Materials for solid base catalysts and oxygen storage

MATERIALS FOR SOLID BASE CATALYSTS AND OXYGEN STORAGE VADIVUKARASI RAJU NATIONAL UNIVERSITY OF SINGAPORE 2009 Acknowledgement First of all, I would like to express my gratitude to my supervisor, Associate Professor, G.K. Chuah, for giving me the opportunity to work in her laboratory. Without her guidance, stimulating suggestions, patience and encouragement this research work would not have been possible. I would also like to thank Associate Professor, S. Jaenicke for his invaluable advice and help. Appreciation also goes to my labmates particularly, Zhou weihua, Fow Kamloon, Nie Yuntong, Do Minh, Rajitha Radhakrishnan, Zhong Liang, Jeck Fei for their help and encouragement. I would also like to thank my parents, brother and my husband for their constant support, understanding and encouragement. Lastly, I am indebted to the National University of Singapore for providing me with a research scholarship. i Table of contents Pg. No Acknowledgement i Table of contents ii Summary vii List of publications x List of tables xii List of schemes xiv List of figures xv Chapter Introduction 1.1 General Introduction 1.2 Solid base catalysts 1.3 Types of solid base catalysts 1.3.1 Metal oxides 1.3.2 Supported catalysts 1.3.3 Basic zeolites 1.3.4 Mesoporous materials 1.3.5 Layered clay materials 1.4 Applications of solid base catalyst for organic reactions 10 1.4.1 Epoxidation reaction 10 1.4.2 Knoevenagel reaction 11 1.4.3 Aldol condensation 12 1.5 Three way catalyst 14 1.5.1 Background-OSC 15 1.5.2 Role of CeO2 in TWCs 16 1.5.3 Deactivation of oxygen storage capacity 17 1.5.4 Ceria based systems 17 1.6 Aims of the present study 18 References 23 ii Chapter Experimental 2.1 Catalyst characterization techniques 28 2.1.1 X-Ray powder diffraction 28 2.1.2 BET surface area and porosity measurement 29 2.1.3 Temperature programmed desorption 31 2.1.4 Induction coupled plasma-Atomic emission spectroscopy (ICP-AES) 34 2.1.5 X-Ray photoelectron spectroscopy 34 2.1.6 Electron microscopy 36 References 38 Chapter Epoxidation of olefins by supported cesium and lanthanum oxides using aqueous hydrogen peroxide as oxidant 3.1 Introduction 39 3.2 Experimental 43 3.2.1 Preparation of supported cesium/lanthanum oxide catalysts 43 3.2.2 Epoxidation of olefins 44 3.3 Catalyst characterization 45 3.3.1 X-ray diffraction 45 3.3.2 Nitrogen adsorption desorption 45 3.3.3 CO2-Temperature programmed desorption 46 3.4 Catalytic testing 47 3.4.1 Effect of surfactants 48 3.4.2 Influence of H2O2/Olefin ratio 49 3.4.3 Effect of solvents 50 3.4.4 Epoxidation using various supported catalysts 50 3.4.5 Effect of Al2O3 51 3.4.6 Epoxidation of various olefins using 10-Cs-SBA-15 catalyst 52 3.4.7 Stability and reusability of the catalyst 53 3.5 Discussion 53 3.6 Conclusion 55 References 71 iii Chapter Nanocrystalline supported MgAl-HTs on SBA-15 as highly active solid base catalyst 4.1 Introduction 74 4.2 Experimental 78 4.2.1 Preparation of the support SBA-15 78 4.2.2 Preparation of supported hydrotalcite catalyst 79 4.2.3 Knoevenagel condensation 81 4.3 Catalyst characterization 81 4.3.1 X-Ray powder diffraction 81 4.3.2 BET surface area analysis 83 4.3.3 TPD measurements 84 4.3.4 Transmission electron microscopy 85 4.4 Catalytic testing 85 4.4.1 Catalysts prepared by different methods 86 4.4.2 Catalysts preparation at different pH 88 4.4.3 Influence of loading of HT on the support 88 4.4.4 Recycling of the catalyst 89 4.5 Discussion 90 4.6 Conclusions 91 References 108 Chapter Synthesis of pseudoionone by KF/alumina 5.1 Introduction 111 5.2 Experimental 115 5.2.1 Preparation of supported KF catalyst 115 5.2.2 Aldol condensation reactions 116 5.3 Pseudoionone synthesis using commercial Fluka KF/alumina 116 5.3.1 Influence of temperature 117 5.3.2 Influence of acetone/citral mole ratio 118 5.3.3 Influence of catalyst amount 119 5.4 Pseudoionone synthesis using KF/alumina prepared by wet impregnation 119 5.4.1 Effect of KF loading and pretreatment temperature of catalyst 120 iv 5.4.2 Effect of reaction temperature 121 5.5 Discussion 122 5.6 Conclusions 123 References 138 Chapter Correlation between basicity and the activity for various base catalysts 6.1 Introduction 140 6.2 Basicity measurement 140 6.3 Result and discussion 141 6.3.1 Supported cesium lanthanum oxides 141 6.3.2 Supported hydrotalcites 142 6.3.3 Supported KF on alumina 144 6.4 Conclusion 146 References 151 Chapter Effect of hydrothermal treatment and silica and iron doping on the thermal stability and oxygen storage capacity of ceria-zirconia 7.1 Introduction 153 7.2 Experimental 157 7.2.1 Preparation of ceria-zirconia 157 7.2.2 Preparation of silica and iron oxide doped ceria-zirconia 157 7.3 Catalyst characterization 158 7.3.1 X-Ray powder diffraction 158 7.3.2 BET surface area analysis 160 7.3.3 X-Ray photoelectron spectroscopy 163 7.3.4 Transmission electron microscopy 164 7.3.5 Isopropanol dehydration 165 7.4 Oxygen storage capacity 166 7.4.1 Effect of ceria zirconia mole ratio 166 7.4.2 Influence of hydrothermal treatment on the oxygen storage capacity 167 v 7.4.3 Influence of different wt% of silica doping on OSC 168 7.4.4 Effect of hydrothermal treatment on silica-containing ceria-zirconia 168 7.4.5 Influence of different wt% of iron-doping on OSC 169 7.4.6 Effect of hydrothermal treatment on iron-doped ceria-zirconia 170 7.4.7 Effect of high temperature treatment on the surface area and OSC 171 7.5 Discussion 172 7.6 Conclusions 175 References 214 vi Summary This thesis investigates oxides as solid base catalysts and as oxygen storage material. Solid base catalysts are widely used for the synthesis of fine chemicals because of their environmentally benign nature and the possibility to prepare different types of active sites (Brønsted and Lewis sites) with a range of basic strength. Understanding the nature of active sites present and correlation of the structureactivity relationship helps in better understanding of the catalytic activity. Supported cesium and lanthanum oxides on SBA-15 were prepared using the wet-impregnation method and tested for the epoxidation of olefins using H2O2 as oxidant, after calcination at 500 °C. The supported cesium oxide catalysts were more active than the lanthanum oxide samples. With 10 wt% loading of cesium on SBA-15, 97% conversion can be achieved after h with a high selectivity of 90% to cyclohexene oxide. The use of surfactant, dodecyltrimethylammonium bromide, was important for a high conversion as the reaction mixture was bi-phasic, comprising of organic olefin and the aqueous H2O2. The surface area of the supported cesium oxides was lower than that of the lanthanum oxides. By forming a mixed cesium-lanthanum oxide phase on the support, a high surface area was obtained. However, the catalytic activity was decreased. Besides cesium and lanthanum oxides, Mg-Al hydrotalcite was also supported onto siliceous SBA-15 and MCM-41 to obtain high surface areas up to 700 m2/g and to allow better dispersion of the basic sites. These samples were active in the Knoevenagel condensation reaction between benzaldehyde and ethylacetocyanate and/or malononitrile. vii Another base catalyst, KF supported on alumina, was investigated for the synthesis of pseudoionone by the aldol condensation of citral and acetone. After optimization of parameters, including acetone/citral ratio, reaction temperature and the catalyst amount, a very high selectivity of 95% to the desired product, pseudoionone, was obtained with 90 % conversion using a commercially available catalyst. Studies of the loading of KF on alumina showed that a loading of 8.5 mmol KF/g was even better with an excellent citral conversion 99% with 97% selectivity to pseudoionone. More importantly, the catalyst could be used as-synthesized without any pretreatment or activation procedure. This is clearly advantageous from a practical point of view. In the study on oxygen storage materials, nanocrystalline cerium-zirconium mixed oxides were prepared by the precipitation of hydroxides that were then subjected to hydrothermal treatment at 100 °C for to days. Hydrothermal digestion led to ceria-zirconia with higher surface area and thermal stability than the untreated oxide. These samples were more reducible as oxygen could be removed at a lower temperature than for the untreated ceria-zirconia. Despite calcination at 1000 °C, the surface area of the hydrothermally synthesized samples remained relatively high at ~11–12 m2/g while the untreated Ce0.5Zr0.5O2 had only 4.2 m2/g. The continuous dissolution and reprecipitation of hydroxides during hydrothermal treatment is postulated to give a more defect-free structure which is able to withstand loss of surface area when exposed to high temperatures. The addition of silica to ceria-zirconia further increased the surface area and the oxygen storage capacity. Hydrothermally treated wt% Si loaded ceria zirconia samples had OSC values of 0.65-0.69 mmol O2/g, which indicates that about 77-80% of the cerium can be reversibly reduced and reoxidized at 700 °C. However, the silica- viii containing oxides suffered severe loss in surface area after calcination at 1000 °C. The XPS studies revealed the formation of a surface overlayer of zirconium-rich silicate phase which possibly decreased the oxygen storage capacity. The addition of Fe is also helpful to a higher oxygen storage capacity. Under oxidizing conditions, iron acts as an additional oxygen storage component through the multiple oxidation state of Fe. The OSC shows a strong dependence on surface area for ceria–zirconia with less than 50 m2/g but for high surface area oxides, the amount of exchangeable oxygen is limited by the intrinsic reducibility of the material. ix 9.50E-12 8.50E-12 (a) CO2 signal (A) 7.50E-12 (b) 6.50E-12 (c) 5.50E-12 4.50E-12 (d) 3.50E-12 (e) 2.50E-12 1.50E-12 5.00E-13 100 (f) 200 300 400 500 600 700 Temperature (°C) Figure 7-21. CO2 signal during TPR of (a) CZ-H-4, (b) 1%Si-CZ-H-4, (c) 2%Si-CZH-4, (d) 4%Si-CZ-H-4, (e) 5%Si-CZ-H-4 and (f) 10%Si-CZ-H-4. 203 9E-12 CO2 signal (A) 7E-12 (e) (d) 5E-12 (c) (b) 3E-12 (a) 1E-12 150 250 350 450 550 650 Temperature (°C) Figure 7-22. CO2 signal during TPR of (a) 4%Si-CZ-H-0 (b) 4%Si-CZ-H-1 (c) 4%SiCZ-H-2 (d) 4%Si-CZ-H-4 (e) 4%Si-CZ-H-8. 204 OSC (mmol O /g) 1.1 0.9 0.7 0.5 0.3 350 450 550 650 750 o Temperature ( C) Figure 7-23. Oxygen storage capacity at different temperatures for 2%Fe-CZ-H (dotted lines) and 4%Si-CZ-H (full lines) hydrothermally treated for (■, □); (); (●, ○); (, ); and days (, ). 205 1.0E-11 9.0E-12 (f) CO2 Signal (A) 8.0E-12 7.0E-12 6.0E-12 (e) 5.0E-12 (d) 4.0E-12 (c) 3.0E-12 (b) 2.0E-12 1.0E-12 0.0E+00 100 (a) 200 300 400 500 600 700 Temperature (°C) Figure 7-24. CO2 signal during TPR of (a) 0%Fe-CZ-H-4 (b) 0.3%Fe-CZ-H-4 (c) 0.5%Fe-CZ-H-4 (d) 1%Fe-CZ-H-4 (e) 2%Fe-CZ-H-4 (f) 5%Fe-CZ-H-4. 206 2.2E-11 CO2 Signal (A) 2E-11 1.8E-11 (c) 1.6E-11 (b) 1.4E-11 1.2E-11 1E-11 100 (a) 200 300 400 500 600 700 Temperature (°C) Figure 7-25. CO2 signal during TPR of 2%Fe-CZ-H-4 (a) Run-1 (b) Run-2 (c) Run-3. 207 8.0E-12 7.0E-12 (e) CO2 Signal (A) 6.0E-12 5.0E-12 (d) 4.0E-12 (c) 3.0E-12 (b) 2.0E-12 (a) 1.0E-12 0.0E+00 100 200 300 400 500 600 700 Temperature (°C) Figure 7-26. CO2 signal during TPR of (a) 2%Fe-CZ-H-0 (b) 2%Fe-CZ-H-1 (c) 2%Fe-CZ-H-2 (d) 2%Fe-CZ-H-4 (e) 2%Fe-CZ-H-8. 208 3E-12 Ion current (A) 2.5E-12 2E-12 1.5E-12 (b) (d) 1E-12 (a) (c) 5E-13 100 200 300 400 500 600 700 o Temperature ( C) Figure 7-27. CO2 signal during TPR of (a, c) CZ-H-0 and (b, d) CZ-H-4 calcined at 500 C and 1000 C, respectively. 209 3.5E-12 3E-12 CO2 Signal (A) 2.5E-12 2E-12 (b) 1.5E-12 1E-12 (a) 5E-13 100 (d) (c) 200 300 400 500 600 700 o Temperature ( C) Figure 7-28. CO2 signal during TPR of (a, c) 4%Si-CZ-H-0 and (b, d) 4%Si-CZ-H-8 calcined at 500 C and 1000 C, respectively. 210 1350 950 750 Counts/s 1150 (b) 550 (a) 350 105 104 103 102 101 100 99 Binding energy (eV) Figure 7-29. Si 2p XPS spectra of 4%Si-CZ-H-O after calcination at (a) 500 C (b)1000 C. 211 0.8 OSC (mmol O /g) 0.7 0.6 0.5 0.4 0.3 350 450 550 650 750 o Temperature ( C) Figure 7-30. 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In contrast, fewer efforts have been made to study solid base catalysts Comparing the industrial applications of solid acid and base catalysts, only 8% of the processes employ solid base as catalyst [1] There are, however, numerous reactions such as isomerization, additions, alkylations and cyclizations, which are carried out industrially using liquid base 1 catalysts Solid base catalysts have many... as reduced corrosion and environmental problems Solid acid and base catalysts have been used in many industrial processes and their surface properties and structures have been analyzed by newly developed instruments and highly sophisticated techniques 1.2 Solid base catalysts Solid acid catalysts have been extensively studied in the past 40 years due to the demand in the petroleum and petrochemical industries... over liquid bases or organometallics as they present fewer disposal problems while allowing easier separation and recovery of the products, catalyst, and solvent They are also noncorrosive Thus, solid base catalysts offer environmentally benign and more economical pathways for the synthesis of fine chemicals The replacement of liquid bases by solid base catalysts not only allow easy separation and recycle... many cases, the possibility to prepare solid base catalysts with different nature of active sites (Brønsted or Lewis sites), and with a wide range of basic strengths Because of these advantages, research on the synthesis of fine chemicals using solid bases as catalyst has increased over the past decade 1.3 Types of solid base catalysts The study on the solid base catalysts was started by Pines et al... usually in the solid phase, thus heterogeneous catalysts are also known as solid catalysts The increasing social and environmental pressure on the industry to substitute the traditional homogeneously-catalyzed reactions with environmental friendly technologies is the driving force for the development of heterogeneous catalyst Indeed, solid catalysts have many advantages over liquid catalysts, such... (Na/NaOH/γ-Al2O3), alkaline earth solids such as magnesium and barium oxides, and aluminum magnesium mixed oxides derived from hydrotalcites [8] and nitrides [9] 2 1.3.1 Metal oxides Alkaline earth metal oxides such as MgO and CaO are active solid base catalysts for various reactions The catalytic activity of MgO and CaO prepared from Ca(OH)2 and Mg(OH)2 depends very much on the pretreatment temperature... at ambient temperature and appreciable conversion and selectivity were observed 9 1.4 Applications of solid base catalyst for organic reactions Bases are usually used in organic reactions to deprotonate and form carbanion intermediates In the field of fine chemicals production, important steps in the synthesis of relatively large and complex molecules include carbon-carbon bond forming reactions such... that are formed at high temperatures should be stronger than those formed at lower temperatures However, often, rearrangement of surface and bulk atoms may occur during pre-treatment, thus changing the number and nature of the surface basic sites MgO and CaO free from impurities are superbases, which is defined as materials having basic sites with the Hammett constant ≥ 26 CaO and MgO are useful catalysts. .. ceria-zirconia 179 Table 7-4 XPS electron binding energies (eV) and atomic ratio of ceriazirconia mixed oxide 180 Table 7-5 Activity for isopropanol dehydration over various ceriumzirconium mixed oxides 181 Table 7-6 Oxygen storage capacity at 700 C 182 Table 7-7 Oxygen storage capacity at 700 °C 183 Table 7-8 Oxygen storage capacity at 700 °C for iron-doped ceria-zirconia samples 184 xiii List of Schemes... peroxide by solid base catalysts Vadivukarasi Raju and G.K Chuah (Poster at the Singapore International Chemical Conference SICC-4, 8-10 December 2005, Singapore) 2) Epoxidation of olefins with hydrogen peroxide over solid base catalysts Vadivukarasi Raju, G.K Chuah (Poster at the Asia Pacific Congress on Catalysis APCAT-4, 6-8 December 2006, Singapore) 3) Influence of preparation conditions and silica . oxides as solid base catalysts and as oxygen storage material. Solid base catalysts are widely used for the synthesis of fine chemicals because of their environmentally benign nature and the possibility. Introduction 1 1.2 Solid base catalysts 1 1.3 Types of solid base catalysts 2 1.3.1 Metal oxides 3 1.3.2 Supported catalysts 3 1.3.3 Basic zeolites 5 1.3.4 Mesoporous materials 6 1.3.5. MATERIALS FOR SOLID BASE CATALYSTS AND OXYGEN STORAGE VADIVUKARASI RAJU