Functionalization of porous inorganic materials and their applications in catalysis

Abstract

This work aims at preparing highly efficient robust monometallic as well as bimetallic supported transition metal based nanocatalysts. The unsupported nanocatalysts derived from metal and/ metal oxide tend to aggregate in the native state, prone to oxidation and thereby affect the stability and reusability following drastic fall in catalytic activity. It is also known that precious metals like Au, Pt, Pd and Ru possess comparatively better catalytic activity, but they are expensive, requiring expensive precursor salts. In order to achieve comparable catalytic performance like precious metal based nanocatalysts, three different nanocatalytic systems derived from transition metals (Cu, Cu-Ni and Cu-Ag) supported on magnetic or nonmagnetic mesoporous SiO2 support are synthesized, characterized, evaluated and finally compared. For simplification and clear understanding this thesis has been divided into Seven chapters. Chapter 1 is focused on general introduction covering importance of catalysis, catalysis types, classification of catalysts, monometallic and bimetallic catalysts and the role of metal nanoparticles (NPs) as catalysts in chemical reactions. This chapter also introduced the use of supporting materials like silica, metal oxide and graphite, the modification of supporting materials, and the mechanism of the formation of mesoporous silica. A brief objective of the present investigation is discussed towards the end of this chapter. Chapter 2 described the preparation of stable suspension of copper nanoparticles (CuNPs). Mesoporous amine functionalized silica (SiO -NH ) particles have been used as platform to house CuNPs for preventing their agglomeration. Mesoporous SiO2-NH2 particles are first prepared in one pot by diethyl amine, DEA catalyzed hydrolysis and condensation of tetraethyl orthosilicate, TEOS precursor in presence of hexamethylene diamine, HMDA and cetyltrimethyla-mmonium bromide, CTAB. In the second step, sequential adsorption and chemical reduction of Cu ions are carried out to obtain SiO2- NH /Cu nanocatalyst. The morphology and structural composition of SiO -NH /Cu nanocatalyst confirmed the fixation of evenly distributed ~ 28 nm sized Cu particles. The catalytic activity of nanocomposite particles for reductive degradation of Congo Red, CR and Eriochrome Black-T, EBT showed maximum degradation at pH values of 7 and 4, respectively. The degradation efficiency increased with the increase in catalyst dose and a activity and recycle stability of bimetallic Cu-Ni nanocatalyst enhanced dramatically following the use of magnetic Fe O -SiO -NH composite support. Additionally, the prepared Fe O -SiO -NH /Cu-Ni nanocatalyst possessed good application potential as antibacterial agent due to the presence of Cu-Ni. nanocomposite support is used to anchor bimetallic Cu-Ag alloy NPs using glucose as a green reducing agent. SiO /Fe O -SiO -NH nano-composite support is prepared in one- pot via simultaneous co-precipitation of iron salts and alkaline hydrolysis-condensation reaction of TEOS in presence of SiO2 sphere. HMDA and CTAB are used as functional agent and structure directing agent, respectively. Finally, Cu-Ag NPs are formed on the functional nanocomposite support via in-situ green reduction protocol to obtain SiO /Fe O -SiO -NH /Cu-Ag nanocatalyst. A comparative study of catalytic reduction of calcination. The incorporation of magnetic Fe O in the SiO /SiO -NH support material also considerably enhanced the catalytic property of the nanocatalyst. The reduction reaction favorably followed pseudo-first-order kinetic rate model and the rate constants of non-calcined and calcined SiO /Fe O -SiO -NH /Cu-Ag nanocatalysts are 0.0517 and

0.0998 min−1, respectively. The magnetically separable non-calcined SiO /Fe O -SiO2 NH2/Cu-Ag nanocatalyst is recyclable up to five cycles with fairly acceptable conversion. Chapter 6 provides a general comparison among various supported and unsupported prepared bimetallic and monometallic nanocatalysts. The role of different support materials on catalysis are also taken into account for drawing an overall hypothesis. The reduction rate of 4-NP to 4-AP, recycle stability as well as recoverability have been used as the basis for such comparison. It is evident that Fe O -SiO -NH 2 composite support enhanced the recycle stability and long-term durability over the other support (SiO -NH /Cu-Ni) due to the inclusion of magnetic (Fe O ) particles. Comparative study also shows that bimetallic Cu-Ni NPs supported on Fe O -SiO –NH2

composite possessed better catalytic activity. Chapter 7 gives a short conclusion, and proposed a hypothesis model. Overall, it is found that incorporation of magnetic Fe O in mesoporous amine functional SiO2 support improved the catalytic activity and stability of anchored metal nano-catalyst. Amine functionality in SiO2 support also played a positive role in enhancing the overall catalytic performance of the anchored NPs. However, for generalizing this hypothesis, a study of few other catalyst systems is necessary.