Micro-heterogeneous catalysis at the surface of electrodynamically levitated particles

The results of a base promoted ester hydrolysis reaction on laboratory generated particles with net charge that were stored in an electrodynamic balance are presented. In particles with net positive charge the hydrolysis did not occur to a measurable extent in a 2 h period. Conversely, in particles with net negative charge, the rate of the hydrolysis reaction was promoted to a high level. These data suggest that the ester solute partitioned onto the surface of the particle, on top of a diffusion layer. This diffusion layer is analogous to one-half of an electric double layer, and it contained the net charge carried by the particle. Depending on the polarity of the ions in the diffusion layer, the ester hydrolysis was prevented (cations) or promoted (anions) by acting, respectively, as a barrier or a conduit for hydroxide ions from the core of the particle to the laver of ester. These data have provided much information concerning solute dynamics within particles with net charge, and they imply that surface structure, defined by net charge and partitioning of solute and solvent, are important factors that determine the heterogeneous and multiphase chemistry of a particle. (C) 2001 Elsevier Science Ltd. All rights reserved.