Features during calcination

One of the first cells that allowed exposure of the catalyst sample to reaction conditions was developed by Schrader and coworkers (Cheng et al., 1980) key feature of the design is the placement of the catalyst, which is pressed into a wafer, on a rotor. The authors investigated the structural evolution of alumina-supported molybdenum oxide catalysts during calcination. Chan and Bell (1984) reported on the formation of... 

Figure 9.28 RBS proves that chromate can indeed desorb from the model catalyst during thermal activation. A wafer with 10 Cr/nm2 loading features 7.0 Cr/nm2 after calcination at 550 °C. The desorbing chromate readily readsorbs on an empty silica surface placed opposite to the loaded wafer (courtesy of...

Another method of analysis makes use of a subtraction procedure and has been applied to investigate the oxidation state of a series of Ce-Zr mixed oxides during a temperature programmed process [195]. A difference spectrum between the sample at a defined state and the calcined, fully oxidized material displays a positive peak at the position of feature Bo, characteristic of Ce, and a negative peak at the position of feature C, characteristic of Ce. The overall peak-to-peak amplitude is then proportional to the average reduction degree of Ce in the sample. 

The results that have been obtained with the catalysts after reduction and passivation are the same as those after calcination, i.e. the textural and structural properties of the support material have completely been retained after the treatments (as determined with nitrogen physisorption. X-ray diflfiaction and transmission electron microscopy). Information concerning the metallic nickel particles has been obtained with X-ray diffraction and transmission electron microscopy. Diflractograms of the catalysts after passivation are shown in Fig. 8. The observed features are exactly the same as for the oxidic systems (Fig. 4) only very broad and low diffractions are visible for the catalyst ex citrate, whereas sharp, intense peaks with a broad onset are observed for the catalyst ex nitrate. Consequently the nickel particles of the catalyst ex citrate have resisted sintering during the reduction treatment, thereby conserving the high dispersion of the catalyst. These results were confirmed by transmission electron microscopy measurements (not shown) only very small nickel nanoparticles situated inside the mesopores were found for the catalyst ex citrate. 

The combination of spectral techniques and reaction results revealed contrasting features for the Ni-Al and Mg-Al hydroxide systems as they undergo calcination. The Ni-Al hydroxide after calcination showed the distinct presence of NiO and tetrahedrally coordinated Al, and a lack of octahedrally coordinated Al. 2-Propanol decomposition studies showed that Ni-Al and NI systems display similar selectivity. This suggests that during... 

Fig. 44. Different from other ID feature, few researches have reported the ID Bi2MOg with microtube structure. Similar with the preparation method adopted by Sun et al, Zhang et used electrospun polyacrylonitrile microfibers as template to develop tube-like structure of Bi2MOs. During this preparation process, the diameter of template is related with the in-diameter of obtained ID Bi2MOe microtube. Besides, the calcinations temperature must be strictly controlled to avoid the structural collapse.

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