Particle splitting, catalysts

Particle splitting is not merely of academic interest. Recently, it has been demonstrated that three-way automotive exhaust catalysts can be made from supported palladium alone, rather than from rhodium and platinum. The opportunity results in part from improvements in technology that permit palladium to be redispersed by a particle-splitting process during lean-bum periods. Possibly this redispersion results from palladium particle splitting. 

However, when using supports with weak linkage between the primary particles of the catalyst, its splitting occurs quickly and it is unlikely to influence the shape of the kinetic curve. For example, in the case of chromium oxide catalyst reduced by CO supported on aerosil-type silica, steady-state polymerization with a very short period of increasing rate is possible (see curve 1, Fig. 1). 

The calculation of C according to (6) shows (95) that if the catalyst splitting results in the formation of catalyst pellets about 1000 A in size, then even under the most unfavorable conditions (the concentration of the active centers is equal to the total chromium content in the catalyst, 2r2 = ) the diffusional restriction on the primary particle level is negligible. 

Thus, two factors may be pointed out that determine the possibility of obtaining high yields of crystalline polyethylene on a solid catalyst with no diffusional restriction (1) the splitting up of the catalyst into small particles (< 1000 A), possible when using supports with low resistance to breaking (2) the formation of polymer grains with polydispersed porosity. 

Cadmium sulfide has been proposed as a catalyst for the splitting of water by sunlight In these studies, the CdS particles were loaded with colloidal RuO in... 

Zheng et al. investigated the NH3 splitting over Ru catalysts supported on differently treated CNTs. They observed a negative particle size effect, i.e., the H2 formation rate decreases at higher dispersion of the active component [37]. ft was also shown that... 

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