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Insight into the formation of the active phases in supported NiW hydrotreating catalysts

“…More complete sulfidation at higher temperature leads to WS 2 slabs allowing the redispersion of Ni sulfide species and the formation of 'Ni-W-S'-type structures as found by several groups [15,[37][38][39][40] and evidenced by 57 Co Mössbauer spectroscopy on 57 Co-doped NiW/Al 2 O 3 [18]. The presence of such analogues of the 'Co-Mo-S' phase has been demonstrated for carbon-, alumina-and silica-aluminasupported NiW catalysts [9,20]. Although similarly a 'Co-W-S'-like phase was identified for carbon-and alumina-supported CoW catalysts [9], it is clear that Co is prone to the formation of Co 9 S 8 and hence the amount of Co ending up in the 'Co-W-S' phase is rather limited.…”

“…The presence of such analogues of the 'Co-Mo-S' phase has been demonstrated for carbon-, alumina-and silica-aluminasupported NiW catalysts [9,20]. Although similarly a 'Co-W-S'-like phase was identified for carbon-and alumina-supported CoW catalysts [9], it is clear that Co is prone to the formation of Co 9 S 8 and hence the amount of Co ending up in the 'Co-W-S' phase is rather limited. The crucial difference with the Nipromoted system appears to be the ability of the nickel sulfide particles to redisperse to smaller, better ordered species in close contact with WS 2 [5,20].…”

“…The crucial difference with the Nipromoted system appears to be the ability of the nickel sulfide particles to redisperse to smaller, better ordered species in close contact with WS 2 [5,20]. The strong difference in the evolution 57 Co Mössbauer emission spectra of sulfided NiW and CoW [9,18] and the earlier work on the probing of Ni in NiMo catalysts by 57 Co [44] indicate that Ni in NiW can be probed by 57 Co Mössbauer emission spectroscopy.…”

“…The active phase of supported NiW sulfide catalysts is thought to be similar to the 'Co(Ni)-Mo-S' phase in Co(Ni)Mo sulfide catalysts and thus to consist of dispersed WS 2 slabs with the promoter ions www.elsevier.com/locate/apcata Applied Catalysis A: General 322 (2007) [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] adsorbed to their edges. Indeed, Mössbauer spectroscopy which has been instrumental in identifying 'Co-Mo-S'-type phases provides clear evidence that analogous ternary phases are present in sulfided NiW catalysts [9]. On the other hand, it is also obvious that there are considerable differences between Mo-and W-based catalysts, the difference in sulfidation behaviour resulting in incompletely sulfided tungsten phases and the influence of Ni and Co promoters to name the most striking ones.…”

Characterization and thiophene hydrodesulfurization activity of amorphous-silica–alumina-supported NiW catalysts

“…This implies a redispersion of the Ni-sulfide phase to smaller, better ordered species [2,12]. We have recently focused on sulfided alumina-and carbon-supported NiW and CoW [12,19] and identified the "Ni-W-S" and "Co-W-S" analogues of "Co-Mo-S"-type phases by 57 Co Mössbauer spectroscopy. Additional indications for the decoration of the WS 2 edges by Ni species was provided by NO FTIR results of Reinhoudt et al [10].…”