Development of heterogeneous catalytic systems for the transformation of carbon dioxide to methanol under mild conditions.

Rising level of carbon dioxide (CO2) is a significant contributor to global warming and poses a major concern in modern society and environment. Anthropogenic activities such as fossil fuel combustion, cement production and deforestation are the primary causes of CO2 emissions. Creating sustainable pathways by converting abundantly available CO2 into fuel could help in mitigating the ever-growing global energy demand. Owing to the high intrinsic thermodynamic stability of CO2 molecule, the chemical reduction mechanism requires an appropriate catalyst system to reduce the high activation energy barrier. Additionally, the prospect of utilising CO2 as C1 synthon to convert the amines to afford value-added formamides is even more appealing. In the present dissertation, the development of efficient industrial friendly heterogeneous catalytic routes for CO2 fixation on amines by chemical reduction method to formamides, as well as their subsequent conversion to fuel, methanol under mild conditions are investigated. The first chapter describes an overview about the current trends in global climate change, about the challenges in CO2 capture and storage, the employment of CO2 as a source of carbon to synthesise industrially essential formamide products by catalytic reduction. Subsequently, the reduction pathway of formamides to afford methanol is also elucidated. Additionally, the prospect of using formic acid (a known CO2 and H2 carrier) to formylate amines and the consequent reduction to methanol is also given. The combination of these reactions presents a viable CO2 reduction system using amines. In the second chapter, N-formylation and N-methylation of amines using CO2 as the carbon source catalysed by palladium nanoparticles (Pd NPs) under mild conditions are discussed. The concluding results point out the high efficiency and high selectivity of Pd NPs in catalysing the amines to fix CO2 to afford formamides at room temperature. The Pd NPs exhibited excellent catalytic activity and selectivity on par with the reported catalysts. The overall selectivity and conversion of the products could be altered by adjusting the CO2 pressure, catalyst loading, temperature and solvent. The catalyst could be recycled for multiple reactions without significant loss of activity. The third chapter describes a ‘Geo-inspired’ catalyst system with the use of an iron-rich natural mineral-Gibeon meteorite, as the catalyst for N-formylation and N-methylation of amines using CO2 as the carbon source at room temperature. Similar to the second chapter, the Gibeon meteorite exhibited excellent catalytic activity and selectivity on par with the reported catalysts. The overall selectivity and conversion could be altered by adjusting the CO2 pressure, catalyst loading, temperature and solvent. Comparative studies with the similar iron-containing alloys were also carried out. A plausible mechanism is proposed with the Gibeon meteorite’s surface bound hydroxide ions. Moreover, the catalyst could be easily recovered and reused for multiple reactions as well without significant loss of activity. The fourth chapter encompasses the investigation of a metal-free catalytic system using polymerisable ionic liquid- (4-Vinylbenzyl)trimethylammonium chloride catalysed N-formylation and N-methylation of amines using CO2 as the carbon source under mild conditions. Similar to second and third chapters, the monomer and the polymer exhibited excellent catalytic activity (comparable