penambahan aluminium ke dalam bingkaian MCM-41. Maka, potensi mangkin H-Al-MCM-41 dalam tindak balas Friedel-Crafts diuji ke atas tindak balas penghidroksialkilan benzena dengan propilena oksida sebagai tindak balas model. Taburan hasil tindak balas didapati bergantung kepada keadaan terbaik tindak balas seperti nisbah SiO2:Al2O3, suhu tindak balas, masa tindak balas, nisbah mol reaktan dan pelarut. Analisis kromatografi gas menunjukkan H-Al-MCM-41 dengan nisbah SiO2:Al2O3 bersamaan 10 mempamerkan aktiviti permangkinan yang tinggi dengan darjah penukaran benzena dan kepilihan masing-masing 92.3% dan 87.5%. 2-fenil-1-propanol terhasil pada kadar terbaik pada suhu 393 K selepas 24 jam dengan nisbah mol propilena oksida kepada benzena bersamaan 0.5 dengan nitrobenzena sebagai pelarut. Peningkatan aktiviti permangkinan sampel ini dikaitkan dengan kehadiran aluminium trikoordinatan terherot sebagai tapak asid Lewis. Kekuatan tapak asid Lewis dikaitkan dengan kandungan aluminium, suhu, nisbah B/L, kehabluran dan luas permukaan sampel yang berperanan meningkatkan aktiviti permangkinan Al-MCM-41. Pelarut dwipolar aprotik seperti nitrobenzena dapat menstabilkan bahan perantaraan ion propoksi bagi mengelakkan pengoligomeran propilena oksida. Keputusan menunjukan selain daripada kandungan aluminium dalam sampel, pelarut dan nisbah reaktan juga memainkan peranan dalam meningkatkan darjah penukaran dan kepilihan 2-fenil-1-propanol.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

ACKNOWLEDGEMENT iv

ABSTRACT v

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xiii

LIST OF SYMBOLS xvii

LIST OF APPENDICES xviii

1 INTRODUCTION

1.1 General Introduction 1

1.2 Research Background 2

1.3 Problem Statement 3

1.4 Research Objectives 5

1.5 Scope of Study 5

2 LITERATURE REVIEW

2.1 Friedel Crafts Alkylation of Aromatic Compounds 6

2.2 Mesoporous Materials 8

2.2.1 Mesoporous MCM-41 Molecular Sieves 8

2.2.2 Mechanisms of Formation for MCM-41 11

2.3 Incorporation of Aluminium into MCM-41 12

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2.4 Catalytic Applications of MCM-41 15

2.5 Characterization Techniques

2.5.1 Fourier Transform Infrared Spectroscopy 16

2.5.2 Powdered X-ray Diffraction Measurement 17

2.5.3 Magic Angle Spinning-Nuclear Magnetic

Resonance (MAS NMR) Spectroscopy 19

2.5.4 Nitrogen Adsorption and Desorption

Measurement 21

2.6 Surface Acidity Measurement

2.6.1 Temperature Programmed Desorption of

Ammonia (TPD-NH3) 22

2.6.2 Pyridine Adsorption – Fourier Transformed

Infrared Spectroscopy Measurement 23

2.7 Quantitative Analysis of Hydroxyalkylation of

Benzene with Propylene Oxide 25

3 EXPERIMENTAL

3.1 Synthesis of Mesoporous MCM-41 27

3.1.1 Synthesis of Purely Siliceous MCM-41

(Si-MCM-41) 27

3.1.2 Synthesis of Aluminated MCM-41

(Al-MCM-41) 28

3.1.3 Preparation of H-Al-MCM-41 29

3.2 Characterization of Mesoporous MCM-41

3.2.1 X-ray Diffraction Measurement 30

3.2.2 Surface Area Measurement 30

3.2.3 Fourier Transform Infrared Spectroscopy 30

3.2.4 Solid State Nuclear Magnetic Resonance

Spectroscopy 31

3.3 Acidity Studies of Mesoporous MCM-41

3.3.1 Temperature Programmed Desorption of

Ammonia 31

3.3.2 Pyridine Adsorption – Fourier Transformed

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Infrared Spectroscopy Measurement 32

3.4 Catalytic Activity of Mesoporous MCM-41 in

Hydroxyalkylation of Benzene with Propylene Oxide

3.4.1 Activation of Catalysts 32

3.4.2 Catalytic Reaction Procedure 33

3.5 Most Favourable Condition of Model Reaction 34

3.5.1 SiO2:Al2O3 Ratio 34

3.5.2 Temperature 34

3.5.3 Time on Stream 34

3.5.4 Reactant Mole Ratio Composition 34

3.5.5 Solvent 36

3.5.6 Autoclave Reactor 36

3.6 Reusability of Catalysts 36

3.7 Characterization of Hydroxyalkylation of Benzene 36

with Propylene Oxide Reaction

4 RESULTS AND DISCUSSION

4.1 X-ray Diffraction Analysis 38

4.2 Fourier Transformed Infrared Spectrum Analysis 43

4.3 Magic Angle Spinning Nuclear Magnetic Resonance

(MAS NMR)

4.3.1. 27Al MAS NMR 47

4.3.2 29Si MAS NMR 49

4.4 Nitrogen Adsorption and Desorption Analysis 53

4.5 Pyridine Adsorption – Fourier Transformed Infrared

Spectroscopy Measurement 54

4.6 Temperature Programmed Desorption of Ammonia

(TPD-NH3) 61

4.7 Catalytic Activity of Mesoporous MCM-41 in

Friedel Crafts Reaction 63

4.8 Determination of Amount of Desired Product

(2-phenyl-1-propanol) 65

4.9 Effect of SiO2 : Al2O3 Ratios 66

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4.10 Effect of Temperature 68

4.11 Effect of Propylene Oxide : Benzene Mole Ratio 70

4.12 Effect of Reaction Time 71

4.13 Effect of Solvent 73

4.14 Effect of Autogenous Pressure 74

4.15 Reusability of Al-MCM-41 75

4.16 Proposed Mechanism of Hydroxyalkylation

of Benzene with Propylene Oxide Catalyzed

Al-MCM-41 78

5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions 81

5.2 Recommendations 83

REFERENCES 84

APPENDICES 91

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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Type of M41S mesoporous material 9

3.1 Sample Codes for Al-MCM-41 with different

SiO2: Al2O3 ratios 29

3.2 Operation Parameters for Gas Chromatography Flame

Ionization Detector (GC-FID) 37

3.3 Operation Parameters for Gas Chromatography-Mass

Spectroscopy (GC-MS) 37

4.1 The degree of crystallinity of samples with various

SiO2:Al2O3 ratios 40

4.2 Some properties of Si-MCM-41 and Al-MCM-41 42

4.3 Wave number (cm-1) of IR spectra of Al-MCM-41

samples with various SiO2:Al2O3 ratios 45

4.4 Quantitative peak intensities of 27Al MAS NMR of

Al-MCM-41 samples 49

4.5 Calculated peak distribution and Si/Al ratio from 29Si MAS NMR 51

4.6 Surface properties of Al-MCM-41 with various

SiO2:Al2O3 ratios 54

4.7 Number of acid sites (µmol pyridine g-1) in

H-Al-MCM-41 samples 60

4.8 Ratio of Brønsted (B) to Lewis (L) acidity in the

H-Al-MCM-41samples at different desorption temperatures 60

4.9 Amount gas adsorbed of various H-Al-MCM-41 61

4.10 Gas Chromatography data for hydroxyalkylation of

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propylene oxide with benzene 63

4.11 The effect of temperature on the conversion and yield of

desired product using Dir-Al-MCM-41 (10) at constant

parameter (Reactant Mole Ratio: 0.5; Time: 24 hours;

Solvent: Nitrobenzene) 69

4.12 Effect of propylene oxide : benzene mole ratio on

hydroxyalkylation of benzene with propylene oxides over

Dir-Al-MCM-41 (10) at constant parameter (Temperature:

393 K; Time: 24 hours; Solvent: Nitrobenzene) 70

4.13 Effect of solvent on hydroxyalkylation of benzene with

propylene oxides over Dir-Al-MCM-41 (10) at constant

parameter (Temperature: 393 K; Reactant Mole Ratio:

0.5; Time: 24 hours) 74

4.14 Effect of autogenous pressure on hydroxylakylation of

benzene with propylene oxide at 393 K over

Dir-Al-MCM-41(10) at constant parameter

(Temperature: 393 K; Reactant Mole Ratio: 0.5; Time:

24 hours; Solvent: Nitrobenzene) 75

4.15 Reusability of Dir-Al-MCM-41 (10) at 393 K at

constant parameter (Temperature: 393 K; Reactant Mole

Ratio: 0.5; Time: 24 hours; Solvent: Nitrobenzene) 76

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 The mesoporous M41S family [30] 10

2.2 The structure of mesoporous MCM-41 material [33] 10

2.3 (1) Liquid crystal phase initiated and (2) silicate anion

initiated [34] 11

2.4 Schematic presentation on the generation of Brønsted and

Lewis acid sites with (a) Distorted framework

Tricoordinated Aluminium (b) Extraframework Aluminum

(EFAL) in Al-MCM-41 14

2.5 FTIR spectrum for purely siliceous Si-MCM-41 [53] 18

2.6 Graphical representation of the Bragg equation. The

diffraction of x-rays is interpreted as the reflection on

a set of planes ( h k l ) [51] 18

2.7 29Si chemical shifts of Qn units in solid silicates [54] 20

2.8 The most frequently found types of gas physisorption

isotherms: na = amount adsorbed, ms = mass of solid

adsorbent, p = equilibrium pressure, p0 = saturation

vapour pressure [56] 22

2.9 Structure of (a) Pyridine and (b) Pyridinium Ion 23

3.1 Experiment set up for catalytic testing 33

3.2 Flow chart of determining the most favourable procedure

for propylene oxide and benzene 35

4.1 XRD powder pattern of (a) calcined at 823 K (b)

as synthesized Si-MCM-41 39

4.2 XRD powder pattern of Dir-Al-MCM41 (10) of

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(a) calcined (b) as synthesized samples 39

4.3 XRD powder pattern of Al-MCM-41 with various

(SiO2:Al2O3) ratios 41

4.4 XRD powder pattern of Sec-Al-MCM41 (0.25M)

(a) calcined at 823 K (b) before calcination at 823 K 42

4.5 FTIR spectra of Si-MCM-41 (a) after (b) before

calcination at 823 K 44

4.6 FTIR spectra of Sec-Al-MCM-41 (a) after (b) before

calcination at 823 K 44

4.7 FTIR spectra of calcined Al-MCM-41 with various

SiO2:Al2O3 ratios : (a) 10 (b) 20 (c) 40 (d) 80 46

4.8 27Al MAS NMR spectra of Zeolite A and Al-MCM-41

samples with various SiO2:Al2O3 ratio 48

4.9 29 Si MAS NMR spectra of Si-MCM-41 and Al-MCM-41

with various SiO2:Al2O3 ratio 50

4.10 Nitrogen adsorption isotherm of (a) Dir-Al-MCM41 (10)

(b) Sec-Al-MCM41(0.25 M) 52

4.11 FTIR spectra of hydroxyl region of Dir-Al-MCM41

with SiO2:Al2O3 (a) 10 (b) 20 (c) 40 (d) 80 dehydrated

at 673K under 10-5 mbar pressure 55

4.12 FTIR spectra of hydroxyl region of Sec-Al-MCM41(0.25 M)

with dehydrated at 673K under 10-5 mbar pressure 55

4.13 FTIR spectra of pyridine desorbed on Dir-Al-MCM41 (10)

under vacuum 10-5 mbar pressure at (a) 298K (b) 423K

(c) 523K (d) 673K for every 1 hour 56










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4.17 FTIR spectra of pyridine desorbed on Sec-Al-MCM-41

(0.25M) under vacuum 10-5 mbar pressure at (a) 298K

(b) 423K (c) 523K (d) 673K for every 1 hour 58

4.18 Temperature Programmed Desorption of Ammonia

(TPD-NH3) spectra of H-Al-MCM-41 of Dir-Al-MCM41

of (a) 10 (b) 20 (c) 40 (e) 80 (d) Sec-Al-MCM-41(0.25M) 62

4.19 Chromatogram of liquid product hydroxyalkylation of

benzene with propylene oxide without catalyst at 363 K 64

4.20 Chromatogram of liquid product hydroxyalkylation of

benzene with propylene oxide using Dir Al-MCM41 (10)

at 363 K after 3 hours 64

4.21 Calibration Curve of Standard with Internal Standard

(Toluene 2.0 M in Nitrobenzene) 65

4.22 Conversion of benzene and Selectivity of product (%)

with various SiO2:Al2O3 ratio at constant parameter



4.23 Amount of 2-phenyl-1-propanol (desired product) (mmol)

with various SiO2:Al2O3 ratio at constant parameter



4.24 Effect of temperature on the conversion and selectivity

of product using Dir-Al-MCM41 (10) at constant

parameter (Reactant Mole Ratio: 0.5; Time: 24 hours;


4.25 The effect of reaction time on benzene conversion over

Dir-Al-MCM-41 (10) at constant parameter (Temperature:

393 K; Reactant Mole Ratio: 0.5; Solvent: Nitrobenzene) 72

4.26 The effect of reaction time on selectivity and oligomerisation

of propylene oxides over Dir-Al-MCM-41 (10) at constant

parameter (Temperature: 393 K; Reactant Mole Ratio: 0.5;


4.27 X-ray diffractogram patterns of H-Dir-Al-MCM41 (10)

during three recycles 77

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4.28 Proposed mechanism for Al-MCM-41 catalyzed

hydroxyalkylation of aromatics with propylene oxides 79

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LIST OF SYMBOLS

B/L ratio - Brønsted acid sites to Lewis acid sites ratio

BET - Brunnauer, Emmett and Teller

Cu Kα - X-ray diffraction from Copper K energy levels

FTIR - Fourier Transform Infrared Spectroscopy

GC-MS - Gas Chromatography- Mass Spectroscopy

h - Hour

IS - Internal Standard

IUPAC - International Union of Pure and Applied Chemistry

KBr - Potassium Bromide

MAS NMR - Magic-Angle-Spinning Nuclear Magnetic Resonance

N2 - Nitrogen

OH - Hydroxyl

P/Po - Relative pressure; obtained by forming the ratio of the

equilibrium pressure and vapour pressure Po of the adsorbate

at the temperature where the isotherm is measured

SiO2: Al2O3 - Silica to Alumina ratio

SiO4 - Siliceous; framework silicon in zeolite

T - Reaction Temperature

TO4 - Tetrahedral unit where T= Al or Si

XRD - X-ray Diffraction technique

λ - Wavelength

2θ - Bragg Angle

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A Mass spectra of 2-phenyl-1-propanol 91

B Chromatograms of reactant (a) benzene (b) propylene

oxide (c) nitrobenzene as a solvent 92

C Nitrogen Adsorption Isotherm 94

D Calculation method of Conversion, Selectivity, Yield

and Percentage of Oligomerisation 96

CHAPTER 1

INTRODUCTION

1.1 General Introduction

The concept of catalysis was first discovered by Berzelius in 1836. The word

catalysis came from combination of two Greek words, κατα (kata) and λυδειν

(lysein) which was defined as ‘loosening down’ [1]. The phenomenon of catalysts

has been extensively studied since the early decades of the 19th century, and used

unconsciously for a much larger period. Nowadays, the catalyst market is seeing

moderate growth especially in fine chemicals and environmental markets sectors

which posesses higher perfoming. Meanwhile polymerization catalysts are growing

at more moderate rate, whereas refining and petrochemical catalysts are experiencing

low to flat growth. According to Comyns [2], the global catalyst market had a

volume of $10.5 billion in 2001 and is expected to grow to almost $13.5 billion or

4.6% per year by 2007. Environmental catalysts are the biggest segment in the

merchant, accounting for 27% of 2001 market. Polymerization catalysts are second

with nearly 22%, followed by refining (21%), petrochemical (20%) and fine

chemical and intermediates (10%). However, fine chemical and environmental

sectors are expected to grow at near or above 8% per year for the next 6 years. The

use of combinatorial catalyst for discovery and optimisation of catalytic performance

is expected to have a significant effect on the rate at which new catalysts are

2

developed [3, 4]. Basically catalyst can be classified into two types which are

homogeneous and heterogeneous catalyst. Homogeneous catalyst particularly Lewis

acid catalyst is well known and has been applied in Friedel-Crafts alkylation and

acylation reactions. However, new policies were introduced involving the

applications of homogeneous catalysts as a result of the problems caused by them;

such as corrosion, loss of catalyst and disrupting the environment [5]. The policies

focused on environment protection and avoidance of unfriendly reactants and

catalysts with better selectivity in order to minimize product waste and expensive

separations and recycling [6]. Meanwhile, heterogeneous catalysts such as molecular

sieves, zeolites and porous materials for liquid phase organic synthesis reactions can

give a lot of benefits such as clean reaction product solution after filtration, ease of

recovery and avoidance of corrosion. Therefore, development of efficient

heterogeneous catalysts is interesting and useful especially in the production of fine

chemical and intermediates.

1.2 Research Background

Recently, many perfume chemical and intermediates are produced on a large

scale by Friedel Crafts reactions. The reaction usually involves the alkylation or

acylation of an aromatic compound in the presence of Lewis acid catalyst. For

example, the Friedel Crafts alkylation of benzene with ethylene oxide is a

commercial route to produce β-phenethyl alcohol or 2-phenyl-ethanol. 2-phenyl-

ethanol is an important intermediate which is used because of its exquisite odour of

natural rose petal [7]. On the other hand, the alkylation of 2-methoxynapthalene with

propylene oxide is the preferred method to produce a precursor for non-steroidal,

anti-inflammatory agent naproxen [8, 9]. Basically, aluminium chloride is the most

common catalyst in the Friedel Crafts alkylation instead of sulphuric acid,

phosphoric acid, ferric chloride and boron trifluoride. The common alkylation agents

are olefin, alkyl halide, alcohol and epoxides [10].

3

The reaction of benzene or alkylbenzene with epoxides in the presence of

some homogeneous Lewis acid was first reported by Hata et al. [11]. Next, Nakajima

et al. [12] studied stereospecific Friedel-Crafts alkylation of benzene with propylene

oxide by aluminium chloride as Lewis acid catalyst and stereochemistry of ring

opening of epoxides. In 1970s, asymmetric induction in the Friedel-Crafts reaction of

benzene with (+)-1, 2-epoxybutane was studied by Nakajima et al. [13]. Meanwhile,

Inoue et al. [14] examined the reaction of toluene and anisole with 2-methoxyoxirane

and 2, 3-dimethyloxirane in the presence of aluminum chloride as Lewis acid. Later,

in the 80s, SnCl4 as catalyst on stereoselective Friedel-Crafts alkylation via epoxide

transannular and cycloalkylation reactions were studied [15, 16].

1.3 Problem Statement

Basically, introduction of hydroxyl group into an aromatic compound using

ethylene or propylene oxides are relatively well established in the presence of Lewis

acid catalysts. However, the selectivity of hydroxyalkylated products were affected

by side reactions such as epoxide oligomerisation or further reaction of the

hydroxyalkylated intermediate with the starting reactant to yield bisarylalkane

derivates.

Hence, a cleaner alternative process which is truly catalytic is needed due to

serious effluent problem associated with the use of a stoichiometric amount of AlCl3

and the corrosive reaction conditions. A lot of current processes in the production of

fine chemicals and intermediates are using homogeneous catalyst. The manufacture

of fine chemicals and intermediates involving the batch processes, are associated

with the production of large quantities of toxic waste [17]. Homogeneous catalysts

such as mineral acid, strong base and toxic metal reagent impose many drawback

including handling difficulties, inorganic contamination of organic products, the

formation of large volume of toxic waste and poor reaction selectivity leading to

unwanted isomers and side products [18].

4

In the hydroxyalkylation of aromatic with epoxides, the epoxides was added

into a suspension of anhydrous AlCl3 in the aromatic subtracts [19]. The postulated

mechanism of hydroxyalkylation proposed that aluminium chloride form an addition

compound with the epoxide which preferably opens at the most substituted carbon

atom [12]. As a result, a very reactive intermediate forms and reacts rapidly with the

aromatic and another molecule of epoxide. In this reaction, the tendency of epoxide

oligomerisation decreases due to dilution of epoxide [11]. The attack of the aromatic

gives rise to the formation of an alcohol-AlCl3 complex [20]. The complex is

generally soluble in the aromatic and is therefore more available than the unreacted

suspended AlCl3. The alcohol-AlCl3 complex becomes an increasingly important

negative factor since it is a polymerization catalyst for the epoxide [7]. Therefore, a

stoichiometric amount or excess of aluminium chloride and large excess of the

aromatic are needed to prevent oligomerisation of the epoxide. The complex has to

be decomposed with water in order to obtain the desired product. The reaction and

work-up also should occur below 25ºC; otherwise the alcohol-AlCl3 complex will

react further with another aromatic molecule to afford 1, 2-diaryalkanes [21].

Furthermore, AlCl3 catalyzed hydroxyalkylation requires a hydrolysis step resulting

in a hydrated AlCl3 waste stream. As a result, the catalyst is not reusable [14].

Extensive studies were conducted on alkylation and hydroxyalkylation of aromatic

using heterogeneous catalyst as a model reaction [22-26]. However, zeolites such as

H-ZSM-5, modernite, H-Beta and ZnNaY catalysed intermolecular

hydroxyalkylation of epoxides are very difficult because of competing epoxide

oligomerisation and rearrangement [21]. The main limitation of zeolites is the range

of pore sizes available. The small pore size of zeolites prevent it from being useful in

new applications with bulky and large molecule such as polymerization. Besides, the

cations present inside the structure may in some cases obstruct the pore apertures and

limit the rate of reactions [27]. In some cases for example, the formation of coke

which is deposited inside the pore of zeolite can hinder the normal diffusion of

reactants and products in and out of the catalyst [28, 29]. For this reason, in the past,

efforts were directed towards the synthesis of similar structures which led to the

discovery of MCM-41 [30]. Thus, the recent synthesis of mesoporous molecular

sieves MCM-41 has expanded the capabilities of heterogeneous catalyst. Compared

to zeolites, mesoporous MCM-41 materials is a useful candidate.

5

1.4 Research Objectives

The objectives of this research are:

1. To synthesize and characterize mesoporous Al-MCM-41 with different

SiO2:Al2O3 ratios through direct and secondary synthesis.

2. To study acidity properties of aluminium containing MCM-41.

3. To investigate the catalytic activity of hydroxyalkylation of benzene with

propylene oxide as a model reaction.

1.5 Scope of Study

In this research, Al-MCM-41 was synthesized by direct and secondary means

using sodium aluminate as the source of aluminium. Through both methods of

syntheses, aluminium was substituted for silicon in the framework and on the

surface. The insertion of aluminium into the framework of MCM-41 creates acid

sites. The structure and physical properties of catalyst were studied by X-ray

Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), 27Al and 29Si

Magic Angle Spinning Nuclear Magnetic Resonance, (27Al and 29Si MAS NMR),

Nitrogen Adsorption and Surface Area Analyzer. The acid properties of catalyst were

characterized using Temperature Programmed Desorption of Ammonia (TPD-NH3)

and Pyridine Adsorption Measurement. Al-MCM-41 was tested to catalyse the

hydroxyalkylation of benzene and propylene oxide; chosen as a model reaction, to

produce 2-phenyl-1-propanol. The testing of desired catalyst on the

hydroxyalkylation of ethylene oxide and benzene could not be carried out due to the

current strict regulation on the import of ethylene oxide. The Friedel-Crafts reactions

were carried out which include six main parameters, namely SiO2:Al2O3 ratios,

temperature, time on stream, reactant mole ratio composition, solvent and autoclave

reactor effect. The products will be characterized by Gas Chromatography and Mass

Spectroscopy techniques.

84

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