Studies of the sintering of supported metals over the past decade have emphasized (1) the use of sophisticated spectroscopies and surface-science techniques in combination with industrially-relevant and model catalyst systems to better understand the mechanistic aspects and (2) the analysis of available kinetic data for sintering with more physically-meaingful models. The recent experimental work reveals the complexities of sintering and redispersion processes, which include for example, dissociation/emission of metal atoms from crystallites, diffusion of atoms and crystallites across support surfaces, wetting and spreading of crystallites in oxygen, rupture of films and nucleation of particles in H2, coalescence and/or bridging of two particles, capture of atoms by particles, epitaxy of metal clusters with support surfaces, restructuring and faceting of metal surfaces by different atmospheres and the formation of compounds such as surface aluminates in steam or O2. Sintering rate data obtained over the past four decades have been reanalyzed using the new General Power Law Expression (GPLE), which provides the capability of treating these data in a consistent, unifying fashion such that quantitative comparisons of effects of reaction conditions and catalyst properties are possible for the first time.

Sintering and redispersion of supported metals: Perspectives from the literature of the past decade

High purity nanoporous silica was fabricated using Shirasu volcanic ash as a starting material. The starting materials were placed into a platinum crucible and were melted at 1400°C. A mother glass was formed by quenching the melt in pure water. Leaching was performed by immersing the mother glass into an HCl solution. Nonsilica phases formed by phase separation in the mother glass were leached out with acid solution. The obtained porous silica was more than 99% pure and had pore size smaller than 2 nm. In order to control the pore size, post heat treatment was performed. The pore size could be controlled from 3.1 to 21.7 nm by changing the post treatment temperature.

Issei Fujiyoshi

Papers

Effects of the support and sintering on hydrogen uptake of nickel supported on porous vycor glass