NOVELTY - An aqueous slurry of semi-permeable particles (A1) comprises a water-insoluble, semi-permeable polymer providing a continuous polymeric phase including an external particle surface; and multiple discrete cavities within the continuous polymeric phase, and having disposed within at least some of the multiple discrete cavities: (a) a cavity stabilizing hydrocolloid, and (b) an aqueous solution or suspension of an organic catalytic material.    USE - As aqueous slurry of semi-permeable particles useful for making material for catalyzing chemical reactions in substantially aqueous media (claimed); in drug delivery devices, cosmetic formulations, fuel cells, 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, bio fuels refining, or in applications where an organic catalytic material is needed for a chemical reaction.    ADVANTAGE - The semi-permeable particles are impermeable to the organic catalytic materials so they are retained within the multiple discrete cavities, and the semi-permeable particles can be reused multiple times for the same or different chemical reaction. The organic catalytic materials used can be very expensive and difficult to isolate for recovery and reuse. The relatively large semi-permeable particles in which they are incorporated allow for their recovery by simple filtration or centrifugation. Little or no organic catalyst material is lost from the semi-permeable particles when the particles are recovered and this provides considerable economic advantages. At least 80% of the organic catalytic material is retained in the semi-permeable particles during storage and on repeated reuse as a catalyst in chemical reactions. At least 80% of the organic catalytic material is retained in the semi-permeable particles after storage for more than 30 days at room temperature as aqueous slurry. The semi-permeable particles have multiple discreet cavities that allow diffusion of the intended small molecule reactants so that they interact with the organic catalytic material present in at least some of the multiple discrete cavities. This provides desired rapid reaction rates while allowing convenient isolation of the organic catalytic material after use. Similarly, isolation of the reaction product from the organic catalytic materials 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. Rather, they are advantageously used in aqueous slurry.    DETAILED DESCRIPTION - An aqueous slurry of semi-permeable particles (A1), each semi-permeable particle comprises a water-insoluble, semi-permeable polymer providing a continuous polymeric phase including an external particle surface, each semi-permeable particle further comprises multiple discrete cavities within the continuous polymeric phase, and having disposed within at least some of the multiple discrete cavities: (a) a cavity stabilizing hydrocolloid, and (b) an aqueous solution or suspension of an organic catalytic material, and each semi-permeable particle has a mode particle size of at least 1 mu m, where each semi-permeable particle is impermeable to the organic catalytic material, and the semi-permeable particle is permeable to molecules having a molar mass that is less than or equal to 1000 Daltons. INDEPENDENT CLAIMS are included for the following:    (1) a material useful for catalyzing chemical reactions in substantially aqueous media comprising the aqueous slurry of semi-permeable particles (A1);    (2) making an aqueous slurry of several semi-permeable particles involving providing a first aqueous phase comprising the organic catalytic material and the cavity stabilizing hydrocolloid, both dispersed within the first aqueous phase, dispersing the first aqueous phase in an organic solvent comprising the water-insoluble semi-permeable polymer to form a 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 several semi-permeable particles; and    (3) causing (M1) 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 (A1).