Highly Cr-Substituted CeO₂Nanoparticles Synthesized Using a Non-equilibrium Supercritical Hydrothermal Process: High Oxygen Storage Capacity Materials Designed for a Low-Temperature Bitumen Upgrading Process

As described herein, the synthesis of highly Cr-substituted CeO2 nanoparticles (Cr-CeO2) for low-temperature bitumen upgrading is demonstrated using a supercritical hydrothermal method including a subcritical region. A continuous flow reactor that can provide a non-equilibrium process was used to improve Cr substitution in the CeO2 lattice. Consequently, a Cr-substitution concentration of 22.7 mol %, which was unobtainable using the equilibrium process (5.1 mol %), was achieved. As the Cr-substitution concentration increased, the Cr-CeO2 morphology changed from a perfect octahedron to a cluster of small nanoparticles with high lattice strain. The increase in lattice strain strongly affects the rise in the oxygen storage capacity (OSC) of Cr-CeO2. Results show that high conversion of asphaltene (up to 47.9% at 350 °C) and high selectivity of syngas (H2 and CO, up to 58.3% at 350 °C) were achieved through low-temperature catalytic bitumen upgrading in the presence of highly Cr-substituted CeO2 nanoparticles. Furthermore, results show that the asphaltene conversion increased because of the rise in the OSC of Cr-CeO2, irrespective of the increase in the specific surface area, which indicates that the catalytic potential of Cr-CeO2 is more dependent on OSC than their specific surface area.