Design of Zeolite Catalysts for Selective CO₂ Hydrogenation and Alcohol Production

The primary objective of this dissertation is to investigate the application of zeolites as catalyst supports to facilitate the conversion of CO₂ into alcohols, particularly ethanol, a highly desirable chemical. Considering the critical need to combat greenhouse gas emissions, specifically CO₂ generated from the burning of fossil fuels, it is imperative to establish effective and sustainable catalysts for converting it into valuable chemicals, such as alcohols.
Chapter 1 provides an overview of the process involving the hydrogenation of CO₂. Additionally, it discusses zeolites and their distinctive attributes that make them suitable for use in heterogeneous catalysis, along with various methods of synthesis. The chapter concludes by introducing the late research on zeolite catalysis to produce ethanol from CO₂ and outlining the scope of this thesis.
Chapter 2 explores various essential characterization methods, including powder X-ray diffraction, electron microscopy, NH₃-TPD, N₂ physisorption, and X-ray absorption spectroscopy.
Chapter 3 presents the results published in ChemPlusChem (Paper 2). The research focuses on assessing the effect of introducing mesopores into ZSM-5, S1, and Beta zeolites containing Cu nanoparticles and their use for the direct conversion of CO₂ into alcohols. The investigation highlighted the crucial role of polar solvents, particularly water, in enhancing alcohol yields. It also revealed the influence of mesopores on product selectivity, particularly in ethanol production.
Chapter 4 explores Cu-based MOR zeolites and evaluates three distinct methods for incorporating Cu within the MOR structure. The methods included conventional hydrothermal synthesis, impregnation, and steam-assisted interzeolite transformation of FAU. The results detailed in Chapter 4 pertain to a manuscript under preparation for submission (Paper 3). 
Chapter 5 investigates Cu nanoparticles encapsulated within the channels of the GME framework, and their catalytic potential for CO₂ hydrogenation. The catalytic performance was assessed in a Micromeritics flow reactor, revealing promising results for ethanol production under optimized conditions. Thorough characterization provided insights into the catalysts' structural and electronic properties, emphasizing the synergistic interaction between Cu dimers and the GME framework as a key factor influencing catalytic performance. The results presented in Chapter 5 have been patented under the European patent application number 23386053.5, titled "Conversion of CO₂ to alcohols using zeolite catalysts". 
Chapter 6 addresses the challenges of GME’s instability and deactivation through thorough investigations. The chapter explores the role of defects within the zeolite and their impact on catalyst stability. Additionally, it discusses the application of silylating agents to create a hydrophobic layer around the material, aiming to protect the catalyst under reaction conditions. Finally, it investigates the influence of calcium within the zeolite pores, exploring the effects of various alkali metal cations as stabilizers for GME channels and promoters for CO₂ hydrogenation. The results described in Chapter 6 are included in a manuscript under preparation for submission (Paper 4).
Chapter 7 examines Cu-containing CHA catalysts, revealing the presence of isolated Cu²⁺ complexes and their influence on product selectivity in CO₂ hydrogenation. The role of alkali metal promoters in modulating selectivity towards ethylene and ethane is elucidated, offering valuable insights into the behavior and catalytic performance of Cu-containing CHA catalysts.
In Chapter 8, a comprehensive summary of all preceding chapters is provided, offering a cohesive overview of the research journey. This summary encapsulates the key findings, methodologies, and conclusions explored throughout the thesis, providing the reader with a holistic understanding of the study's progression.