Reactivity of metal oxyhydroxides for organic tandem conversions

Abstract

The thesis is divided into a total of 6 chapters and the organization of each chapter is given below. Chapter 1: This chapter gives introduction to Metal Oxyhydroxides, their structures, synthesis method, available applications. A literature review of heterogeneous tandem catalysis is also discussed with comparative study on the active sites responsible for catalysis. This chapter also deals with analytical tools required for characterization of metal oxyhydroxides and the tandem catalysis products. This Chapter also provides the blueprint about the intent of the thesis. Chapter 2: A study of acid-base behaviour of hierarchically condensed phases consisting of Hydroxides, Oxyhydroxides and Oxides of Cr, Mn, Co, Al was done. All the three phases M(OH)x, MO(OH) and Mx(O)y show acid-base bifunctional behavior to varying extent. The strength of acid sites is stronger on MO(OH) while the strength of basic sites is stronger on M(OH)x. MO(OH) are versatile due to its stability and two types of active sites OH/O- and O2- Chapter 3 is divided into two sub chapters 3a & 3b dealing with acid-base properties of FeO(OH) Chapter 3a: A study of acid-base behaviour of polymorphs of FeO(OH) was undertaken in this chapter. Within a same FeO(OH), its polymorphs α, β, γ and δ all show bifunctional acid-base reactivity. The origin of acid and base bifunctional property is due to the surface chemical equilibrium between FeO(OH) and FeOO groups. The difference in the selectivity with the polymorphs is probably due to the different types of FeO(OH) sites and the density of the sites present on the crystal facets of the polymorphs. Chapter 3b: In this chapter, γ-FeO(OH) was demonstrated as an efficient solid base catalyst for the synthesis of pseudoionones (PS). High activity can be attributed to the formation of chemically stable Brønsted basic sites (-O - ) of the surface hydroxyl Chapter 1 2020-Ph. D. Thesis: Mr. Dnyanesh Vernekar, CSIR-NCL, AcSIR 30 groups. In the presence of water, there was an enhancement of catalytic activity by several folds due to the generation of basic sites. Chapter 4 is sub divided into 4a & 4b dealing with redox-base property of metal oxyhydroxides Chapter 4a: This chapter deals with sequential transformation of benzyl alcohol to a variety of C-C and C-N coupling products on layered K-α-CrO(OH). The transformations were feasible because of the co-existence of redox Cr(III) and basic sites (O- and O2- ) on the surface of the K-α-CrO(OH). The presence of electron rich sites (O2- ) due to doping of K and the surface hydroxyl groups were found to be the basic sites on the catalysts using spectroscopy and thermal probe studies. Chapter 4b: A study on usefulness of oxide-oxyhydroxide interface was carried out over a defect manganese oxyhydroxide sample MnOx(OH). An oxide impurity in MnOx(OH) was identified and thoroughly characterized. Its effect on sequential oxidation-condensation reaction was studied and its superiority over a pure MnO(OH) catalyst was explored. The oxide impurity increased O2- basic sites on MnOx(OH). Chapter 5: This chapter studies a mixed metal oxyhydroxide WFeCoO(OH) for catalytic conversion of cyclohexane to adipic acid conversion in one pot. A high surge in Lewis acidity was obtained by W doping in Co-Fe matrix. The high acidity and W sites are responsible for activity. DFT calculations indicated a decrease in deprotonation energies for WFeCoO(OH) as compared to undoped CoO(OH). Chapter 6: This chapter to gives summary and future scope of the present work.