Enhanced Pyrolysis of Low to Medium Maturity Oil Shale with Lanthanide and Nitrogen Co-doped Carbon Quantum Dot Catalysts: Mechanistic Insights and Kinetic Implications

Abstract

China’s abundant shale resources include a substantial proportion of low to medium maturity shales, which present significant extraction challenges due to high heating costs, slow pyrolysis rates, and low catalytic efficiencies. To address these issues, this study synthesizes a series of Ln-N/CQDs through a combustion method, including La/N-CQDs, Ce/N-CQDs, and Pr/N-CQDs. Kinetic analysis indicates that the addition of these catalysts reduces the average apparent activation energy required for oil shale pyrolysis. The activation energy decreases from 207.01 kJ/mol to 147.33, 172.78, and 144.94 kJ/mol, respectively. This reduction significantly enhances the pyrolytic capabilities of the organic matter within the shale. Employing molecular dynamics simulation and DFT calculations, the study investigates the impact of Ln-N/CQDs on the pyrolysis behavior of organic matter in oil shales and elucidates the catalytic mechanism. The research finds that electronic perturbations from lanthanide and adjacent heteroatom sites (C and N) alter electronic distribution, inducing charge redistribution. This facilitates efficient electron transfer from the catalyst to the reactive sites of organic molecules in the shale, forming reactive intermediates such as carbon cations. This process significantly lowers reaction barriers, alters pathways, and enhances catalytic efficiency. Overall, this study provides new insights and methodologies to improve the utilization efficiency of low to medium maturity oil shales, paving the way for the development of more effective extraction technologies.