Mechanism of sulfur poisoning to Ru-based catalysts in supercritical water gasification of glycerol: From experiment to combined DFT and kinetics studies

Systematic experimental and kinetic studies were carried out to investigate the effect of sulfur toxicity on the performance of Ru-based catalysts in supercritical water gasification of glycerol. The principal display of catalyst sulfur poisoning is a reduction in catalytic activity for the water–gas shift reaction due to the competition of sulfur and CO in the active site. Consequently, CO production rose with increasing sulfur concentration, while H₂ yield gradually decreased. DFT calculations confirmed that the adsorption energy of CO at Ru and Ni surfaces tends to decrease in the presence of surface S, thus promoting CO desorption. A kinetic model involving the adsorption and desorption process was developed based on the proposed reaction network and calculations provide clear evidence for experimental observation that the CO adsorption rate decreases with increasing sulfur concentration, from 9.36 × 10⁻² to 6.24 × 10⁻² L²·mol⁻¹·min⁻¹·g_cat⁻¹, while desorption rate rises, from 5.20 × 10⁻³ to 1.56 × 10⁻¹ L²·mol⁻¹·min⁻¹·g_cat⁻¹.