Characterization of carbon- and alumina-supported NiW and CoW sulfided catalysts

Sulfided NiW and CoW catalysts supported on activated carbon and alumina were characterized with Co-57 Mossbauer emission spectroscopy (MES) and EXAFS at the W-L-III edge. NiW catalysts were studied with MES by probing the Ni atoms with 57Co. MES results demonstrate that the 'Ni-W-S' phase is present in sulfided NiW catalysts. Formation of Co9S8-type phases could be related to the lower thiophene HDS activity of CoW catalysts. WEXAFS showed that addition of Co or Ni to a W/Al2O3 catalyst results in a higher W sulfidation degree. No structural differences were found for carbon- and alumina-supported catalysts, in spite of the two times larger thiophene HDS activity of carbon- supported NiW

[Soil-physical, soil-chemical, pedological and general descriptions of some thermally and biologically cleaned soils. Part II. Data and methods.]

Abstract niet beschikbaarThis report describes the sampling methods, the fysico-chemical methods for analysis and the raw data of the soil-physical, soil chemical and several soil-descriptive research as part of a research-program "Ecological recovery of cleaned soils", carried out by the centre of environmental Science (Leiden University) and the National Institute of Public Health and Environmental Protection in the Netherlands.Speerpuntprogramma Bodemonderzoek (PCBB

The effect of support interaction on the sulfidability of Al2O3- and TiO2-supported CoW and NiW hydrodesulfurization catalysts

The effect of the degree of W sulfidation on dispersion, morphology, thiophene hydrodesulfurization (HDS) activity, and promotional behavior for supported Ni(Co)W sulfide catalysts was studied by varying the calcination temperature, sulfidation temperature, sulfidatian pressure, and support. The catalysts were characterized by thiophene HDS, X-ray photoelectron spectroscopy; transmission electron microscopy, extended X-ray absorption fine-structure, and Mossbauer emission measurements. Assuming that sulfidation to a WS2 phase proceeds via a WOxSy phase it can be concluded that the ratio between these two phases depends on the sulfidation conditions and W-support interaction. For the highest thiophene HDS activity, sulfidation conditions that result in nearly maximum sulfidation of the WOxSy phase are necessary. However, one should be aware that complete sulfidation results in the formation of WS2, which is more susceptible to sintering. For Al2O3-supported NiW catalysts preferable sulfidation conditions are a low temperature and a high H2S/H-2 sulfidation pressure. In contrast, for TiO2-supported NiW the calcination and sulfidation temperatures have to be low and sulfidation at atmospheric H2S/H-2 pressure is already sufficient, because W is more easily sulfided due to its weak interaction with TiO2. The degree of sulfidation also affects the promotional behavior. The optimal Ni/W ratio is higher than the optimal Ni/Mo ratio, while in contrast to CoMo catalysts, for CoW no optimal ratio could be found. In addition, the activity of CoW appeared about the same as the sum of the W and Co activities, regardless of the Co content. In the case of NiW and CoW, Ni and Co are sulfided first. As soon as WS2 appears, the NiS particles already formed partially redisperse to form NiWS, while the CoS particles tend to form a separate Co9S8 phase instead of CoWS. (C) 2001 Academic Press

Ni-sulfide particles in NaY-zeolite for combined hydrodesulfurization and hydrocracking purposes, Hyperfine Interactions

The influence of physisorbed water on the formation of nickel- sulfide species in a Co-57 doped ion exchange type Co-57:NiNaY catalyst is studied by Mossbauer Emission Spectroscopy. The absence or presence of physisorbed water during sulfidation seems to have no influence on the local nickel environment of the formed Ni-sulfide species. This result is confirmed by EXAFS measurements. In spite of the resemblance found in MES and EXAFS a large difference is found for the initial HDS activities, which is explained by the different particle sizes (HREM) found at the outer surface of the zeolit

The effect of support interaction on the sulfidability of Al2O3- and TiO2-supported CoW and NiW hydrodesulfurization catalysts

The effect of the degree of W sulfidation on dispersion, morphology, thiophene hydrodesulfurization (HDS) activity, and promotional behavior for supported Ni(Co)W sulfide catalysts was studied by varying the calcination temperature, sulfidation temperature, sulfidation pressure, and support. The catalysts were characterized by thiophene HDS, X-ray photoelectron spectroscopy; transmission electron microscopy, extended X-ray absorption fine-structure, and Mössbauer emission measurements. Assuming that sulfidation to a WS2 phase proceeds via a WOxSy phase it can be concluded that the ratio between these two phases depends on the sulfidation conditions and W–support interaction. For the highest thiophene HDS activity, sulfidation conditions that result in nearly maximum sulfidation of the WOxSy phase are necessary. However, one should be aware that complete sulfidation results in the formation of WS2, which is more susceptible to sintering. For Al2O3-supported NiW catalysts preferable sulfidation conditions are a low temperature and a high H2S/H2 sulfidation pressure. In contrast, for TiO2-supported NiW the calcination and sulfidation temperatures have to be low and sulfidation at atmospheric H2S/H2 pressure is already sufficient, because W is more easily sulfided due to its weak interaction with TiO2. The degree of sulfidation also affects the promotional behavior. The optimal Ni/W ratio is higher than the optimal Ni/Mo ratio, while in contrast to CoMo catalysts, for CoW no optimal ratio could be found. In addition, the activity of CoW appeared about the same as the sum of the W and Co activities, regardless of the Co content. In the case of NiW and CoW, Ni and Co are sulfided first. As soon as WS2 appears, the NiS particles already formed partially redisperse to form NiWS, while the CoS particles tend to form a separate Co9S8 phase instead of CoWS