Changes in metal-sulfur bond energy in promoted and unpromoted molybdenum catalysts

Insight into the changes in the metal–sulfur bond energy in unpromoted and promoted (Co, Ni, or Fe) MoS2 catalysts is obtained by temperature‐programmed reduction (TPR) studies of in situ sulfided catalysts. The experiments reveal a significant decrease in the metal–sulfur bond energy for the more active Co–Mo–S and Ni–Mo–S structures as compared to MoS2. A similar decrease is not observed for the less active Fe–Mo–S structure. The sulfur coordination is directly measured by in situ EXAFS and the results support that one of the roles of the promoter atoms is to facilitate vacancy formation. The findings are in accord with recent density functional theory calculations.