Nature of cobalt species during the in situ sulfurization of Co(Ni)Mo/Al2O3 hydrodesulfurization catalysts.

Mustafa Al Samarai,Dimosthenis Sokaras,Boyang Liu,Tsu-Chien Weng,Marte Van Der Linden,Eelco T C Vogt,Christa H M Van Oversteeg,Ad M J Van Der Eerden,Frank M F De Groot,Mario Ulises Delgado-Jaime,Bert M Weckhuysen

doi:10.1107/s1600577519002546

Abstract

The evolution in local structure and electronic properties of cobalt was investigated during in situ sulfurization. Using a combination of 1s X-ray absorption (XAS) and 1s3p resonant inelastic X-ray scattering (RIXS), the valence, coordination and symmetry of cobalt ions were tracked in two cobalt-promoted molybdenum oxide precursors of the hydrodesulfurization catalyst system, namely Co-Mo/Al2O3 and Co-Ni-Mo/Al2O3. Extended X-ray absorption fine structure shows that the Co-O bonds were replaced with Co-S bonds as a function of reaction temperature. The cobalt K pre-edge intensity shows that the symmetry of cobalt was modified from Co3+ Oh and Co2+ Oh to a Co2+ ion where the inversion symmetry is broken, in agreement with a square-pyramidal site. The 1s3p RIXS data revealed the presence of an intermediate cobalt oxy-sulfide species. This species was not detected from XAS and was determined from the increased information obtained from the 1s3p RIXS data. The cobalt XAS and RIXS data show that nickel has a significant influence on the formation of the cobalt oxy-sulfide intermediate species prior to achieving the fully sulfided state at T > 400°C.

Highlights

The development of novel hydrodesulfurization (HDS) catalysts has been one of the interesting research subjects in the field of heterogeneous catalysis because of the new environmental regulations to reduce sulfur emissions of transportation fuels (Eijsbouts et al, 2008)
We study the valence, coordination and spinstate changes of cobalt in single and double promoted HDS catalysts, using a combination of 1s X-ray absorption (XAS) and 1s3p resonant inelastic X-ray scattering (RIXS)
Before presenting the results of the in situ sulfurization, we briefly discuss the catalytic activity of the Co–Mo–S/Al2O3 controller that regulates the type and amount of gas that and Co–Ni–Mo–S/Al2O3 catalysts towards the thiophene passes through the reactor

Summary

Introduction

The development of novel hydrodesulfurization (HDS) catalysts has been one of the interesting research subjects in the field of heterogeneous catalysis because of the new environmental regulations to reduce sulfur emissions of transportation fuels (Eijsbouts et al, 2008). The catalytic performance of this active phase is determined by the structure of the oxide precursor species, which is strictly dependent on the preparation methods (Topsøe et al, 1984; Kibsgaard et al, 2010). Among the many synthesis steps involved, the sulfurization process is very likely the step that determines the final structure and performance of the active Co–Ni–Mo/Al2O3 catalyst material. Performed detailed density functional theory calculations of the Co–MoSx system (Saricet al., 2017, 2018) They calculated the structures of the edges, basal plane and corners of the MoS2 slabs and found that the HDS activity is related to the small energy differences between structures with or without a sulfur atom for the corners and the S edges, but not the Mo edges

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