Particle size reduction precipitation method

Physico-chemical methods for particle size reduction comprise methods wherein the substance is first dissolved and then precipitated in a finer form during further processing. This has the advantage that it is independent of the fineness of the starting material and that the formation of small agglomerating particles is largely prevented. Two methods are distinguished the solution method and the precipitation method. 

Supported Pd nanoparticles were obtained using simplified microemulsion method. The resitits suggest that one step reduction-precipitation method allows obtaining supported Pd nanoparticles with small average size. The average palladium nanoparticle size can be controlled by changing the chemical composition of the microemulsion. The smaller nanoparticles were obtained with AOT surfactant. The differences in the particles size were ascribed to the different ionicities of the surfactants or solvent polarities. 

The magnetic method has been applied in studying the growth of the nickel particles due to the reduction process for the co-precipitated sample 5421. Reduction treatments have been performed at various temperatures in the range 400-600° C. (for which the reduction is assumed to be complete) and during various periods of time (% to 16 hrs.). Particle sizes of the products were characterized by the magnetic parameter a. 

Nanostructured LaNiOs was prepared by co-precipitation under ultrasonic radiation [120], Using various characterization methods and evaluation of catalytic activity, the effects of ultrasound on the structural properties and catalytic activity of LaNiOs were studied. The TEM showed that the ultrasound could cause a decrease in the particle size. The average particle size of LaNiOs prepared by sonochemistry is 20 nm. The specific surface area of LaNiOs is 11.27 m g h Ultrasound could lead to increased surface oxide content and surface crystal oxygen vacancies. The TPR result showed that the LaNi03 prepared by sonochemistry has a lower reduction temperature and a higher ratio of surface oxygen to crystal oxygen. The evaluation of catalytic activity showed that ultrasound could increase the catalytic activity of LaNiOs for NO decomposition. 

A supercritical anti-solvent precipitation technique has been used to prepare a novel Titania catalyst support. The Titania precursor was prepared by precipitating TiO (acac)2 from a solution of methanol using supercritical carbon dioxide at 110 bar and 40°C. The surface area of the supercritical precursor was 160 m g and this decreased to 35 mV after calcination, although there was no significant reduction of particle size. The new titania support was used to prepare a supported gold catalyst and this was tested for ambient temperature carbon monoxide oxidation. The supercritical catalyst demonstrated notably high activity when compared with catalysts prepared by other nonsupercriticd methods. 

For the preparation of gold nanopartides supported on insoluble solids, the most widely used procedure is the precipitation-deposition method [32-36]. Starting from an aqueous solution of HAuCh, addition of a base leads to precipitation of a mixture of Au(OH)3 and related oxy/hydroxides that adsorbs into the solid and is then reduced to metallic gold by boiling the adsorbed species in methanol or any other alcohol. In this procedure, it has been established that the pH of the precipitation and the other experimental conditions (nature of the alcohol, temperature and time of the reduction, calcination procedure, etc.) can provide a certain control of the particle size of the resulting nanoparticles [3j. Figure 12.2 illustrates the steps required in the formation of supported gold nanoparticles. 

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