Enhancing oil shale pyrolysis using metal-doped carbon quantum dot catalysts: A comprehensive behavioral, kinetic, and mechanistic analysis

Abstract

Current oil shale extraction technologies face significant challenges, including high heating costs, slow pyrolysis reaction rates, and low efficiency, which hinder effective resource exploitation. To address these issues, this study synthesized three types of metal-doped carbon quantum dot (M/CQD) catalysts—Co/CQDs, Ni/CQDs, and Mn/CQDs—and tested their effects on the pyrolysis of oil shale. The introduction of these catalysts resulted in a notable enhancement of the pyrolysis process, reducing the required activation energy by approximately 40 % and lowering the initiation temperatures for Co/CQDs, Ni/CQDs, and Mn/CQDs by 64 °C, 62 °C, and 94 °C, respectively. Consequently, the yield of shale oil increased significantly by 23.1 %, 13.3 %, and 19.8 % for each catalyst. Kinetic and product analyses indicate that these catalysts facilitate electron transfer from organic molecules, promoting the formation of free radicals and the cleavage of C–C bonds. This enhancement leads to an increased production of short-chain hydrocarbons and a reduction in oxygenates and esters, thereby improving the quality of the shale oil. Further insights from Density Functional Theory (DFT) calculations suggest that the catalysts enhance pyrolysis by promoting the formation of carbocations and synergizing with radicals released from the shale, intensifying the pyrolysis process. This study not only elucidates the catalytic mechanisms that enhance oil shale pyrolysis but also offers a promising approach to overcome technological challenges in shale resource recovery, such as high heating costs and low efficiency, paving the way for more efficient and cleaner shale oil production.