Comparative Analysis of Catalytic Processes for CO2 Conversion Efficiency

Thesis Abstract

In pursuit of sustainable chemical energy cycles, this study addresses the comparative efficiency of catalytic processes for CO2 conversion under industrially relevant conditions, focusing on the relative performance of heterogeneous oxide catalysts, metal–organic frameworks, and single-atom catalysts in terms of conversion rate, selectivity to target products, energy intensity, and catalyst durability. The aim is to identify how catalyst class, active site design, and reaction environment influence CO2 activation and subsequent conversion pathways, with a view toward scalable integration into existing petrochemical infrastructure. Specific objectives are (i) to benchmark catalytic activity and selectivity for CO2 hydrogenation, CO2 electroreduction, and CO2-rich reforming across representative catalysts; (ii) to quantify activation energies, turnover frequencies, and apparent reaction orders using standardized reactor configurations; (iii) to evaluate catalyst stability and deactivation mechanisms over 100–300 hour stability tests; (iv) to elucidate structure–activity relationships via in situ and operando spectroscopic characterization; and (v) to model process-level implications for energy efficiency and greenhouse gas mitigation. Methodologically, the study employs a mixed-methods design. The population comprises commercially relevant catalyst formulations drawn from three classes metal oxides (e.g., CeO2, TiO2-based systems), metal–organic frameworks (MIL-101 derivatives), and single-atom catalysts (Pt, Cu, or Ni dispersed on nitrogen-doped carbon). A stratified random sampling approach selects 12 catalyst systems (4 per class) with three synthesis batches each, totaling 36 experimental units. Data collection combines quantitative kinetic measurements in microreactor and flow cell setups at 20–200 °C and 1–40 bar, with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray absorption near-edge structure (XANES), and operando Raman spectroscopy to capture active-site evolution and reaction intermediates. Product distributions are quantified by gas chromatography–mass spectrometry (GC-MS) and online mass spectrometry, while energy consumption is tracked through calorimetric and electrical input readings. To complement experimental results, density functional theory (DFT) calculations determine adsorption energies and transition states for representative reaction steps on selected catalyst surfaces, enabling correlation of theoretical barriers with observed activity. Data analysis integrates multiple techniques. Kinetic parameters (turnover frequency, activation energy) are extracted via nonlinear regression based on Langmuir–Hinshelwood and microkinetic models, with model selection guided by Akaike information criterion. Statistical comparisons across catalyst classes utilize analysis of variance (ANOVA) and post hoc Tukey tests to identify significant differences in activity and selectivity. Stability and deactivation data are analyzed with time-to-event modeling and regression to identify dominant mechanisms (coking, sintering, phase transformation). Spectroscopic data are interpreted through multivariate principal component analysis (PCA) and in situ spectral deconvolution to link intermediate species with observed performance. Theoretical results from DFT underpin descriptors such as CO2 adsorption energy, d-band center alignments, and charge transfer indicators, which are integrated with experimental findings via a unified structure–activity–stability framework. Expected findings indicate distinct performance trade-offs among catalyst classes oxide supports may offer robust recyclability but moderate selectivity toward higher-value products; metal–organic frameworks could provide tunable active sites with enhanced CO2 activation yet face stability challenges under harsh conditions; single-atom catalysts are anticipated to deliver superior atom efficiency and selectivity due to isolated active sites, potentially at the cost of higher synthesis complexity and modest turnover numbers. Across all systems, strong correlations are anticipated between activation barriers derived from DFT and experimentally observed rates, with the most favorable catalysts achieving a balance of low activation energy, high turnover frequency, and minimal deactivation over the 200-hour window. The study contributes to knowledge by delivering a comprehensive, cross-class comparison of CO2 conversion catalysts under harmonized conditions, establishing reliable structure–performance–stability relationships, and providing actionable insights for scale-up and process integration in decarbonization strategies. It is expected to inform catalyst design guidelines emphasizing site isolation, support interactions, and operational envelopes that maximize energy efficiency. Recommendations include prioritizing single-atom catalyst platforms with robust stabilization strategies, optimizing framework materials for thermal and chemical resilience, and implementing in situ diagnostic protocols for real-time performance monitoring to support predictive maintenance and process optimization in industrial CO2 conversion units.