Elucidating Cobalt Promotion in Supported Re Sulfide Catalysts in HDS/HER

Rhenium sulfide catalysts supported on carbon or alumina and modified with cobalt were investigated to understand the formation of an active sulfide phase and the effect of cobalt. These Co–Re–S materials were evaluated as catalysts for hydrodesulfurization (HDS) and electrocatalytic hydrogen evolution reaction (HER). Operando X-ray absorption spectroscopy (XAS) at the Co K- and Re L-edges, never before applied for these systems, was employed to characterize the Re-based catalysts, while chemometric tools (MCR-ALS) were used to study their sulfidation behavior. The sulfidation of the initial Re oxide species proceeded through an oxysulfidic intermediate, leading to the formation of ReS2 in both sulfidation atmospheres (H2S/N2 or H2S/H2). In contrast, sulfidation of the initial cobalt species gave CoS2 in H2S/N2 and Co9S8 in H2S/H2. However, in the presence of Re, a mixed CoReS phase was formed. The structure of the active CoReS sites was proposed based on a combination of characterization techniques and computational methods, including DFT optimization of mixed metal sulfide structures, XANES simulations, and linear combination fitting. The impact of the activation conditions was also studied, revealing that sulfidation in H2S/N2 produced more active catalysts than sulfidation in H2S/H2, with the formation of ReS2 in both cases. The addition of cobalt to ReS2 significantly enhanced the catalytic activity for both HDS and HER, indicating the formation of highly active CoReS sites.