NOVELTY - A semi-permeable particle comprises water-insoluble semi-permeable polymer providing continuous polymeric phase including an external particle surface, where semi-permeable particle further comprising multiple discrete cavities within continuous polymeric phase, and a cavity stabilizing hydrocolloid disposed within multiple discrete cavities, where semi-permeable particle being permeable to molecules having molar mass of less than or equal to 1000 Daltons, where semi-permeable particle has a mode particle size of 1 mu m and comprises nanoparticles of catalytically active metallic materials.    USE - As semi-permeable particle (claimed), used in drug delivery devices, cosmetic formulations, pharmaceuticals and diagnostic and analytical devices, and chemical reactors used for organic syntheses or other chemical processes, food processing, laundering, waste water treatment, air pollution abatement, bio fuels refining, fuel cells, convertors, or any applications where catalytically active metallic material is needed for a chemical reaction.    ADVANTAGE - The semi-permeable particles have multiple discreet cavities allow diffusion of the intended small molecule reactive chemicals so that they interact with the catalytically active metallic materials present in the multiple discrete cavities. This provides desired rapid reaction rates while allowing convenient isolation of those catalytically active metallic materials after use. Similarly, isolation of a reaction product obtained using the catalytically active metallic materials contained in the semi-permeable polymer particles, is facilitated so that contamination is minimized. The uniform size of the semi-permeable particles leads to consistent reaction rates and recovery processes. In addition, the semi-permeable particles need not be isolated or dried before they are used. The semi-permeable particle allow for their recovery by simple filtration or centrifugation. Little or no nanoparticles are lost from the semi-permeable particles when they are recovered.    DETAILED DESCRIPTION - A semi-permeable particle comprises a water-insoluble semi-permeable polymer providing continuous polymeric phase including an external particle surface, where the semi-permeable particle further comprising multiple discrete cavities within the continuous polymeric phase, and a cavity stabilizing hydrocolloid disposed within at least some of the multiple discrete cavities, where the semi-permeable particle being permeable to molecules having a molar mass of less than or equal to 1000 Daltons, where the semi-permeable particle has a mode particle size of at least 1 mu m and comprises nanoparticles of catalytically active metallic materials disposed within at least some of the multiple discrete cavities, which nanoparticles of catalytically active metallic materials (a) comprise at least one element selected from Groups 8, 9, 10, and 11 of the periodic table, and (b) have an effective diameter of at least 1 nm and up to and including 200 nm. INDEPENDENT CLAIMS are included for the following:    (1) aqueous slurry of multiple semi-permeable particles;    (2) making an aqueous dispersion of semi-permeable particles, involving providing a first aqueous phase comprising the nanoparticles of catalytically active metallic materials and the cavity stabilizing hydrocolloid, both dispersed within the first aqueous phase, dispersing the first aqueous phase in an organic solvent comprising a water-insoluble polymer to form a first emulsion, dispersing the first aqueous phase in an organic solvent comprising the water-insoluble semi-permeable polymer to form first water-in-oil emulsion, dispersing the first water-in-oil emulsion in a second aqueous phase containing a surface stabilizing material to form a water-in-oil-in-water emulsion containing droplets of the water-in-oil emulsion, and removing the organic solvent from the droplets to form the aqueous dispersion of semi-permeable particles; and    (3) causing a chemical reaction involving contacting reactive chemicals having a molar mass of less than or equal to 1000 Daltons with a slurry of semi-permeable particles, each of the semi-permeable particles comprising a water-insoluble semi-permeable polymer providing a continuous polymeric phase including an external particle surface, where the semi-permeable particle further comprises multiple discrete cavities within the continuous polymeric phase, and cavity stabilizing hydrocolloid disposed within at least some of the multiple discrete cavities.