Cobalt oxide sintered

Deactivation is a common and important phenomenon in FTS. Deactivation effects of water are recorded on all commonly used supports. The suggested mechanisms include oxidation, sintering and solid state reactions rendering cobalt inactive. 

There seems to be several mechanisms leading to the activity loss oxidation of cobalt metal, sintering of cobalt metal particles as well as sintering of the support and formation of stable cobalt-support metal oxides (silicates or aluminates). Oxidation by water is a key issue, possibly occurring on all supports and on unsupported cobalt. A thermodynamic analysis of this effect was reported by van Steen et al.,40 and they describe the FTS reaction system in terms of reactions (1) and (2) below ... 

One example is a catalyst consisting of gold on cobalt oxide particles supported on a mechanical mixture of zirconia-stabilised ceria, zirconia and titania, that survived 773 K for 157 h, with some deactivation [145]. Grisel and Nieuwenhuys [38,127] have shown that the addition of transition metal oxides to form Au/MO j/ADOs catalysts, massively suppresses Au particle sintering in methane oxidation tests up to 973 K. Also, Seker and Gulari [30] found that Au/ADOs catalysts survive rigorous pre-treatments of 873 K in air for 24 h, followed by several cycles of 423-773 K and they were then kept... 

TPO experiments were performed for the reduced catalysts in order to investigate the stability of these systems towards gas phase oxygen (Fig. 3). The perovskites were completely reduced in a TPR experiment with a stream of 10% H, in Ar heating from room temperature to 923 K at a rate of 10 K/min. The temperature was then rapidly decreased to avoid sintering of the cobalt metal and TPO analysis performed. TPO profiles showed that the oxidation takes place in two steps. The first one at near 473 K (peak I) has an oxygen consumption which suggests that the cobalt is oxidised to two Co and one Co 7 rherefore, this oxidation probably corresponds to the formation of the cobalt oxide spinel according to the reaction ... 

The active material in the positive electrode is nickel hydroxide. Usually, the nickel hydroxide has a conductive network composed of cobalt oxides and a current collector which commonly is a nickel foam skeleton, but may alternately be a nickel fiber matrix or may be produced by sintering filamentary nickel fibers. ... 

Semiconductor thermometers can be built in many shapes. Frequently they are very small beads, so that their heat capacity and thermal lag are small. They may also be made in form of large disks, so that they can average the temperature over a larger object. Typical materials which are used in thermistor thermometers are iron oxide, magnesium chromate, magnesium aluminate or sintered mixtures of nickel oxide, manganese oxide and cobalt oxide. 

Bartholomew and coworkers32 described deactivation of cobalt catalysts supported on fumed silica and on silica gel. Rapid deactivation was linked with high conversions, and the activity was not recovered by oxidation and re-reduction of the catalysts, indicating that carbon deposition was not responsible for the loss of activity. Based on characterization of catalysts used in the FTS and steam-treated catalysts and supports the authors propose that the deactivation is due to support sintering in steam (loss of surface area and increased pore diameter) as well as loss of cobalt metal surface area. The mechanism of the latter is suggested to be due to the formation of cobalt silicates or encapsulation of the cobalt metal by the collapsing support. 

Thermistor basedflow-through calorimetric sensors. Enzyme thermistors make the most widely developed type of heat measurement-based sensors. The thermistors are normally used as temperature transducers in these devices. Thermistors are resistors with a very high negative temperature coefficient of resistance. They are ceramic semiconductors made by sintering mixtures of metal (manganese, nickel, cobalt, copper, iron) oxides. Like the two previous groups, thermistor sensors do not comply strictly with the definition of "sensor" as they do not consist of transducers surrounded by an immobilized enzyme rather, they use a thermistor at the end of a small... 

---