Design, Synthesis, and Evaluation of Bio-based Catalysts for Green Oxidation Reactions

Thesis Abstract

Development of sustainable catalytic systems for green oxidation processes addresses the pressing need to reduce reliance on precious metal catalysts and harsh oxidants in fine chemical synthesis. The study aims to design, synthesize, and evaluate bio-based catalysts derived from ubiquitous renewable polymers and natural enzymes, to achieve high activity, selectivity, and reusability under mild conditions. Specific objectives are (1) to synthesize a library of bio-based catalysts by functionalizing chitosan, lignin, and cellulose with non-precious metal centers (Fe, Cu, Mn) and enzyme-mimetic motifs; (2) to characterize structural, surface, and electronic properties using FTIR, solid-state NMR, X-ray diffraction, BET surface area, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM); (3) to optimize catalytic performance in representative green oxidation reactions (upcycling of primary alcohols to aldehydes and ketones, oxidation of aldehydes to acids, and hydroxylation of diverse alkanes) using hydrogen peroxide and molecular oxygen as green oxidants; (4) to assess reusability and stability over five successive cycles and evaluate leaching by inductively coupled plasma mass spectrometry (ICP-MS); (5) to elucidate reaction mechanisms via kinetic studies, in situ spectroscopic monitoring, and density functional theory (DFT) calculations to rationalize activity trends; and (6) to develop a process model for scalable synthesis and integrate life cycle assessment (LCA) to compare environmental impacts with conventional metal-catalyzed systems. A quasi-experimental design is employed, using three bio-based catalyst variants with replicate runs (n=6 per reaction) across a matrix of substrates (10 primary alcohols, 6 secondary alcohols, 4 alkyl halides) and operating conditions (temperature 25–60°C, solvent-free or aqueous media, oxidant stoichiometry 1–3 equivalents). Population-level data are drawn from catalytic performance metrics, including turnover frequency (TOF), turnover number (TON), selectivity, carbon balance, and catalyst leaching. Data collection instruments include gas chromatographs with flame ionization detection (GC-FID), gas chromatography–mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC), Fourier-transform infrared spectroscopy (FTIR) for in situ monitoring, and ICP-MS for metal leaching. Validity and reliability are addressed through calibration curves, method blank controls, and repeatability analysis with relative standard deviations below 5% for key metrics. Statistical analysis comprises analysis of variance (ANOVA) to compare catalytic performance across catalyst types and substrates, followed by Tukey’s HSD post hoc tests; non-linear regression is used to fit kinetic models to rate data, and Langmuir–Hinshelwood or Eley–Rideal mechanisms are evaluated against experimental rate laws. Mechanistic insights are corroborated by DFT calculations at the B3LYP-D3/def2-TZVP level for model fragments to determine energy barriers and favored pathways. The study is grounded in the theories of green chemistry and heterogeneous catalysis, including the principles of atom economy, catalysis by design, and enzyme-inspired active site engineering. Expected findings include (i) demonstration that bio-based catalysts can achieve competitive TOFs (10–200 h?1) with high selectivity (80–98%) for targeted oxidations under solvent-free or aqueous conditions, (ii) robust reusability with negligible metal leaching (<0.1 wt%), and (iii) mechanistic rationalization of activity trends with distinct involvement of Fe–oxo and Cu–oxo centers in concert with biopolymer matrices. The contribution to knowledge lies in establishing a practical framework for designing renewable, non-precious metal catalysts that combine biopolymer supports with tailored active sites to deliver green oxidation performance comparable to traditional noble-metal systems, while enabling easier downstream processing and lifecycle sustainability. The study concludes that carefully engineered bio-based catalysts can provide scalable, environmentally benign alternatives for oxidations, and recommends advancing pilot-scale syntheses, integrating continuous-flow reactor testing, extending the catalyst scope to biomass-derived substrates, and refining LCA models to capture end-of-life scenarios and biopolymer sourcing implications.