ABSTRACT
The efficacy of silica obtained from our local sand as a carrier in synthesis of Nickel-Silica catalyst was investigated. Six samples of soil were collected from two different sites (comprising five white coloured samples collected from Iva valley, lower part of Milliken hill, namely: pottery 2 (P2), down iva (DI), run-off iva (ROI), pottery rock (POR), white chalk (WTC) and one brown coloured sample (UdS) collected from Udi Siding) in Enugu, Nigeria. Prior to treatment by flotation method, some properties that could affect their catalytic use like organic matter content, texture, porosity and pH were assayed. (i) P2 (pH, 4.7; fine sand, 74.29 %; organic matter, 0.26 %), (ii) DI (pH, 4.7; fine sand, 72.72 %; organic matter, 0.26 %), (iii) ROI (pH, 7.4; fine sand, 87.42 %; organic matter, 0.19 %), (iv) POR (pH, 6.4; fine sand, 85.65 %; organic matter, 0.0%), (v) WTC (pH, 4.7; fine sand, 83.59 %; organic matter, 0.07 %) and (vi) UdS (pH, 4.4; fine sand, 32.79 %; organic matter, 0.19 %). Three of the samples with the best results ROI, POR, and WTC as can be seen above were selected. The pre-treated sand was purified by leaching process using 20 % HF, 20 % H2SO4, 10 % NaOH and distilled water. Comparison of the XRD results of the raw sand sample and silica extract showed complete removal of Al, Ca, and other oxide impurities from the raw sand. The silica was coupled with nickel employing two catalyst preparation methods. The Deposition method was used to couple silica with Ni(NO3)2 to prepare the catalyst named DPNN and NiCl2 to prepare the catalyst named DPNC. In the Co-precipitation method, silica was coupled with NiCl2 to prepare the catalyst named CPNC. The surface area, pore volume and particle size distributions of the catalyst samples were determined by N2 adsorption at 77 K using Trister II Plus BET analyzer. The elemental composition was obtained by XRF spectroscopy. Effect of using two different nickel precursors for coupling was investigated; the result showed that NiNO3 gave a higher degree of Ni dispersion and incorporation compared to NiCl2. Effect of using two different catalyst preparation methods was also investigated; Co-precipitation method allowed the highest degree of Ni incorporation and improved surface properties. The results showed that Ni-silica catalysts prepared using silica from the local soil has catalytic properties that are similar to the standard Ni-Silica catalyst, Euro Ni-1, and better catalytic properties than some previously synthesized ones reported by Unichema, C. B. V. (1990), Wang, W. et al (2006), and Hermida, L. et al (2012).
TABLE OF CONTENTS
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Abstract vi
Table of contents vii
CHAPTER ONE: INTRODUCTION
1.1Background of the study 1
1.2Statement of the problem 2
1.3Objectives of the study 3
1.4Justification of the study 3
CHAPTER TWO: LITERATURE REVIEW
2.1 Sand and Silica 4
2.2 Development of catalyst 11
2.3 Physical properties of white sand that affect its catalytic use 17
2.3.1 Texture of white sand 17
2.3.2 Porosity of white sand 20
2.3.3 Specific surface area 23
2.3.4 Pore sizes 27
2.4 Chemical properties of white sand that affect its catalytic use 30
2.4.1 pH 30
2.4.2 Silica content 31
2.4.3 Organic matter 33
2.5 Industrial applications of silica 34
2.5.1 Production of glass 34
2.5.2 Catalyst 36
2.5.3 Silica gel and household items like toothpaste, slippers, etc 37
2.5.4 Food processing 38
2.6 Preparation of the catalyst 40
2.7 Components of the catalyst formulation 43
2.8 Review of previous works on catalysis 44
CHAPTER THREE: EXPERIMENTAL
3.1 Materials and Equipment 48 3.1.1 Materials 48
3.1.2 Equipment 49
3.2 Sampling 50
3.3 Sample preparation 50
3.4 Test for pH 50
3.5 Determination of texture 51
3.6 Determination of porosity 52
3.7 Determination of organic matter content 52
3.8 Extraction of silica using leaching process 53
3.9 X-Ray Diffraction analysis of raw sand and extracted silica 54
3.10 Coupling of Nickel and silica 54
3.10.1 Co-precipitation method 54
3.10.2 Deposition method 54
3.11 Characterization of Ni-silica catalyst 55
3.11.1 Elemental composition by X-Ray Fluorescence 55
3.11.2 Surface Properties 55
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Porosity, Texture, pH and Organic matter of raw sand 56
4.1.1 Porosity 56
4.1.2 Textural Class 57
4.1.3 pH Results 58
4.1.4 Organic Matter 58
4.2 XRD results of raw sand and the obtained silica 59
4.3 Results of characterisation of the Nickel-Silica catalyst 62
4.3.1 XRF 62
4.3.2 Surface area, Pore sizes, Particle sizes, and Pore volume 63
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 65
5.2 Recommendations 65
REFERENCES 66
APPENDICES
Appendix A1: XRD data of raw soil 73
Appendix A2: XRD data of the silica extract from the raw soil 75
Appendix B: Original copy of XRF result of the three catalyst samples 78
Appendix C: Nitrogen adsorption data 79
LIST OF FIGURES Page
Figure 2.1: Sandy soil 4
Figure 2.2: An electron micrograph showing grains of sand 5
Figure 2.3: Molecular structure of silica 7
Figure 2.4: World consumption of silica in 1990 10
Figure 2.5: Reaction energetics 16
Figure 2.6: Soil Textural Triangle 19
Figure 2.7: Example of soil core sampler 20
Figure 2.8: Optical method of measuring porosity 22
Figure 2.9 TriStar II PLUS Nitrogen Adsorption Instrument 24
Figure 2.10: Graphical representation of BET equation/ Plot of Nitrogen adsorption isotherm 25
Figure 2.11: Graph of Pore size distribution measurement 28
Figure 2.12: Graph of mercury intrusion method for measuring porosity 30
Figure 2.13: Pack of Silica gel 37
Figure 2.14: Silica 39
Figure 4.1: XRD Patterns of Raw Sand 60
Figure 4.2: XRD Patterns of the Purified Sand (Silica) 61
LIST OF TABLES Page
Table 2.1: Some Physical Properties of Crystalline and Amorphous Silica 8
Table 2.2: Chemical Properties of Silica 9
Table 2.3: The Particle Size of Sand, Silt and Clay 18
Table 3.1: Materials 48
Table 3.2: Equipment 49
Table 4.1: Porosities from Bulk Densities of the Soil Samples 56
Table 4.2: Sand Content of the Soil Samples from Texture Measurements 57
Table 4.3: pH Results of the six Soil Samples 58
Table 4.4: Organic Matter Content of the Soil Samples calculated from % Organic Carbon 58
Table 4.5: Elemental Composition of the synthesized Catalysts calculated from their Oxides given in XRF Results 62
Table 4.6: Surface area, Pore sizes, Pore volume and Particle size Results of WTC Silica and the three Nickel-Silica Catalyst Samples 63
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF STUDY
The search for catalysts or improved catalysts seems to be a never ending one since small reductions in operating temperature and pressure, or small differences in yields or product distribution affected by catalysts can have great economic importance on the commercial scale.
Catalysts are chemical substances that modify the rate of a chemical reaction, usually by acceleration; while catalysis is the process in which the rate of a chemical reaction is influenced by a catalyst1,2. Examples of catalysts include hydrogen ion, Vanadium (v) Oxide, nickel etc. Industrial catalytic processes includes: hydrogenation of oils, Ammonia synthesis, cracking of petroleum, Friedel Crafts reaction etc.
In most cases, industrial catalysts contain 3 groups of components: catalytically active materials, catalyst support and promoters. Catalytically active material is a precursor to industrial catalyst; they possess appropriate catalytic properties (activity and selectivity) but still do not have the complex of properties required for industrial catalyst. The complex of properties include proper pore structure, long lifetime, high resistance to deactivation and poisons, easy regeneration, low operating temperature, high thermal stability, high mechanical strength, resistance to attrition and low price3.
Sand is everywhere around us, not often used in the chemistry laboratory as it contains a lot of impurities. Adding value to sand by purification turns it into silicon dioxide which has many applications in chemistry. Furthermore, combination of silica with some catalytically active substances like alumina, nickel, platinum, copper etc makes it improved catalyst with better activity and evenly dispersion of the active agent on the carrier. Improvements that may result from dispersion of the catalytically active agent include:
