Nanozeolite Encapsulated Single-Atom Catalysts: Synergetic In-Situ Conversion of Oil Shale Using Supercritical CO2

Summary The fabrication of a novel NiOx/HY catalyst was carried out for oil shale in-situ conversion, which displayed a favorable catalytic performance under the supercritical carbon dioxide (CO2) atmosphere. Results demonstrate the catalyst with the size of 50 nm can be fabricated by regulating the reaction and crystallization time, the lattice spacing of NiOx/HY expands from about 0.60 nm to 0.72 nm after introducing nickel (Ni), and the pyrolysis temperature of oil shale reduced from 428°C to approximately 360°C by the treatment of NiOx/HY catalyst. The pyrolysis energy barrier was reflected by the activation energy, which dropped from 121.81 kJ/mol to 99.46 kJ/mol. The yields of shale oil and light gas were 12.24% and 55.10% in the nitrogen gas (N2) atmosphere at a temperature of 400°C, which sharply climbed to 37.25% and 23.52% after catalysis treatment in CO2 at a temperature of 400°C. The prepared catalyst combined with supercritical CO2 presented in this study achieves the equivalent hydrocarbon yield at 400°C within 10 hours compared with that at 500°C without catalyst treatment; the required heating temperature can be reduced by 100°C. The technology in this work exhibits excellent performance compared with existing in-situ conversion technologies. The adsorption configurations of the produced hydrocarbons were explored using the molecular dynamics simulations, where the first density peaks of methane (CH4), C2H6, C2H4, and C3H8 would experience a slight decrease in CO2 atmosphere, while the first density peak of the hydrocarbons (C ≥ 4) would increase. Additionally, the interaction energy of hydrocarbon molecules in the CO2 atmosphere is lower than that in the N2 atmosphere due to the replacement of CO2 molecules. Finally, more confined oil and free oil can be detected under a supercritical CO2 atmosphere compared with that in the N2 atmosphere.