Cobalt oxide-supported metal catalysts

With supported metal catalysts that have to be treated in a reducing gas flow at elevated temperatures to convert the catalytic precursor into the desired metal, it is important to assess the extent of reduction. Often the oxidic phase of the cata-lytically active precursor is stabilized by interaction with the support. It is even possible for a finely divided precursor to react with the support to a compound much more stable than the corresponding metal oxide. An example is cobalt oxide, which can react with alumina to form cobalt aluminate, which is very difficult to reduce to metallic cobalt and alumina. Another example is silica-supported iron oxide. Usually the reduction of iron(III) to iron(II) proceeds readily, because the reduction to iron(II) is hardly thermodynamically limited by the presence of water vapor. Iron(ll), however, reacts rapidly with silica to iron(II) silicate, which is almost impossible to reduce. 

To further test this hypothesis freshly-reduced catalysts were reacted with high-pressure steam (5 atm). A significant loss of BET surface area (from 215 to 188 mVg) is observed after Co/Davisil was reduced at 1 atm and reacted with 5 atm steam for 24 h (see Table 3). Increasing the space velocity by a factor of four also increases the rate of BET surface area loss (from 12.5 % / 24 h to 39.0 % / 24 h). Extents of reduction of cobalt oxide to cobalt metal before and after steam treatment are shown in Table 3. After steam treatment the cobalt oxide-support interaction is apparently substantially increased, i.e., the fraction of cobalt reduced to the metal at 400°C decreases from 89 to 4% moreover, the amount of cobalt-silicates (as inferred from TPR spectra shown elsewhere [22, 23]) also increases after steam treatment. This latter observation is consistent with the substantially higher extent of reduction of these catalysts (71-72%) at 750 C, a temperature at which a significant fraction of cobalt silicate can be reduced to the metal. 

The present research showed a dependence of various ratios of rutile anatase in titania as a catalyst support for Co/Ti02 on characteristics, especially the reduction behaviors of this catalyst. The study revealed that the presence of 19% rutile phase in titania for CoATi02 (C0/RI9) exhibited the highest number of reduced Co metal surface atoms which is related the number of active sites present. It appeared that the increase in the number of active sites was due to two reasons i) the presence of ratile phase in titania can fadlitrate the reduction process of cobalt oxide species into reduced cobalt metal, and ii) the presence of rutile phase resulted in a larger number of reduced cobalt metal surface atoms. No phase transformation of the supports further occurred during calcination of catalyst samples. However, if the ratios of rutile anatase were over 19%, the number of active sites dramatically decreased. 

TEM-EDS and XPS analyses were conducted on Co/MgO catalysts. The results of surface analyses showed that Co metal is not supported on the MgO as particles, but covers MgO surface in the case of 12 wt.% Co/MgO calcined at 873 K followed by reduction. After the reduction of catalyst at 1173 K, both cobalt oxide and CoO-MgO solid solution are observed on the surface of catalyst. In the steam reforming of naphthalene, two types of coke deposited on the surface of catalyst are observed. These are assigned to film-like and graphite type carbon by TPO analysis. 

Fig. 1 compares the activities of vanadium-, cobalt- and nickel- based catalysts in ODH of ethane. Representative catalysts contained between 2.9 and 3.9 wt.% of metal. It is to be pointed out that metal oxide-like species was not present at any of the catalysts, as its presentation is generally the reason in the activity-selectivity decrease. The absence of metal oxide-like species was evidenced by the absence of its characteristic bands in the UV-Vis spectra of hydrated and dehydrated catalysts (not shown in the Figure). The activity of catalysts was compared (i) at 600 °C, (ii) using reaction mixture of 9.0 vol. % ethane and 2.5 vol. % oxygen in helium, and (iii) contact time W/F 0.12 g. i.s.ml 1. These reaction conditions represent the most effective reaction conditions for V-HMS catalysts [4] The ethane conversions, the ethene yields and the selectivity to ethene varied between 13-30 %, 5-16 %, and 37-78 %, respectively, depending on the type of metal species (Co, Ni, V) and support material (A1203, HMS, MFI). 

The oxidation of cobalt metal to inactive cobalt oxide by product water has long been postulated to be a major cause of deactivation of supported cobalt FTS catalysts.6 10 Recent work has shown that the oxidation of cobalt metal to the inactive cobalt oxide phase can be prevented by the correct tailoring of the ratio Ph2cJPh2 and the cobalt crystallite size.11 Using a combination of model systems, industrial catalyst, and thermodynamic calculations, it was concluded that Co crystallites > 6 nm will not undergo any oxidation during realistic FTS, i.e., Pi[,()/I)i,2 = 1-1.5.11-14 Deactivation may also result from the formation of inactive cobalt support compounds (e.g., aluminate). Cobalt aluminate formation, which likely proceeds via the reaction of CoO with the support, is thermodynamically favorable but kinetically restricted under typical FTS conditions.6... 

Supported Rhodium Catalysts Alkali Promoters on Metal Surfaces Cobalt-Molybdenum Sulfide Hydrodesulfurization Catalysts Chromium Oxide Polymerization Catalysts... 

We begin with the structure of a noble metal catalyst. The emphasis is on the preparation of rhodium on aluminum oxide and the nature of the metal-support interaction. Next we focus on a promoted surface in a review of potassium on noble metals. This section illustrates how single crystal techniques have been applied to investigate to what extent promoters perturb the surface of a catalyst. The third study deals with the sulfidic cobalt-molybdenum catalysts used in hydrotreating reactions. Here we are concerned with the composition and structure of the catalytically active... 

Common catalyst compositions include oxides of chromium or molybdenum, or cobalt and nickel metals, supported on silica, alumina, titania, zirconia, or activated carbon. 

Numerous studies have been published on catalyst material directly related to rich catalytic combustion for GTapplications [73]. However, most data are available on the catalytic partial oxidation of methane and light paraffins, which has been widely investigated as a novel route to H2 production for chemical and, mainly, energy-related applications (e.g. fuel cells). Two main types of catalysts have been studied and are reviewed below supported nickel, cobalt and iron catalysts and supported noble metal catalysts. 

While there have been much activity in the literature addressing Fe, Ru and Ni F-T catalysts, the largest body of papers and patents in the last three decades have dealt with Co-based F-T catalysts in attempts to make more active catalysts with high wax selectivities. It is, however, remarkable to notice that modern Co F-T catalysts are still very similar to the ones prepared by Fischer and co-workers i.e., they consist of promoted cobalt particles supported on a metal oxide and most of, if not all, Co-based F-T catalyst compositions contain the following components ... 

Molybdena catalysts have been with us for quite a long time. The term molybdena is used here to denote a composite catalyst consisting of molybdenum oxide supported on an activated support, commonly alumina. Early it was found that certain transition metals, notably cobalt and nickel, promote the molybdena catalyst for hydrodesulfurization (HDS) reactions. 

Catalysts help customers comply cost-effectively with clean-air regulations. Hydrocarbons, carbon monoxide, and nitrogen oxides can be removed using supported precious metal catalysts. Organic sulfur compounds are converted to H2S using nickel/molybdenum or cobalt/molyb-denum on alumina catalysts. Sulfur can be recovered in a Claus process unit. The Claus catalytic converter is the heart of a sulfur recovery plant. 

Dynamic reactor studies are not new, but they have not been widely used in spite of the fact that they can provide a wealth of information regarding reaction mechanisms. In this research, oxidation of carbon monoxide over supported cobalt oxide (C03O4) was studied by both dynamic and conventional steady state methods. Among metal oxides, cobalt oxide is known to be one of the most active catalysts for CO and hydrocarbon oxidation, its activity being comparable to that of noble metals such as palladium or platinum. 

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