Roles of Ru Loading in Modulating Soot Oxidation Activity and Sulfur Resistance of Ru/Al2O3 Catalysts

Ru loading affects both the activity and sulfur resistance of supported Ru catalysts, but the corresponding influencing mechanisms remain unclear. In this study, Ru/Al2O3 catalysts with actual Ru loadings of 0.08–3.77 wt% were prepared and subjected to sulfur poisoning at 350 °C. With increasing Ru loading, the arithmetic mean RuO2 particle diameter grows from 12 to 38 nm, accompanied by a decrease in Ru dispersion. Under loose contact in 10% O2/N2, the fresh catalysts exhibit a volcano-shaped dependence of soot oxidation activity on Ru loading, with 1.91RuAl showing the lowest T50 of 459 °C. Isothermal measurements show that the apparent turnover frequency decreases monotonically at higher Ru loadings, suggesting a balance between the number of accessible Ru sites and their average activity. After sulfur poisoning, the activity increases monotonically with Ru loading, while the change in T50 decreases from +28 to −3 °C. The sulfur content approaches a plateau of approximately 2 wt%, accompanied by a decreasing S/Ru mass ratio. H2-TPR results indicate interactions between Ru species and deposited aluminum sulfate. These findings suggest that Ru loading modifies the balance between sulfate coverage and the promoting effect of adjacent sulfate species. Optimizing Ru loading therefore requires consideration of both fresh soot oxidation activity and the response to sulfur deposition.