We report a theoretical model to describe the spatiotemporal dynamics of a new system consisting of sul de ions di¤using into an organic gel containing mercaptoethanol-capped cadmium ions. The product, cadmium sul de, exhibits a faint yellow transparent propagating front starting at the gel-outer electrolyte interface. When subjected to UV light, this system reveals uorescing CdS nuclei localized spatially in a narrow region (constant width), called pulse, that leads the front and propagates down the tube. The reported model is based on reaction-di¤usion equations coupled to dynamical competitive particle growth. The resulting evolution equations were solved numerically and the results are shown.