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

K Marchand,D Guillaume,P Raybaud,C Legens

doi:10.2516/ogst/2009037

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.

Highlights

The production of ever cleaner fuels with ultra low sulfur content requires a continuous improvement of the catalysts used by the refining industry
These calculations have been successfully confronted to experimental results on CoMo catalysts in a previous study [8]: the decomposition of the X-ray Photoelectron Spectroscopy (XPS) spectral envelope was used to quantify the amount of CoMoS phase, determine the promoter-to-molybdenum ratio in the nanocrystallites and normalize the catalytic activity in toluene hydrogenation per edge CoMoS site
We extended that study to NiMo catalysts, exploring the characteristics of the NiMoS active phase by a multitechnique approach combining X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), catalytic tests and Density Functional Theory (DFT) calculations

Summary

Introduction

The production of ever cleaner fuels with ultra low sulfur content requires a continuous improvement of the catalysts used by the refining industry. Schweiger [14] et al put forward two distinct behaviors at the metallic-edge and sulfur-edge with respect to the promoter: they found that Co is more stable in substitution at the S-edge than at the Mo-edge due to a smaller edge energy at the S-edge, which is supported by other DFT simulations [15] and STM experiments on gold supported CoMoS [16] These calculations have been successfully confronted to experimental results on CoMo catalysts in a previous study [8]: the decomposition of the XPS spectral envelope was used to quantify the amount of CoMoS phase, determine the promoter-to-molybdenum ratio in the nanocrystallites and normalize the catalytic activity in toluene hydrogenation per edge CoMoS site. We make a proposal deduced from these techniques for the most coherent model of morphology and active sites of the NiMoS phase and discuss it with respect to the CoMoS phase model recently proposed on the same bases

Objectives

Methods

Results

Discussion

Conclusion