Reaction mechanism and kinetics of kerogen dehydrogenation and cyclization investigated by density functional theory

The efficient utilization of oil shale holds significant potential in addressing the global energy shortage. However, the limitations of existing laboratory equipment capacity have prevented the complex pyrolysis micro-mechanisms of oil shale from being revealed, thus hindering further control and optimization of the pyrolysis process. In this study, the density functional theory was employed to investigate the microscopic mechanism of alkane molecule pyrolysis in oil shale kerogen. The research revealed that the average energy barrier of dehydrogenation reactions is the largest during the pyrolysis process of kerogen. Moreover, even for the same type of chemical bond, energy barriers vary due to the intrinsic nature of the bond. Regarding bond formation during the reaction process, it was found that chemical bonds are not continuously formed during cyclization; instead, a plateau region may occur wherein chemical bonds form rapidly only upon overcoming this plateau region. This study reveals the microscopic mechanism of pyrolysis of alkane molecules in oil shale kerogen molecules, bridging the gap brought about by the limitation of experimental conditions, filling the gaps in experimental mechanism studies and providing new directions for future industrial production of oil shale.