Spherical catalysts, preparation

Table 4.10 Mechanical strength and spherical coefficient of the spherical catalyst prepared by spraying method...

Figure 3.12 Schematic representation of the dispersion of Zr02 particles and the extent to which the silica support is covered in three Zr02/Si02 catalysts prepared by impregnation with an aqueous zirconium nitrate solution, and one prepared via an exchange reaction of the support with zirconium ethoxide. The rectangles represent 100 nm2 of silica support area, and the circles represent a half-spherical particle of Zr02 seen from above. See Table 3.3 for corresponding numbers (adapted from Meijers et al. [33]).

Figure 1.6 Representative TEM image (a) and particle size distribution (b) obtained for a Au/Ti02 catalyst prepared by grafting of a [Au6(PPh3)6](BF4)2 complex onto Ti02 particles followed by appropriate reduction and oxidation treatments [42], The gold particles exhibit approximately spherical shapes and an average particle size of 4.7 nm.The measured Au particle sizes could be well correlated with the activity of the catalyst for carbon monoxide oxidation and acetylene hydrogenation. (Reproduced with permission from Springer.)...

The ultimate goal of catalyst preparation is to obtain very small platinum particles to increase the surface to volume ratio (S/V = 3/r for a spherical particle). Platinization by ion exchange and impregnation with colloidal platinum yield the best results in this respect (135). 

By use of this technique, it is possible to prepare fine spherical catalyst particles in the 10-100/rm diameter range, as arc required for typical fluidized-bed catalytic processes. In this technique used for large-scale catalyst manufacture, the feed is generally dilute hydrogel or sol that is sprayed from the top of a tower while hot air is blown in a cocurrcnt or countercurrent direction to dry the droplets before they reach the bottom of the tower. The fine droplets arc produced or atomized by pumping the hydrogel or sol under pressure cither... 

Laboratory tests were made of catalysts prepared on spherical alumina supports and on monolithic catalysts. The spherical catalysts were prepared by a proprietary technique, and were protected against shrinkage by use of a chemical stabilizer. The monoliths were wash-coated with alumina prior to impregnation with the metals. The catalysts were tested fresh and also after thermal treatment (10 hrs at 1094°C in a perfluent atmosphere consisting of 10% H20 in air). 

The preparation of sulphated zirconia designed for catalyst supports was studied by Boutonnet et al. . Zirconia prepared in microemulsion showed a pure tetragonal structure compared with zirconia prepared by an impregnation -precipitation procedure which also contained monoclinic phase. Platinum-promoted sulphated zirconia catalysts were prepared both in anionic and non-ionic microemulsions. Furthermore, the catalytic activity and selectivity for the isomerization of hexanes were tested. The catalysts produced by the microemulsion method showed a higher selectivity towards isomers but a lower activity when compared to catalysts prepared by impregnation technique. More recently, a study of zirconia synthesis from micro and macroemulsion systems has been conducted . Spherical ZrOa particles ranging from tens of nanometers to a few micrometers were produced. 

With this structure, PO is selectively produced, implying that the simultaneous reaction of 311,5 with O2 and H2 is the predominant reaction path. This reaction is always accompanied by H2 combustion to form H2O, and this results in higher yields of H2O than of PO. On the other hand, use of the impregnation method for catalyst preparation gives spherical Au NPs, which are larger than 30 nm in diameter and only interact weakly with the Ti02 support. With this structure PO is not... 

In addition, Xin et al. [115] prepared multiwalled carbon nanotube-supported Pt (Pt/MWCNT) nanocomposites by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution (EG). For comparison, a Pt/XC72 nanocomposite was also prepared by the EG method. The Pt/MWCNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal particles with a narrow particle-size distribution. 

UCI in USA introduced 73-03-2 spherical catalyst containing cobalt. The catalyst is prepared via powder sintering method. The process technology and devices was complex, and it was hard to produce catalysts with small particles. The particles of the catalysts are so large that the advantages of small particles which have high activities are completely lost. 

Preparation Technique of Spherical Catalysts 4.6.1 Shaping technique of catalysts... 

Preparation technique of spherical catalysts for ammonia synthesis... 

As the spherical catalyst is prepared by quencher in water or aqueous solution, there are some differences between the spherical catalyst and the irregular catalyst cooled indirectly (such as air-cooled or water jacket cooled catalyst) as follows ... 

Catalysts may be porous pellets, usually cylindrical or spherical in shape, ranging from 1/16 to 1/2 inch in diameter. Small sizes are recommended, but the pressure drop through the reactor increases. Other shapes include honeycombs, ribbons, wire mesh, etc. Since catalysis is a surface phenomena, an important physical property of these particles is that the internal pore surface may be many magnitudes greater than the outside surface. The reader is referred to the remainder of this chapter for more information on catalyst preparation, properties, comparisons, costs, and impurities. 

A wide variety of different magnesium compounds have been investigated to produce highly-active ethylene polymerization catalysts. The characteristics of the polymers produced with highly-active Mg/Ti-based catalysts are determined by the type of magnesium-containing compound used in the catalyst preparation. But the important characteristics of the finished solid catalyst material include polymerization kinetic profile, particle size, particle size distribution, and particle shape (spherical or irregular). 

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