Sulfur Impact on Methane Steam Reforming over the Stoichiometric Natural Gas Three-Way Catalyst

The steam reforming of CH₄ plays a crucial role in the high-temperature activity of natural gas three-way catalysts. Despite existing reports on sulfur inhibition in CH₄ steam reforming, there is a limited understanding of sulfur storage and removal dynamics under various lambda conditions. In this study, we utilize a 4-Mode sulfur testing approach to elucidate the dynamics of sulfur storage and removal and their impact on three-way catalyst performance. We also investigate the influence of sulfur on CH₄ steam reforming by analyzing CH₄ conversions under dithering, rich, and lean reactor conditions. In the 4-Mode sulfur test, saturating the TWC with sulfur at low temperatures emerges as the primary cause of significant three-way catalyst performance degradation. After undergoing a deSOx treatment at 600 °C, NOx conversions were fully restored, while CH₄ conversions did not fully recover. Experimental data under fixed lambda conditions reveal that sulfur stored on the catalyst leads to reduced CH₄ conversions by steam reforming at high temperatures under rich conditions. In contrast, CH₄ conversions by oxidation at high temperatures under lean conditions remain consistent, indicating a greater impact of sulfur on CH₄ steam reforming. Analysis using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows the potential for sulfur-induced deterioration of active sites and oxygen storage capacity, resulting in the formation of carbonaceous species on the catalyst surface.