Nature of the different nickel species in sulfided bulk and alumina-supported nickel-molybdenum hydrotreating catalysts

Abstract

Bulk nickel molybdenum sulfides have been studied by X-ray photoelectron spectroscopy (XPS) and compared to a sulfided / -1203 catalyst. Several types of Ni species have been identified on both catalytic systems. A particular Ni species has been observed and assigned to Ni located at the edges of the MoS2 slabs in a decoration position forming the so-called NiMoS phase. In bulk nickel molybdenum sulfides, ion scattering spectroscopy (ISS) and XPS results show that, for an atomic ratio Ni/(Ni + Mo) between 0.2 and 0.8, a particular surface composition exists, resulting from the existence of a phase of composition Ni/(Ni + Mo) between 0.2 and 0.3 and identified as the "NiMoS" phase. A comparison with the Ni-W system shows that the Ni species in decoration position is present in both the Moand W-based catalysts and can be assumed to be responsible for the synergy effect observed in these catalysts. On alumina, existence of this NiMoS phase has been found to be dependent on the sulfidation temperature of the oxide precursor.

A DFT Study of CoMoS and NiMoS Catalysts: from Nano-Crystallite Morphology to Selective Hydrodesulfurization

“…In contrast, the model, corresponding to higher p(H 2 S)/p(H 2 ), maximizes the promoter content (Ni/Mo ratio of 0.40) and minimizes the number of mixed sites. According to the usual Ni/Mo ratio (smaller than 0.40) observed by XPS and required for best HDS activities [8,9], the working crystallites must combine edge structures allowing the presence of mixed Ni-Mo edge sites. This point will be analyzed in details in the paper by K. Marchand et al published in the present volume [82].…”

“…Up to now, numerous experimental techniques have been employed to better characterize the catalytically "CoMoS" or "NiMoS" active phases [2,3]. Experimental techniques involved in the characterization of these complex phases consist of transition electron microscopy (TEM) [4,5], X-ray photoelectron spectroscopy (XPS) [6][7][8][9], Mössbauer spectroscopy [10][11][12], laser Raman spectroscopy [5,13], extended X-ray absorption fine structure (EXAFS) [14][15][16][17][18], and IR spectroscopy [19,20]. These techniques furnished many detailed features of the so-called Co(Ni)MoS active phase made of MoS 2 layers with a stacking close to 1 [21] and nanometer sizes (less than 30 Å), "decorated" by Co or Ni at the edges.…”

“…These techniques furnished many detailed features of the so-called Co(Ni)MoS active phase made of MoS 2 layers with a stacking close to 1 [21] and nanometer sizes (less than 30 Å), "decorated" by Co or Ni at the edges. While Mössbauer spectroscopy [10][11][12] and XPS [6][7][8][9] revealed the specific signature of Co atoms engaged in the new CoMoS phase, EXAFS gave relevant insights into the local environment of the promoter atoms (Co or Ni) in the structure [14][15][16].…”

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

“…Promotions/decorations and sulfidations of those catalysts may be characterized by X-ray Photoelectron Spectroscopy (XPS). This technique is also appropriate to identify the electronic state of Co species [1][2][3][4] and Ni species [5][6][7] in the active phase and to quantify them [8,9]. More recently, Density Functional Theory (DFT) has also appeared as a very efficient method to bring new insights on the local structure and electronic properties of the active phase of HDT catalysts [10,11].…”

Characterization and hydrodesulfurization activity of CoMo catalysts supported on sol–gel prepared Al2O3

“…The most typical HDS catalysts consist of a MoS 2 active phase promoted by Co or Ni atoms, called 'CoMoS' or 'NiMoS' phase, both of which have been extensively researched [4][5][6][7][8][9], and by porous γ-Al 2 O 3 supports. Noble metals have often been proposed as newly developed active phases.…”