Supported group II transition metal catalysts in liquid phase reactions using borrowing hydrogen methodology 1

ACKNOWLEDGEMENT It has been a truly memorable learning journey in completing the research work and I would like to take this opportunity to acknowledge those who have been helping and supporting me along the way. First of all, I would like to express my gratitude to my supervisor, Associate Professor Dr. Stephan Jaenicke for giving me the opportunity to work on the project in the research lab. I truly appreciate his help, stimulating suggestions and encouragement throughout the project. I specially thank Associate Professor Dr. Chuah Gaik Khuan for her untiring help and invaluable advice throughout the time of research and writing of this thesis. The support by Madam Toh of the Applied Chemistry lab and all the other members of the technical staff at NUS was indispensable for the success of my work. I am very grateful for their help. I also acknowledge Miss Nie Yuntong, Mr. Do Dong Minh, Mr. Fan Ao, Mr. Wang Jie, Miss Gao Yanxiu, Miss Toy Xiu Yi, Miss Han Aijuan, Mr Goh Sook Jun, Mr Sun Jiulong and all the members of our research group, for their kind help and encouragement during my candidature. Especially, I would like to give my special thanks to my husband for believing in me and giving me the inspiration and moral support when it was most required. I am also grateful to my parents, for their unconditional love, encouragement and motivation. Lastly, I am indebted to the National University of Singapore for providing me with a valuable research scholarship and for funding the project. i TABLE OF CONTENTS PAGE Acknowledgement i Table of Contents ii Summary vi List of publications viii List of Tables ix List of Schemes xi List of Figures xiii CHAPTER 1.1 Introduction Supported group 11 nanosized transition metal catalysts in fine chemical synthesis 1.2 1.3 1.1.1 Synthesis of supported group 11 catalysts 1.1.2 Group 11 based catalysts in liquid phase reactions Borrowing Hydrogen methodology in fine chemical synthesis 1.2.1 Activation of alkanes 1.2.2 Activation of alcohols 1.2.3 Activation of amines Aims and outline of this thesis 21 36 References ii CHAPTER Catalyst Characterization Techniques 2.1 Nitrogen Porosimetry 46 2.2 XRD 50 2.3 TEM 53 2.4 X-ray photoelectron Spectroscopy 55 2.5 Temperature Programmed Desorption 58 2.6 Inductively Coupled Plasma Atomic Emission Spectroscopy 59 2.7 CO-adsorption IR 61 References CHAPTER Oxidation of alcohols over supported Ag catalysts 3.1 Introduction 64 3.2 Experimental and Catalytic Testing 67 3.3 Results & Discussion 68 3.4 Conclusion 95 References CHAPTER Alumina-entrapped Ag catalysts for N-alkylation of amines with alcohols via borrowing hydrogen methodology 4.1 Introduction 101 4.2 Experimental and Catalytic Testing 104 4.3 Results & Discussion 106 4.4 Conclusion 125 References iii CHAPTER Alumina-entrapped Ag catalysts for reductive amination of alcohols using nitroarenes via borrowing hydrogen methodology 5.1 Introduction 130 5.2 Experimental and Catalytic Testing 132 5.3 Results & Discussion 133 5.4 Conclusion 146 References CHAPTER Self-coupling of benzylamines over highly active and selective alumina-entrapped Cu catalysts to produce secondary benzylamines using borrowing hydrogen methodology 6.1 Introduction 150 6.2 Experimental and Catalytic Testing 154 6.3 Results & Discussion 155 6.4 Conclusion 171 References CHAPTER Magnesia supported Ni catalysts modified with silver for the selective hydrogenation of benzonitrile 7.1 Introduction 174 7.2 Experimental and Catalytic Testing 178 7.3 Results & Discussion 179 7.4 Conclusion 197 iv References CHAPTER 8.1 Conclusions Conclusion 201 v Summary The borrowing hydrogen methodology is an interesting protocol for the activation of alcohols and amines towards nucleophilic substitution reactions. The reaction sequence usually starts with the abstraction of a hydrogen molecule from the starting reagent R1-XH (X = O, NH,…) by a catalyst. This generates an unsaturated species R1=X which can condense with R2 to form an unsaturated intermediate. The abstracted hydrogen is then returned and hydrogenates this intermediate to generate the final product. It is a very “green” and highly atom efficient protocol for C-C and C-N bond formation with very little byproducts and waste production. This methodology had been developed with homogeneous catalysts for reactions such as N-alkylation, indirect Wittig reactions, and C-C bond formation reactions. Heterogeneous catalysts have many advantages over homogenous ones such as easy separation and recovery. The aim of this thesis was to investigate suitable heterogeneous catalysts for liquid phase reactions using the hydrogen borrowing methodology. Heterogeneous group 11 transition metals (Au, Ag and Cu) had been shown to be active in many liquid phase reactions like catalytic oxidation, catalytic hydrogenation and catalytic C-C coupling. We developed a heterogeneous silver catalyst which is very active for the oxidative dehydrogenation of alcohols, with good selectivity to the corresponding aldehyde or ketone. This hydride removal is the crucial step in the activation of alcohols for subsequent coupling with suitable nucleophiles. In the course of this Thesis, catalysts were prepared based on well dispersed supported group 11 metals (Ag and Cu), and their activities were tested in a number of catalytic reactions including the N-alkylation of amines by alcohols, reductive vi N-alkylation of nitroarenes by alcohols, and self-coupling of aromatic amines, in all cases using the borrowing hydrogen methodology. In these reactions, the group 11 metal was the active species. We also investigated a hydrogenation reaction, where Ag by itself was essentially inactive. However, when Ag was incorporated in a formulation with nickel, it was found to be able to greatly enhance the selectivity in the catalytic hydrogenation of benzonitrile to benzylamine. vii LIST OF PUBLICATIONS (1) Journal papers 1. H. H. Liu, G. K. Chuah, S. Jaenicke*, N-alkylation of amines by alcohols over alumina-entrapped Ag catalysts using “borrowing hydrogen” methodology, J. Catal 292.(2012) 130 (2) Conference papers 1. Aerobic Alcohol Oxidation by supported Ag catalysts H. H. Liu, G. K. Chuah, S. Jaenicke* (Poster at the 6th Asian-European Symposium on Metal Mediated Efficient Reactions, June 7-9, 2010, Singapore) 2. Investigation of hydrogen produced from the dehydrogenative oxidation of alcohols over Ag catalysts H. H. Liu, G. K. Chuah, S. Jaenicke* (Poster at the 3rd Singapore Catalysis Forum, May 17, 2010, Singapore). 3. Selective hydrogenation of nitriles to primary amines over hetergeneous Nickel-silver catalyst in liquid phase H. H. Liu, G. K. Chuah, S. Jaenicke*, (Poster at the 14th Asian Chemical Conference (ACC), Sep 5-8, 2011, Bangkok, Thailand) 4. Role of oxygen in dehydrogenation of alcohols over Ag/Al2O3 H. H. Liu, S. Jaenicke, G. K. Chuah*, (Poster at the 6th Asia-Pacific Congress on Catalysis (APCAT), Oct 13-17, 2013, Taipei, Taiwan) 5. Reduction amination of Reductive N-alkylation of nitro compounds with alcohols over entrapped Ag catalysts H. H. Liu, G. K. Chuah, S. Jaenicke, *, (Poster at the 6th Asia-Pacific Congress on Catalysis (APCAT), Oct 13-17, 2013, Taipei, Taiwan) viii LIST OF TABLES Table 1-1 Basic physical properties of group 11 transition metals Table 1-2 Isoelectric point (IEP) of commonly used inorganic supports Table 1-3 Examples of group 11 metal catalysed oxidation reactions Table 1-4 Examples of supported group 11 metal catalysed hydrogenation reactions Table 2-1 Parameters of XPS measurements Table 3-1 Textural properties of screened supported Ag catalysts in the benzyl alcohol oxidation Table 3-2 Effect of hydrogen pre-treatment time at 300 °C on Ag crystallite size for 10 wt. % Ag/Al2O3 Table 3-3 XPS results for calcined and H2-treated 10 wt. % Ag/Al2 O3 Table 3-4 Catalytic dehydrogenation of benzyl alcohol to benzaldehyde under oxygen flow Table 3-5 Oxidation of various primary and secondary alcohols catalysed by 10 wt. % Ag/γ-Al2O3 Table 3-6 Effect of catalyst pre-treatment on hydrogen formation during benzyl alcohol oxidation in the open system Table 3-7 Conversion of benzyl alcohol and H2 detection under different reaction conditions and catalyst pre-treatments Table 4-1 Textural properties of the catalysts in the N-alkylation of benzyl alcohols with anilines Table 4-2 N-alkylation of aniline with benzyl alcohol over various catalysts Table 4-3 Correlation between the size of nanocluster and Ns in the reaction mixture Table 4-4 Scope of Ag catalyst on the N-Alkylation of amines with alcohols Table 4-5 Reaction studies and conditions in the N-alkylation of benzyl alcohols with anilines ix Table 5-1 N-alkylation of nitroarenes using alcohols Table 5-2 Effect of the ratio benzyl alcohol/nitrobenzene on the yields after 19 h Table 5-3 Results of the reductive alkylation of nitroarenes with alcohols Table 5-4 Reaction studies and conditions in the N-alkylation of nitroarenes using alcohols Table 6-1 Textural properties of the catalysts in the self-coupling of benzyl amines tested Table 6-2 Self-coupling of benzyl amine in the presence of different catalysts. Table 6-3 Self coupling of various amines Table 6-4 Reaction studies and conditions in the self-coupling of benzylamines Table 7-1 Chemical and textural properties of the catalysts used in benzonitrile hydrogenation Table 7-2 Total basicity of NixAgy/MgO catalysts Table 7-3 XPS Binding energies for Ni-Ag catalysts on MgO supports Table 7-4 Summary of the activities of catalysts in the benzonitrile hydrogenation x Table 7-4. Summary of the activities of catalysts tested N NixAgy/MOz EtOH, H2 10 bar, 100 oC BN NH2 BA Entry Catalyst NH N DBA DBI T (h) Conv. (%) Selv. (BA) (%) No catalyst 20 -- -- MgO 20 -- -- Ag20/MgO 20 20 Ni20/MgO 85 60 Ni10Ag10/TiO2 >99 74 Ni10Ag10/SiO2 98 72 10 Ni10Ag10/ZnO 98 91 11 Ni10Ag10/Al2O3 >99 75 12 Ni10Ag10/MgO >99 98 13 Ni10Ag10/MgOa -- -- 14 Ni10Ag10/MgOb 98 97 15 Ni10Ag10/MgOc >99 97 Reaction Condition: BN mmol, catalyst: 100 mg, ethanol (solvent) 10 ml Autoclave, temp 100 o, PH2 = 10 bar, a : without H2 activation b: second reuse c: third reuse It was necessary to activate the catalyst prior to use. Results from all the catalytic runs are summarized in Table 7-4. Silver on MgO shows no activity at all, and even at 20 wt. %, was nearly inactive for the formation of benzylamine. Metallic nickel was determined to be the major hydrogenation metal. However, the selectivity 189 towards benzyl amine over nickel on MgO was quite low, with 30 % towards DBI/DBA. Complete conversion of benzonitrile and a good yield of benzylamine can be achieved when Ag was added to Ni/MgO (Ni10Ag10/MgO, Figure 7-6). To optimize the composition in the bimetallic system NixAgy/MgO, catalysts with different ratio of Ag/Ni were prepared and tested under the standard reaction conditions described previously. The optimal mass ratio of the two metals was determined to be Ni: Ag 10: 10, which corresponds to a molar ratio of 1.8:1. The side reaction leading to higher amines was catalysed by the acid sites of the support or by the metallic Ni sites. It MgO generally accepted to be a basic support; acidic sites at the support probably not play a major role with this catalyst. The beneficial effect of Ag addition is explained as follows. Incorporation of Ag into Ni breaks up the large continuous Ni ensemble and suppresses the side reaction. On the other hand, the modification of the acid-base properties of the MgO support (see TPD-CO2 results) by the silver addition allows to retain the basic properties of MgO and thereby reduces the occurrence of side reactions. 190 130 100 95 90 85 90 80 70 75 Selv.(%) Conv.(%) 110 70 50 65 30 0% 20% 40% 60% 80% 60 100% Ag/Ag+Ni weight % Figure 7-6. Effect of composition on the activity for the benzonitrile hydrogenation Reaction condition: BN mmol, catalyst: 100 mg, ethanol: 10 ml, temp 100 oC, PH2 = 10 bar, h The result on the optimization of the react condition is illustrated in Figure 7-7(a) and Figure 7-7(b). The influence of hydrogen pressure on the conversion of BN and the selectivity to BA in ethanol over 20 wt. % Ni10Ag10/MgO catalyst is shown in Figure 7-7(a). It is apparent that high conversion and selectivity to BA (98 %) were achieved above 10 bar H2. At the lower pressure of bars, the yield and selectivity were slightly reduced. However, the decrease became quite substantial when the pressure was further reduced. At bar H2 (~ 4.1 mmol H2), the conversion was only 15 % and the selectivity was reduced to 40 %. This is probably partially caused by insufficient H2 supply, rather than being a genuine pressure effect. Nevertheless, using a set up with automatic H2 dosing at constant pressure at bar, only a moderate conversion of 58 % was obtained after h. The H2 uptake during the benzonitrile hydrogenation at bar H2 in large scale (8 mmol substrate) was monitored (Figure 7-7b) and 9.7 mmol H2 was consumed during the benzonitrile hydrogenation, which corresponds to 60 % benzonitrile conversion (Scheme 7-2). This fits quite well with the results obtained from the GC analysis. 191 CH2NH2 CN + 2H2 CN + Scheme 7-2. 2H2 N H Stoichiometric equation of benzonitrile hydrogenation The influence of temperature on the conversion of BN and the selectivity to BA over the 20 wt. % Ni10 Ag10/MgO catalyst is given in Figure 7-7 (c). As seen, the highest conversion and selectivity to BA (98 %) were achieved above 90 oC while a dramatic decrease of the activity was seen when the temperature drops below 90 oC. 192 (a)100 80 Sel.(%) 80 60 60 40 40 Conv. (%) 100 20 20 0 10 15 20 Pressure (bar) H2 uptake (mmol) (b) 12 10 0 100 200 300 time (min) 100 100 98 Conv.(%) 80 60 96 40 94 20 92 Sel.(%) (c) 90 40 60 80 100 120 Temperature (oC) Figure 7-7. Effect of pressure and temperature on the activities of the benzonitrile hydrogenation Reaction Condition: (a) BN mmol, catalyst: 100 mg, ethanol: 10 ml, temp 100 oC, h (b) BN: mmol, ethanol : 40 ml, catalyst: 400 mg, PH2 = bar, temp 100 oC, h (c) BN: mmol, catalyst: 100 mg, ethanol :10 ml, PH2 = 10 bar, h 193 As with the other reactions, a leaching test was done to confirm that the reaction is indeed heterogeneously catalysed (Figure 7-8). After h, the reaction was stopped and the catalyst was removed from the reaction mixture by centrifugation. The clear supernatant was again brought to reaction conditions, but over the next hours, no further reaction was observed. 100 Conv.(%) 80 60 40 Conv.(%) 20 leaching test 0 Time (h) Figure 7-8. Hydrogenation of benzonitrile with and without Ni10 Ag10/MgO (catalyst was removed by filtration after h). The activity of Ni10Ag10/MgO was tested for reuse. After the reaction in the autoclave, the catalyst was recovered by filtration, washed with acetone and reactivated in H2 at 300 °C. The rate of reaction was very similar to the fresh catalyst and the primary amine was formed with yields of 95 – 98 %. According to the model proposed by von Braun [23], the hydrogenation of benzonitrile proceeds via phenylmethanimine. Secondary amines are formed by desorption of the imine-intermediate from the catalyst surface, which subsequently reacts in solution with benzylamine. Elimination of ammonia yields N-benzylidene-1 –phenylmethanamine (DBI) as condensation product. Subsequent hydrogenation provides dibenzylamine (DBA). The postulated intermediate phenylmethanimine was not found in the reaction mixture. However, the transient concentration of 194 phenylmethanimine will be very low if it is consumed as fast as it is formed. Closer inspection of the time-yields diagram (Figure 7-9) shows that the condensation products of phenylmethanimine and benzylamine, DBI and DBA, were the only byproducts. The byproducts formation was somehow inhibited during the early phase of the reaction. This suggests that phenylmethanimine or other intermediates taking part in the first step of byproduct formation did not desorb into the liquid phase. Thus, the side product DBI most likely results from a bimolecular condensation reaction occurring on the catalyst surface. According to the model suggested by Krupka [5] on the Ni, Pd and Pt catalysed nitrile hydrogenations; the mechanism is proposed and shown in Scheme 7-3. Carbenes and nitrenes can be formed as surface intermediates, with nitrenes being the preferred species for metallic nickel [5]. In the initial step of the condensation reaction, a nitrogen nucleophile attacks an unsaturated carbon atom, such as the carbon atom of a carbene. This step of the condensation process, catalysed on Lewis acid sites, is somehow inhibited in the basic support MgO. Also, the smaller nickel ensemble size reduces the chance of adsorption of benzylamine and phenylmethanimine or the bimolecular intermediate, i.e. higher imine, at the neighbouring site. The side reaction (pathway in Scheme 7-3) to higher amine is therefore disfavoured on the basic MgO supported Ni modified by Ag catalyst. The catalyst Ni10 Ag10/MgO was found to be a good heterogeneous catalyst for the hydrogenation of benzonitrile, and high selectivity (>98 %) towards primary amine was maintained up to very high conversion, without need for NH3 addition. 195 Conv./Sel.(%) 100 80 Conv.(%) BA (%) DBA (%) DBI 60 40 20 0 Time (h) Figure 7-9. Reaction profile for the N-alkylation of aniline by benzyl alcohol in the presence of Ni10Ag10/MgO. Reaction conditions: BN mmol, catalyst: 100 mg, ethanol: 10 ml, temp 100 oC, PH2 = 10 bar, h, reaction was stopped at h, h , h , h and h. Nitrene NH2 X CH2 N pathway + condensation M Ni CH2 NH2 +H2 BA +H2 M Ni +H2 C C N NH2 NH2 H2N M Ni pathway C NH2 condensation M Amino-carbene Ni HC NH NH2 Ni -NH3 H2C NH HC +H2 N NH C DBA M Ni M M Ni Ni DBI Scheme 7-3. Suggested surface reaction mechanism for the catalytic hydrogenation of benzonitrile 196 7.4 Conclusions In the hydrogenation of benzonitrile to benzylamine, the formation of condensed by-products occurs by a transamination reaction. These undesired reactions take place on both the metal and acid sites. The addition of Ag to the Ni/MgO catalysts, prepared by the co-impregnation method, influences the acid/base character of the support surface and the surface properties of Ni sites. The TPD-CO2 provides evidence that the Ni10 Ag10/MgO catalyst has both weak and strong basic sites. 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Chem. 32 (1940) 1193. 200 Chapter Conclusion The results of the present studies deal with the application of group 11 metals (mainly silver and copper) based catalysts on the liquid phase organic reactions using borrowing hydrogen methodology. The thesis highlights the importance of the instinct properties of metals, crystallite size, specific surface area, the porous structure, and the effect of pre-treatment conditions on the activities of the catalysts. The starting point of this whole thesis is to find out whether the energy unflavoured reaction of dehydrogenation of alcohols to produce gaseous H2 under oxygen free conditions possible or not. Alumina-supported silver catalysts were synthesized and showed good activity for the oxidation of aromatic alcohols to their corresponding carbonyls in open systems with no active influx of oxygen. The pre-treatment conditions of hydrogen treatment of the calcined Ag/Al2O3 catalyst resulted in a redispersion of silver into smaller particles and the surface of the supported catalyst became enriched in silver. Two parallel pathways are involved in the oxidation of benzyl alcohol to benzaldehyde, one involving surface oxygen to form water and the other, an anaerobic route where gaseous H2 was formed. From studies in closed systems, it was confirmed that the dehydrogenation route amounted to less than 2.5 % of the total transformation and is always coupled to the oxidative reaction leading to H2O formation. In the absence of oxygen, such as in flowing nitrogen, the dehydrogenation of the alcohol was therefore not observed. The presence of chemisorbed oxygen on the reduced silver surface was postulated to be the active species for the oxidation reaction. Since the dehydrogenation of alcohols to aldehydes could be achieved in controlled conditions with silver catalyst, it will be worthwhile 201 to test whether the liberated H2 can be returned as the borrowed H2 to the system. After the liberation of H2 was found to be possible in the alcohol oxidation, silver-based catalysts with smaller silver crystallite size were prepared. The catalysts were prepared by adding a silver precursor to an Al alkoxide solution, and allowing the system to undergo polymerization under conditions of sol-gel processing. The resulting solid was calcined at 600 °C and the synthesized Ag/Al2O3 samples were active for the N-alkylation of amines with alcohols. A loading of 2.4 wt. % Ag was found to be optimal. The higher activity compared to samples prepared by wet impregnation shows that the intimate mixing of silver and the support is important. The addition of Cs2CO3 or K3PO4 as a base promoter improved the activity and selectivity to amines. N-Benzylaniline was formed in > 99 % yield from aniline and benzyl alcohol. The base promoter is necessary for the efficient dehydrogenation of the alcohol to the corresponding carbonyl compound which reacts selectively with the primary or secondary amine to form the imine. Hydrogenation of the imine to the desired amine takes place under an inert atmosphere using the self-generated hydrogen from alcohol dehydrogenation. In addition to the tertiary amines, amides were formed when piperidine and pyrrolidine were reacted with benzyl alcohols. This type of heterogeneous Ag/Al2O3 can be recycled and reused without loss of activity and selectivity. The scope of the silver based catalysts were explored and the catalysts were found to be active in the direct reductive mono N-alkylation of a range of aromatic nitro compounds with alcohols similarly via a hydrogen-borrowing strategy. Alcohols serve two roles in the multi-step process, one as the alkylation agent and the other as the hydrogen source for nitro group reduction. This process has significant advantages when compared with other N-alkylation methods, such as cheap and readily available 202 reactants, high catalytic activity and selectivity, and lastly no external molecular hydrogen or other stoichiometric reducing agents necessary in our catalytic system. The reaction is a multi-step process catalysed by the same catalyst system. After exploring the possibility of alcohols acting as the electrophiles, the activities of amines as the electrophiles were tested. Al2O3-supported copper catalysts were found to be an effective heterogeneous catalyst for the self-coupling of amines, including aromatic and linear amines. The copper-based catalysts were generated by in-situ precipitation of a copper precursor together with an aluminium oxyhydroxide support, followed by calcination at 600 °C. The reaction proceeds through the hydrogen-borrowing mechanism. Yield of > 90 % of dibenzylamine can be obtained from the self-coupling of benzylamine in 24 hours in the external hydrogen free condition. Ag catalysts did not perform well in this reaction, because they did not catalyse the dehydrogenation of the amine very well. Reduction of the copper catalyst in a pre-treatment step was important, indicating that the metal, but not the oxide is the active species. Lastly, the activity of silver acting as a co-catalyst was explored in chapter 7. Since group 11 metals could act as a catalyst in the oxidation reaction, the activity of this type of catalyst in the reduction reaction was explored. The test reaction is the hydrogenation of benzonitrile to benzylamines. However silver catalyst showed no activity in the hydrogenation of benzonitriles to benzylamines using gaseous H2 under the described conditions. Nickel was found to be good candidate for the reaction but it had low selectivity to the target product, which is the primary amine. The formation of condensed by-products occurs by a transamination reaction and these undesired reactions catalysed by acid take place on continuous metal site. The TPD-CO2 provides evidence that the Ni10Ag10/MgO catalyst has both weak and strong basic 203 sites and the breakup of a large continuous nickel ensemble by silver addition affects the adsorption of the intermediate. After properly activating the catalyst by reduction in flowing hydrogen at 300 oC, Ni10Ag10/MgO exhibits high activity, and complete conversion of the substrate with a very high selectivity to primary amine (>98 %) in a liquid ammonia free system. The main factors determining the selectivity to primary amine in this hydrogenation were found to be the Ni to Ag ratio, temperature and pressure. Relatively mild reaction conditions (100 oC, 10 bars) are sufficient to obtain the primary amines in high yield. 204 [...]... reacting with other molecules on the surface The transition metals most frequently used in catalysts belong to the groups 8 to 11 , and particularly the group 11 transition metals Au, Ag and Cu are receiving more and more attention due to their increasing applications in catalysis 1. 1 .1 Synthesis of supported group 11 catalysts The Group 11 of the periodic table, also called the copper group or in the... alloying with other metals, making it a source for reliable tools and weapons 4 Table 1- 1 Basic Physical Properties of Group 11 transition metals Cu Ag Au Atomic Weight 63.5 10 7.9 19 7.0 Electron configuration [Ar]3d104s1 [Kr]4d105s1 [Xe]4f145d106s1 Crystal structure f c c.a f c c a f c c a Metallic radius (Å) 1. 28 1. 44 1. 46 Density (g/cm3) 8.96 10 .5 19 .3 10 85 962 10 64 Electronegativity (Pauling) 1. 90 1. 93... for each individual supported metal precatalyst 1. 1.2 Group 11 based catalysts in liquid phase reactions The application of copper -group based heterogeneous catalysts in fine chemicals synthesis can be generally divided into: catalytic oxidation, catalytic hydrogenation and catalytic C-C bond formation The following sections give an overview of 11 reactions catalysed by group 11 metals 1. 1.2 .1 Oxidation... Scheme 1- 1 Proposed mechanism of nitroaromatic hydrogenation over an Ag nanocluster Scheme 1- 2 Metal catalysed cross coupling Scheme 1- 3 Borrowing hydrogen scheme in fine chemical synthesis Scheme 1- 4 Activation of alkane by borrowing hydrogen Scheme 1- 5 Activation of alcohol by borrowing hydrogen Scheme 1- 6 Types of reactions applied by the activation of alcohols using borrowing hydrogen Scheme 1- 7 General... catalyst surface Various metals and metal oxides including group 11 transition metals have been applied in oxidation reactions [ 21] Table 1- 3 lists several oxidation reactions that have been catalysed by group 11 metals 12 Table 1- 3 Examples of oxidation reactions catalysed by Group 11 metals metal Examples of oxidation reactions Catalyst used reference Au CO oxidation to CO2 Au/TiO2 [10 8] cyclohexane oxidation... air-calcined (ii) H2-treated 10 wt % Ag/Al2 O3 catalysts for 15 min (iii) H2-treated 10 wt % Ag/Al2O3 catalysts for 30 min (iv) H2-treated 10 wt % Ag/Al2O3 catalysts for 60 min (v) H2-treated 10 wt % Ag/Al2O3 catalysts for 12 0 min xiv Figure 3 -10 Determination of rate constant by plotting –ln (1- C) versus time (a) treduction = 0 min (b) treduction = 5 min (c) treduction = 15 min (d) treduction = 30 min (e)... Au/ZSM [10 9] cyclohexanol and cyclohexanone Au/SBA -15 [11 0], [11 1] propylene epoxidation to alcohols Au/SiO2 [11 2] Au/Ti-HMM [11 3] Au/TS -1 [11 4] Au/TiO2 [11 5] aldehyde oxidation to acids and Au/ hydrotalcite [20] esters Au/TiO2 [11 6] Au/C [11 7] PO oxidation to carbonyls Au/CeO2 Ag/SiO2 [11 8] Ag/α- Al2O3 [11 9] Alcohol oxidation to carbonyls Ag/hydrotalcite [12 0] Ag/γ-Al2O3 [7] Ag/SiO2 [30] Ag/CaO [12 1] CO... silver were re-investigated as catalysts for hydrogenation reactions It turned out that they were indeed promising for several selective hydrogenation reactions like the hydrogenation of unsaturated carbonyls to unsaturated alcohols, and of nitro compounds to amines (Table 1- 4) 15 Table 1- 4 Hydrogenation reactions catalysed by supported group 11 metals metals Reactions Catalysts Ref Au Alkynes hydrogenation... Ni2Ag18/MgO (ii) Ni4 Ag16/MgO (iii) Ni10 Ag10/MgO (iv) Ni15Ag5/MgO (v) Ni20/MgO (vi) MgO (a) N2 isotherm (b) pore size distribution Figure 7-3 (a) XRD patterns of (i) Ni2 Ag18/MgO (ii) Ni4 Ag16/MgO (iii) Ni10Ag10/MgO (iv) Ni15 Ag5/MgO (v) Ni20/MgO (b) TEM images of Ni10 Ag10/MgO(Avg alloy size ~ 7 nm) (c) size distribution obtained from Fig 7-2(b) Figure 7-4 CO2 TPD spectra of (i) MgO (ii) Ni2 Ag18/MgO... Ni10Ag10/MgO (catalyst was removed by filtration after 1 h) Figure 7-9 Reaction profile for the N-alkylation of aniline by benzyl alcohol in the presence of Ni10 Ag10/MgO Reaction conditions: BN 2 mmol, catalyst: 10 0 mg, ethanol: 10 ml, temp 10 0 oC, PH2 = 10 bar, 5 h, reaction was stopped at 1 h, 2 h , 3 h , 4 h and 5 h xvii Chapter 1 General Introduction 1. 1 Supported nanosized transition metal catalysts . catalysts in fine chemical synthesis 1 1. 1 .1 Synthesis of supported group 11 catalysts 1. 1.2 Group 11 based catalysts in liquid phase reactions 1. 2 Borrowing Hydrogen methodology in fine chemical. ii Summary vi List of publications viii List of Tables ix List of Schemes xi List of Figures xiii CHAPTER 1 Introduction 1. 1 Supported group 11 nanosized transition metal catalysts in. of this thesis was to investigate suitable heterogeneous catalysts for liquid phase reactions using the hydrogen borrowing methodology. Heterogeneous group 11 transition metals (Au, Ag and Cu)