Design of functional metal-organic frameworks for catalytic conversion of CO2 to value-added chemicals

Abstract

The immense amount of carbon dioxide (CO2) emissions has resulted in the most serious environmental issues like ocean acidification, extreme weather, species extinction, and global warming. Consequently, the utilization of carbon dioxide as C1-feedstock offers the dual advantages of mitigating the increasing atmospheric CO2 concentration and production of valuable chemicals. However, the inertness of carbon dioxide puts a significant challenge to its functionalization at ambient conditions. Thus, the majority of the catalytic systems reported for fixation of carbon dioxide require either high temperature and/or high pressure of CO2 and often additional co-catalysts are employed. However, towards green and sustainable utilization of carbon dioxide, it is highly desirable to carry out the transformation under co-catalyst-free mild conditions. In this context, metal-organic framework (MOF)-based catalysts have shown unique advantages over other conventional porous materials due to their tunable pore size and functionality along with high surface areas. The thesis work has been divided into six chapters. The Chapter 1 includes introduction to framework materials and importance of carbon capture/utilization and various strategies employed for chemical fixation of CO2 to high-value chemicals and fuels under environment-friendly mild conditions. Further, with the aforementioned motivation for capture and utilization of CO2 as C1-feedstock to generate various high-value chemicals, we rationally designed MOF-based heterogeneous catalysts for effective conversion of carbon dioxide under eco-friendly conditions. In this regard, the work carried out in Chapter 2 includes rational design of catalytic MOFs based on Lewis acidic Zn(II) and organic linker composed of basic sites suitable for effective fixation of CO2 to value added cyclic carbonates at mild conditions. Notably, the utilization of carbon dioxide from direct air has attracted tremendous attention as this process enables carbon capture from any place independent of emission sources. In this context, by utilizing reticular synthesis, we strategically designed a Mg-based highly MOF with pores functionalized with CO2-philic sites for chemical fixation of CO2 from air into high-value cyclic carbonates at mild conditions which will be presented in Chapter 3. Besides, the sunlight-driven fixation of CO2 into valuable chemicals constitutes a promising approach toward a sustainable generation of valuable chemicals over the traditional thermal-driven process. In this regard, in Chapter 4, Mg-centered porphyrin MOF having relevance to chlorophyll in green plants was developed and its application for visible light promoted effective fixation of CO2 was investigated. Encouraged by the unique advantages of MOFs towards the stabilization of catalytically active metal ions, the post-synthetic functionalization of NHC-based MOFs with catalytically active Ag(I)/Cu(I) species and their catalytic activity for CO2 fixation is presented in Chapter 5. These Ag(I)/Cu(I) anchored NHC-MOFs were utilized as recyclable catalysts for the transformation of carbon dioxide to α-alkylidene cyclic carbonates and oxazolidinone, an important building block for antibiotics under mild conditions. Further, towards photocatalytic reduction of CO2 to valuable chemicals and fuels, in Chapter 6, design of 2D Co-based porphyrin network and its photocatalytic performance for carbon dioxide reduction is reported. Overall, the work carried out in the thesis involving the strategic design of framework materials and their catalytic investigation for chemical fixation of CO2 to high-value chemicals.