Supercritical water gasification of naphthalene over iron oxide catalyst: A ReaxFF molecular dynamics study

ReaxFF molecular dynamics simulation has been employed to investigate the iron oxide catalyzed supercritical water gasification (SCWG) of naphthalene (NAP), a common component of refractory polycyclic aromatic hydrocarbons. Simulation results showed that synergistic effects between SCW and iron oxide catalyst enormously promoted the degradation of NAP and the production of H-2 and CO. During the gasification process, SCW served not only as H source for H-2 generation but also as O source for CO generation and lattice oxygen recompense, while the major roles of iron oxide catalyst were to provide lattice oxygen with high hydrogen-abstraction ability, catalyze SCW to produce more active species, and weaken the C-C bonds. The effects of different parameters were subsequently revealed: increasing the use of H2O molecules raised H-2 and CO yields along with the lattice oxygen supplement but slowed the rate of CO generation, high hydrogen recovery was achieved at high NAP concentration accompanied by a low carbon gasification efficiency. Our simulated results further demonstrated that the deactivation of iron oxide catalyst was caused by carbon deposition, lattice oxygen exhaustion and iron loss. SCW media effectively inhibited the iron loss, while calcination in O-2 environment could successfully regenerate the iron oxide catalyst by cleaning up the carbon deposition and replenishing the lattice oxygen. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.