Co-AC catalyst

Recent work done by Xiong et al.84 on Co/AC (activated carbon) catalysts showed that a Co2C species formed during the catalyst reduction in hydrogen at 500°C. Evidence for the carbide in the Co/AC catalysts was obtained by x-ray diffraction and XPS measurements, and the formation of this Co2C species reduced the FTS activity over the Co-based catalysts. The presence of bulk carbide also seems to enhance alcohol selectivity.85... 

In hydrocracking of HVGO alone the reason for decreased gas formation over Co-AC catalyst (compared with a thermal run) may be the fact that the activated carbon leads to the formation of more H or HS which terminates the radical degradation pathy-ways. However, in the case of a blend, in the absence of catalytic activity, hydrocarbon quenching (with radicals from derivated plastics) may be more pronounced than hydrogen quenching (with H ). 

For the Co/AC catalyst sulfided at 373 K, van der Kraan et al. observed the MOS doublet that coincided with the Co-Mo-S doublet in the CoMo/AC catalyst. However, after sulfiding of the Co/AC at 673 K, the doublet disappeared. At the same time, in CoMo/AC catalyst sulfided at 673 K the Co-Mo-S doublet was present, although slightly changed. In spite of the doublet similarities, the activity of the Co/AC sulfided at 373 K for H2—D2 exchange was much lower than that of the CoMo/AC catalyst sulfided at 673 K. It is believed that the higher activity must result from the presence of the Co-Mo-S active phase. Therefore, the doublet in the Co/AC sulfided at 373 K may be attributed to some unidentified phase. 

When combined with AC, the Co/AC catalyst was more active for HDS of thiophene than the Mo/AC catalyst. According to the results in Figure 37, the rate constant for HDS increased up to about 7wt.% metal loading. The subsequent HYD of butenes, produced during the HDS of thiophene, to butane was more pronounced over the Co/AC catalyst as well. The experiments were conducted in an autoclave at 673 K and a near atmospheric pressure of H2. Under these conditions, the Co/AC catalyst was much more active than the commercial C0M0/AI2O3 catalyst. 

Ni-W-S phase in the NiW/AC catalysts. In this case, the WS2 particle growth in the c direction was observed on the addition of Ni. The NiW/AC catalyst was more active than the CoW/AC catalyst. Although Co-Mo-S phase was detected, this catalyst was prone to the formation of CogSg. For the same amounts of active metals, presence of the Ni-W-S phase in the NiW/AC catalyst was more evident than the Co-W-S phase in the CoW/AC catalyst. A similar observation was also made for the CoMo/AC catalyst. ... 

It was noted earlier that depending on sulfiding temperature, Type-I and Type-II Co-Mo-S active phases can be formed in the y-Al203-supported catalysts. For the latter formed at higher sulfiding temperatures, the interaction with y-Al203 was not evident. On the basis of MOS results, Topsoe concluded that the active Co-Mo-S phase in the CoMo/AC catalyst resembled Type-II phase in the y-Al203-supported catalysts. It appears that such a phase is facilitated when the interaction with catalyst support is minimal. 

Figure 37 Effect of metal loading on the HDS rate constant for Co/AC and Mo/AC catalysts.

The active-metal combinations such as Co Ni, Co-Mo and Ni-Mo supported on AC exhibited a high activity during upgrading of the feed obtained from scrap tires by pyrolysis. The experiments were conducted at 573, 623 and 673 K at 7 MPa of H2. The yields of naphtha and kerosene fractions, as well as the rate of HDS were the parameters used to estimate the activity. In this regard, the NiMo/AC catalyst was the most active, although the activity difference among the three catalysts was not so large. 

The noble-metal (Pt, Pd. Ru and Rh) sulfides in combination with Mo, supported on AC exhibited higher activity for HYD of carbonyl and carboxylic groups than Mo/AC catalyst alone. They also accelerated hydrogenolysis of the etheric bonds such as CH3 O and Car-0. However, bimetallic catalysts without Co had no activity for decarboxylation. The H2S/H2 ratio had a different effect for every noble metal. In this study, GUA, 4-MA, ED, 4-methyl phenol and 2-octanone were used as model compounds. Thus study was conducted in an autoclave at 553 K and 7 MPa of H2. 

Lee et used the ebullated-bed reactor for catalyst preparation from AC and soluble metal precursors. In their study, the oil-soluble Mo and Co naphthenates were introduced with an AR into the continuous ebullated bed of AC granules (623 K and 6.9 MPa of H2). The co-dispersed catalyst exhibited high activity for HDS, HDM and HDAs at the optimal Co/(Co + Mo) ratio of 0.3. However, the HCR activity of the Mo/AC catalyst was greater than that of the CoMo/AC catalyst. 

For example, for NiW/AC catalysts, the combinations comprised 0.1 to 15 wt.% of Ni, 1 to 50 wt.% of W. The catalysts exhibited high activity for simultaneous HDAr, HDN and HDS. Another catalyst formulation disclosed by Sudhakar comprised a sulfided catalyst consisting of zinc, one or more non-noble metals selected from Ni, Co and Fe and either Mo or W supported on AC. Under typical hydroprocessing conditions these catalysts exhibited high activities for HYD, HDAr, HDS and HDN. 

The addition of other metals to the heterogeneously cobalt-catalyzed reaction can have a beneficial effect on hydroformylation. For example, small amounts of ruthenium added to a carbon-supported cobalt catalyst (Co/AC) increased activity as well as Hb selectivity [64]. The effect was rationalized by the high dispersion and reducibUity of supported cobalt. When ruthenium was added, small particles of an unbalanced alloy were formed. These particles keep more CO in a nondisso-ciative state and lower the surface hydrogen pressure. This was in contrast to the related but uniformly distributed Pt-Co or Pd-Co alloys. Activity and regioselectivity increased with increased Ru loading. 

For the Ru-Ba/AC catalyst prepared by RuCls acetone solution and aqueous solution, washing process affects the adsorption capacity of H2 and CO and the grain size of ruthenium.The samples washed by ammonia have obviously larger adsorption capacity compared with the untreated samples. This shows that the ammonia washing can remove the residual chlorines. 

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