van der Am Kraan

The influence of phosphorus on the structure and hydrodesulfurization activity of sulfided Co and Co-Mo catalysts supported on carbon and alumina

The thiophene HDS activities of phosphorus-containing Co and CozMo sulfide catalysts supported on γ-Al2O3 and activated carbon were measured at atmospheric pressure. Phosphorus decreased the thiophene HDS activity of the carbon-supported catalysts considerably but did not affect the activity of the alumina-supported catalysts. From XPS it was inferred that phosphorus improves the dispersion of the cobalt phase in the oxidic precursor state of both the carbon- and alumina-supported catalysts. In the sulfided state the interaction between phosphorus and the metal sulfide phase appeared to depend on the support. In the sulfided carbon-supported catalysts, phosphorus formed a Co-phosphate phase, which is responsible for the decrease in HDS activity, while on alumina phosphorus did not influence the structure of the metal sulfide phase.

On the so-called "Co-Mo-S" phase observed in carbon-supported cobalt sulfide catalysts : temperature dependence of the in-situ Mössbauer emission spectrum

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Mössbauer emission study on 57Co doped carbon-supported Ni and Ni-Mo sulfide hydrotreating catalysts : the influence of phosphorus on the structure

Abstract In the present study it is demonstrated that Mossbauer emission spectroscopy (MES) can generate information on the various Ni phases present in sulfided Ni containing catalysts when a small amount of 57 Co is used as a probe for Ni. Application of MES to 57 Co:Ni(4.5)Mo(8.0)/C and 57 Co:Ni(5.6)/C revealed the formation of a so-called “Ni-Mo-S” phase in the former and a bulk sulfide in the latter catalyst. After addition of phosphorus a “Ni-(thio)phosphate” phase is found to be formed in both catalysts. The relation between the structure of these catalysts and their activity for thiophene HDS and quinoline HDN is discussed.

The influence of phosphorus on the structure and hydrodesulfurization activity of sulfided Fe and Fe-Mo catalysts supported on carbon and alumina

Phosphorus-containing Fe and Fe−Mo sulfide catalysts supported on γ-Al2O3 and activated carbon were evaluated for their thiophene HDS activities at atmospheric pressure. The thiophene HDS activity of the carbon-supported catalysts decreased considerably in the presence of phosphorus, while the activity of the alumina-supported catalysts was not affected. It was shown by Mössbauer spectroscopy that in both the oxidic carbon- and alumina-supported catalyst precursors the presence of phosphorus resulted in an improved dispersion of the Fe phase. In the sulfided carbon-supported Fe and Fe−Mo catalysts, the presence of phosphorus resulted in the formation of an “Fe(II)-phosphate” phase, which was held responsible for the decrease in HDS activity. With regard to the sulfided alumina-supported catalysts, it was found that phosphorus did not influence the structure of the metal sulfide species.

Iron sulphide containing hydrodesulphurization catalysts: Mössbauer study of the sulphidibility of α-iron(III) oxide

As a first step in the study of the sulphidation of carbon-supported iron oxide catalyst systems the sulphiding of a well-characterized. unsupported model compound. viz. a-Fe,O,, (mean particle diameter ca. 50 nm) was investigated using in-situ M6ssbauer spectroscopy and the temperatureprogrammed sulphiding technique. Sulphidation was carried out in a flow of 10% hydrogen sulphide in hydrogen. At room temperature and atmospheric pressure no bulk sulphidation of the cyFe20,1 particles was observed. However, as the sulphidation temperature increased a direct transformation of bulk a-Fe,O,, into iron sulphides took place. The iron-to-sulphur ratio of the iron sulphides formed during the sulphidation process was initially 2 and decreased to 1 with increasing sulphidation time and/or temperature.

Similarity of Co-species in Co and Co-Mo-sulfide catalysts supported on carbon and alumina : Moessbauer emission spectroscopic study

It is shown that, irrespective of the application of carbon or alumina as a support, the local structure of the “Co-sulfide” phase formed during sulfidation of Co-and CoMo-catalysts is the same. A relation is found between the quadrupole splitting (Q.S. value) of the “Co-sulfide” phase and its dispersion. The higher the dispersion, the larger the Q.S. value. The so-called “Co-Mo-S” doublet is observed in all cases and it turns out to be related to a highly dispersed “Co-sulfide” phase instead of a Co, Mo and S containing phase.

Sulfidation of carbon-supported iron oxide catalysts

The sulfidation of carbon-supported iron oxide catalysts was studied by means of in-situ Mossbauer spectroscopy at temperatures down to 4.2 K. The catalysts were dried in two different ways and then sulfided in a flow of 10% H2S in H2 at temperatures between 293 and 773 K. Thiophene hydrodesulfurization (HDS) activity measurements were performed at 673 K in a flow microreactor operating at atmospheric pressure. The iron content varied from 1.1 to 9.0 wt.-% Fe. In the oxidic catalyst precursors, dried in air at 293 K, nitrate anions were still present. These anions could be removed by means of an additional H2 treatment up to 393 K. This treatment also led to an increase in the interaction strength between the iron (III) oxide particles and the carbon support. It is shown that the transition from iron (III) oxide to iron sulfide proceeded through two intermediate phases, viz. an oxidic high-spin Fe2+-phase and FeS2. A correlation between the HDS activity per mole of iron and the mean iron sulfide particle size was observed, with the mean particle size being dependent on the preparational treatments of the oxidic catalyst precursors.

Sulfidation and activity of Co/C catalysts having extremely low cobalt-loading: A Moessbauer emission spectroscopy and thiophene hydrodesulfurization study

Abstract Up to a sulfidation temperature of 473 K, the behaviour of Co/C catalysts with extremely low cobalt-loadings (ppm range) agrees with the trend observed before in the Mossbauer emission spectroscopy (MES) spectra of Co/C catalysts with much higher cobalt-loadings (0.04–4.3 wt.-%). Interestingly, sulfidation at 573 K results in a rather well-defined very highly dispersed (most likely monatomically) ‘Co-sulfide’ species which shows a doublet with the extremely large value Q.S. = 4.11 m/ms . In this species the cobalt atoms may be four-fold (square-planar) or five-fold (square-pyramid) coordinated by sulfur. Sulfidation at 673 K results in the disappearance of this highly dispersed “Co-sulfide” species and the newly formed species are again similar to the one previously found for Co/C catalysts with higher cobalt-loadings. It is worth noting that this finally formed ‘Co-sulfide’ species does not exhibit the “Co-Mo-S” MES spectrum (Q.S. between 1.0 and 1.3 m/ms ) whereas its intrinsic thiophene hydrodesulfurization (HDS) activity equals that of cobalt in the “Co-Mo-S” phase. These observations clearly lead to the conclusion that there is no general relation between the thiophene HDS activity (measured at atmospheric pressure) and the amount of cobalt exhibiting a “Co-Mo-S” MES spectrum.

Some aspects of the stability of the so-called "Co-Mo-S" phase present in sulfided carbon-supported Co and CoMo catalysts : a Mössbauer emission spectroscopic study

A relation between the quadrupole splitting (Q.S. value) of the “Co-sulfide” phase and its sensitivity to exposure to ambient air could be established by means of Mössbauer emission spectroscopy (MES). For both Co/C and CoMo/C catalysts showing a quadrupole doublet with a large Q.S. value (1.20–1.30 mm/s) air exposure at room temperature for one day did not cause significant changes in the MES spectrum. In the case of catalysts showing a doublet with a smaller Q.S. value, exposure to ambient air resulted in the presence of a high-spin 2+doublet. In addition, for these catalysts air contact is found to give rise to an increase of the Q.S. value of the “Co-sulfide” phase which points to an increased dispersion of the “Co-sulfide” phase.

Stability of the so-called "Co-Mo-S" phase in a carbon-supported Co-Mo sulfide catalyst at very low Co/Mo ratio

Several aspects of the stability of the so-called “Co−Mo−S” phase in a fully sulfided Co(0.04)Mo(6.84)/C (wt%) catalyst have been examined by Mössbauer emission spectroscopy. The “Co−Mo−S” parameters turned out to be unchanged when the catalyst is exposed for 23 days to ambient air at room temperature. However, if this exposure to air is extended for over 100 days, the so-called “Co−Mo−S” phase was found to be oxidized to a high-spin Fe2+ phase which has no strong interaction with the “MoS2” particles. After resulfidation of the catalyst the so-called “Co−Mo−S” phase is formed again.