A Rational Comparison of the Optimal Promoter Edge Decoration of HDT NiMoS vs CoMoS Catalysts

Abstract : In order to gain a better understanding of the morphology and promoter edge content of the active phase of industrial HDT NiMoP catalysts in working conditions, a multi-technique study has been undertaken on a series of NiMoP catalysts with various Ni/Mo ratios. The combination of X-ray Photoelectron Spectroscopy (XPS), Transition Electron Microscopy (TEM), Density Functional Theory (DFT) modeling and catalytic testing (toluene hydrogenation) provided data to build a morphological model of NiMoS nanocrystallites. A parallel has been established with their CoMoS counterparts obtained in our previous work in order to emphasize differences arising from the promoter atom. This study confirms the importance of the presence of mixed Ni-Mo sites on the edges of the NiMoS nanocrystallites, and especially on the M-edge for reactions involving hydrogenation. These results provide new guidelines for future and ever more active catalysts.