Mechanism of hydrogen production through lignin supercritical water gasification catalyzed by carbon-supported nickel-based catalyst: ReaxFF molecular dynamics simulation

This work studied the different simulation parameters of lignin in supercritical water gasification (SCWG) reaction and the synergistic catalytic mechanism between Ni atom and carbon carrier for lignin SCWG was explored using the ReaxFF molecular dynamics (MD) method. The effects of different carbon carriers (CNT, graphite, and CNF), lignin mass concentration (10, 12, and 15 wt%), and Ni loading concentration (0, 2.5, 5, 7.5, and 10 wt%) on the distribution of SCWG gas products are considered. Compared to other carbon carriers, CNT has the highest specific surface area, hence Ni/CNT exhibits the strongest hydrogen production catalytic activity. The most favorable parameters for lignin gasification are 2.5 wt% Ni loading concentration and 10 wt% lignin mass concentration. The addition of Ni-based catalysts promotes the cracking of lignin model compound. Ni atoms accelerate the breaking of C-C bonds and disrupt the conjugated π bonds of aromatic rings. The carbon carrier plays a synergistic catalytic role, promoting the reaction towards the direction of "lignin decomposition to generate small molecules". This study provides in-depth research on the product distribution and the catalytic mechanism of carbon-supported nickel-based catalysts, which is expected to provide theoretical guidance for improving the SCWG efficiency of lignin.