Structure–Activity Correlations in Hydrodesulfurization Reactions over Ni-Promoted Mo_xW_(1–x)S₂/Al₂O₃ Catalysts

Abstract

In this work, we have investigated the activation process and structure of Ni-promoted Mo x W(1–x)S2/Al2O3 hydrodesulfurization (HDS) catalysts. Conversion of Mo and W oxides to the catalytically active MS2 (M = Mo, W) phase by sulfidation in gaseous H2S/H2 proceeded via different pathways, as found by XPS and EXAFS. The slower sulfidation kinetics of W on the alumina support formed NiMo x W(1–x) sulfides with a two-dimensional core–shell structure. Mo was mostly located in the core and W in the shell, as evidenced by EXAFS. Increasing the H2S/H2 pressure during sulfidation distributed Mo and W more homogeneously in the metal sulfide particles. This was attributed to the more favorable sulfidation of W under these conditions (i.e., below the temperature of MoS2 formation). Catalytic testing was consistent with these findings and demonstrated that a core–shell structure is the active phase in thiophene HDS (1 atm), whereas a homogeneously mixed MS2 phase catalyzes the HDS of dibenzothiophene at 40 bar. This is the first example of a core–shell structure in promoted Mo x W(1–x)S2 catalysts. Support interactions in the oxidic precursor, which affect the sulfidation kinetics, were determined to play a key role in the formation of these structures.

Instability of NiMoS2 and CoMoS2 Hydrodesulfurization Catalysts at Ambient Conditions: A Quasi in Situ High-Resolution Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy Study

“…Due to the detrimental effect of ambient air on the slabs, at t=24 h about 450 slabs per sample were left for analysis, while after month in air only around 300 slabs were left for analysis in the same regions of the samples that had been studied before. 19 The respective binding energies of these components are listed in Table 1 and agree well with previously reported studies [20][21][22] . However, solely based on observations of a small number of slabs, no conclusions can be drawn.…”

Improved promoter effect in NiWS catalysts through a molecular approach and an optimized Ni edge decoration

“…Moreover, the mobility of Ni x S y species -the Hüttig temperature[26] of Ni 3 S 2 is about 260°C -enhances the incorporation of Ni in the WS 2 phase being simultaneously formed at lower temperature than through conventional methods. In conventional catalysts, which exhibit no W sulfide phase at 23°C under similar conditions,[2,27] incorporation of Ni in WS 2 slabs is likely delayed, and provides lower promotion levels (%NiWS), in particular for calcined samples [23]. These different genesis processes of NiWS also impact the Ni distribution at the crystallites' edges as it will be discussed with the help of DFT calculations (vide infra).…”

Dendritic micro–mesoporous composites with center-radial pores assembled by TS-1 nanocrystals to enhance hydrodesulfurization activity of dibenzothiophene and 4,6-dimethyldibenzothiophene

“…However, the hydrogenation of the phenyl ring could alleviate the steric hindrance of methyl substitutes at the 4 and 6 positions near to sulfur atom through the conformational change of the planar phenyl ring [15][16][17]. While the most commonly used catalysts for HDS at present in industry are based on alumina supported NiMo or CoMo materials [18][19][20], they fail to meet the latest fuel standards because of their low hydrogenation performance and high metal-support interaction (MSI) [21,22].…”