Aluminates formation

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... 

Bolt, H. 1994. Transition metal-aluminate formation in alumina-supported model catalysts. PhD thesis, University of Utrecht. 

Goodwin and coworkers have studied the formation of cobalt aluminates.25,26 Jongsomjit et al. studied cobalt aluminate formation by TPR and RAMAN spectroscopy.26 The catalysts investigated were 25% Co/y-Al203 and Ru-promoted (0.5%)-25% Co/y-Al203. The Raman spectra of the samples after various pretreatments are shown in Fig. 3. 

A. Sirijaruphan, A. Horvath, J. G. Goodwin, Jr and R. Oukaci, Cobalt aluminate formation in alumina-supported cobalt catalysts effects of cobalt reduction state and water vapor, Catal. Lett., 2003, 91, 89-94. 

The aluminate formation with some minor variations was also proposed by Sabatier and Reid (4). This theory was recently revived by Topchieva et al. (5). 

Some bulk cobalt aluminate formation is expected to take place for the boehmite based catalyst, owing to a Hedvall effect (24).The spectrum of adsorbed pyridine on CoMo-124 B shows indeed a weaker 1612 cm l band, comparable with the intensity of this band for the MoCo-123 catalyst. This indicates that about 25 % of the cobalt ions has disappeared in the bulk of the alumina. (Figure lid). 

Similar interactions have been observed for the nickel promoted catalyst. However, the degree of interaction depends on the calcination temperature. This interaction disappears for a great part at increasing temperatures. This is ascribed to bulk nickel aluminate formation. 

Numerous characterizations of catalysts after real driving conditions and various mileages on different vehicles, show, among other features, Pt/Rli alloying and cerium aluminate formation [12]. Tlie similarity of these results with oin own observations on commercial samples suggest that the laboratory procedures described herein allow to reproduce significant behaviom of catalysts under real driving conditions. 

Kinetic measurements on reactions of Li, Na, and K carbonates and hydroxides with AI2O3 show that the rates of aluminate formation are in the order Li+ > Na+ > K+for carbonates, and Na+ > K+ > Li+for hydroxides. 

Unlike the supported noble metals discussed so far, where it is customary, although not always justifiably so, to assume that all of the metal is present in its reduced state following pre-treatment in hydrogen, for base metal catalysts such as supported Ni, it is quite common to find a fraction present in an unreduced state. This is not confined to alumina and the consequence of Ni aluminate formation," but is also common for silica" and silicate supported... 

Sodium dihydridobis-(2-methoxyethoxo)aluminate Formation of phosphorus-carbon bonds Phosphine oxides from phosphinic acid esters... 

A comparative analysis of the kinetics of La2SrFe207 and La2SrAl207 formation shows that the degree of the aluminate conversion in 24 h at 1300°C does not exceed 0.2, and for the ferrite it is 0.8. This fact indicates that the rate of the ferrite formation considerably exceeds the rate of the aluminate formation and requires lower temperatures. This does not hold for Gd-containing compounds Gd2SrAl207 is formed mueh faster than Gd2SrFc207. 

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