Thesis 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).

Thesis Overview

1. 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:

• Increase of available surface
• Stabilization against crystal growth and sintering
• Creation of a favourable orientation of surface molecules
• Improvement of mechanical strength

Nickel-silica catalysts have potential application generally for hydrogenation4,5; also in petrochemical industry for processes like deoxygenation, methanation, reforming, and hydro-cracking6.

The existence of raw sand with proper composition and catalytic ability has been reported; the sand was treated and used to accomplish the catalysis of Friedel Crafts acylation7.

Catalysts are employed in many industrial processes; special mention is made of the processes for the manufacture and upgrading of motor gasoline. This industry is by far the largest user of catalyst and has been the inspiration for much of the progress in the development of catalysts and the techniques of their manufacture and use8.

Steps involved in catalyst development are as follows:

• Choice from previous knowledge, of the elements or compounds known to be effective in reactions of the type under consideration;
• Narrowing down by actual experimental test, of the list of possible catalysts to identify those that are most promising;
• Attempting to improve the performance of the catalysts selected by preparing and testing their mixture, by subjecting them to treatments designed to increase their specific surface area, by trying different activation methods, and by varying the size of the catalyst particles;
• Attempting to characterise the detailed form and structure, as well as the properties of the catalyst and to correlate them with the performance of the catalyst.

1.2 Statement of Problem

The use of imported catalyst is the order of the day. In our research lab; the small scale reactions employ expensive imported catalyst, likewise our chemical industries that produce in large scale.

Silica is cheap and readily available, but it is imported; intensive research on purifying our local soil and producing silica based products from it is needed to put our raw materials to use.

Although many efficacious catalysts exist and nickel-silica (Ni-SiO2) has been synthesized6, there is need to develop the best of the catalyst by trying different methods of preparation and comparing their products. Presently, no combined silica catalysts have been synthesized employing silica from our local soil, to the best of our knowledge.

1.3 Research Objectives

This work is aimed at:

• Testing different soil samples with the aim of selecting the sample with the best surface features for catalyst application;
• Purification of the samples using both physical means and chemical leaching into silica; this makes it suitable for application in many chemical industries/processes;
• Development of nickel-silica catalyst using silica from the locally available soils by co-precipitation and deposition methods;

• Physico-chemical characterisation of the prepared nickel silica catalysts; and

•  Optimization of preparation method for the nickel-silica catalyst and comparing the effect of two nickel precursors on the final product.

1.4       Justification of the Study

The successes of basic research in the field of catalysis have direct effect on solving many fundamental problems that face humanity. Examples of such solutions include: efficient utilisation of raw materials, mastering of new sources of energy and improvement on the existing ones, and development of efficient systems for environmental protection3.

Due to high cost of running high temperature engines coupled with the long duration of some chemical reactions, it becomes imperative to resort to use of catalysts to speed up such reactions. It is also unreasonable to import expensive and non-specialty catalysts while their alternatives could be synthesized locally.