Other Systems Involving Size Reduction

Other Systems Involving Size Reduction Industrial applications usually involve a number of processing steps combined with size reduction [Hixon, Chem. Eng. Progress, 87, 36-44 (May 1991)]. 

Most methods deal with the formation of metal particles on a support that is preformed since this leads to simpler preparation processes. There is an important route, however, typically used for metal-SiCh and metal-AI2O3 catalysts, which involves (Table I) the coprecipitation in a precursor form (hydroxides, nitrates, carbonates, silicates, etc.) of both the support and the active phase from a solution 37a,b, 38, 41). The advantage is to produce an intimate mixing of metal precursor and support. The precipitate leads on calcination to a support with the active component dispersed throughout the bulk as well as at the surface. After reduction to the final catalyst, it is difficult to obtain metal crystallites of uniform size 42, 43) because of the presence of both the oxides (of the support and of the active metal) and other intermediate compounds [e.g., nickel alumi-nate or silicate for the Ni/Al203 42) and Ni/SiCh 43) systems, respectively] that have different reducibilities. 

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