Magnetite alumina

The reduced magnetite with alumina was found to have a N2 BET surface area of 29 m per gram of catalyst. When adsorbing N2 dissociatively it was found that 2.2 mL [standard conditions, i.e. 273 K and 1 bar (= 100000 Pa)] of N2 could be adsorbed per gram of catalyst. Assuming that the atomic nitrogen forms a c(2x2) overlayer on the Fe(lOO) surface determine the iron area per gram of catalyst. The lattice distance of iron is 0.286 nm. 

Gold, chloride, adsorption, magnetite, goethite, alumina, titanium dioxide, hydrometallurgy... 

Figure 6.6 In situ XRD of an alumina-supported iron catalyst during reduction in H2 at 675 K reveals the transition of a-Fe202 (hematite) via Fe(04 (magnetite) to metallic iron as a function of time. The graph shows the degree of reduction of supported and unsupported oc-Fe203 as determined from the XRD measurements (from Jung and Thomson f 14]).

Tewari, P.H. McClean, A.W. (1972) Temperature dependence of point of zero charge of alumina and magnetite. J. Colloid Interface Sci. 40 267-272... 

This microwave-assisted reaction was carried out on a 3-g scale in a glass vessel placed in a bath of alumina/magnetite. The anthraquinone (m.p. 284°C) produced was collected as it sublimed from the reactor. Further, o-benzoylbenzoic acid was added and the reaction repeated. The main advantage of the microwave-assisted reaction lies in the recycling of the catalyst. The yield in the conventional heating process falls to 50% after four uses of catalyst, whereas in the microwave-assisted process the yield is still 84% after fifteen uses. 

Ammonia synthesis catalysts have traditionally been based on iron and have been made by the reduction of magnetite (Fe304). The difference between different commercially available products lies in optimized levels of metal oxide promoters that are included within the magnetite structure. These metal oxides promote activity and improve the thermal stability of the catalyst. Typical promoters are alumina (AI2O3X potassium oxide (K2O), and calcium oxide (CaO). The interactions between the many components in the catalyst can radically affect 1) the initial reducibility, 2) the level of catalyst activity that is achieved, 3) the long-term catalyst performance and 4) the long-term catalyst stability204. 

Diffraction patterns can be used to identify the various phases in a catalyst. An example is given in Fig. 10.3b, where XRD is used to follow the reduction of alumina-supported iron oxide at 675 K as a function of time. The initially present oc-Fe2C>3 (haematite) is partially reduced to metallic iron, with Fe3C>4 (magnetite) as the intermediate. The diffraction lines from platinum are due to the sample holder [10]. 

The raw materials — usually, natural magnetite, lime, potash, and alumina — must, as far as possible, be free of catalyst poisons (see Section 3.6.1.5). Many ores have too high a content of free or bound silica, which can be lowered with magnetic separators [344], Melting is accomplished in electrical resistance or induction furnaces (arc furnaces in the past) operating at 1600-2000 °C. The walls of these furnaces should... 

FIG. 13.6. (a) The relation of the structure of 0-alumina, NaAli 1O17, to that of spinel (after Beevers and Ross). Large circles represent Na, small ones O, and black circles Al. (b) The relation of the structure of magneto-plumbite, PbFei jOij, to that of magnetite Fe304 (after Adelskold). Large circles represent Pb, small ones O, and black circles Fe. 

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