Effect of Water on Dibenzothiophene Hydrodesulfurization over La-Promoted CoMo and NiMo Catalysts

This study investigates the impact of water impurities on the performance and stability of lanthanum-promoted CoMoP/Al 2 O 3 -La and NiMoP/Al 2 O 3 -La catalysts. Catalysts were tested in a fixed-bed reactor using a model feedstock with dibenzothiophene, with activity monitored before, during, and after the introduction of a 10 vol % water cofeed. A comprehensive characterization suite (HRTEM, XRD, XPS, SEM-EDX) linked performance to structural properties. It is shown that both catalysts deactivated upon water injections, the CoMoP/Al 2 O 3 -La catalyst suffered a >10-fold increase in the residual sulfur content in the hydrogenated product compared to only a 3-fold increase for the NiMoP/Al 2 O 3 -La catalyst. These results correlate well with activity tests of the catalysts without La. HRTEM data showed that the stacking number of active component particles in the NiMoP/Al 2 O 3 -La catalyst increased slightly, while particle length remained unchanged, whereas the CoMoP/Al 2 O 3 -La catalyst underwent significant reconstruction, its stacking number decreased from 1.8 to 1.5 and its particle length increased from 3.0 to 3.5 nm, indicating disintegration of the sulfide active component particles. XRD data further showed greater hydrothermal alteration of the γ-Al 2 O 3 support lattice in the CoMoP/Al 2 O 3 -La catalyst. This was coupled with extensive migration and aggregation of lanthanum, which was effectively suppressed in the NiMo system, suggesting nickel clusters anchor the promoter and stabilize the support. XPS analysis data showed that the NiMoP/Al 2 O 3 -La catalyst demonstrates fundamentally superior hydrothermal stability due to robust NiMoS phases and a synergistic Ni–La interaction that mitigates water-induced structural degradation.