NiFe-LDH enhanced water-steam pyrolysis of kerogen: unveiling steam-catalytic interplay and multi-scale reaction dynamics

Low to medium maturity shale oil, an essential energy source, faces challenges due to traditional pyrolysis methods, which are characterized by high energy consumption, low yield, and poor selectivity. Moreover, the inefficiencies in in-situ heat injection underscore the necessity for effective catalysts and improved heat transfer mechanisms involving water vapor. This study aims to elucidate the heat transfer enhancement and catalytic synergy of NiFe-layered double hydroxides (NiFe-LDH) in improving the in-situ pyrolysis efficiency of medium–low maturity oil shale via steam pyrolysis. Analyses conducted using GC–MS, Raman spectroscopy, and 13 C NMR demonstrated that the incorporation of NiFe-LDH with water vapor significantly enhances kerogen pyrolysis. This process increases the yields of alcohols, alkanes, and olefins by 1.32, 1.21, and 1.81 times, respectively, and it reduces the temperature needed to produce oil from kerogen. The catalyst helps turn aromatics into alcohols, olefins, and alkanes while breaking down residues into short-chain alkanes. It does this by weakening C–H bonds and removing hydrogen from methyl groups, ultimately reducing the energy required for heat injection by 38.17 %. Thermal and kinetic studies reveal that NiFe-LDH increases kerogen thermal diffusivity by 75.5 % and decreases specific heat capacity by 28.1 %, while elucidating the kinetic mechanism for a 59 °C elevation in the initial temperature of the main pyrolysis stage (increasing 6.1 times prefactor). A nucleation-reaction-order-geometric contraction multi-mechanism coupling model is established. This work proposes a novel “catalyst-water vapor pyrolysis-kerogen oxidation” synergistic enhancement theory, refining the multi-scale coupling mechanisms of heat/mass/chemical reactions during in-situ oil shale pyrolysis.