Palladium (Pd), silver (Ag), and Pd₅₀/Ag₅₀ alloy colloids were prepared as hydrogenation catalysts by γ-irradiation in aqueous and organic solvents. The MCM-41 embedded with Pd, Ag, and Pd₅₀/Ag₅₀ alloy nanoparticles (PdMCM-41, AgMCM-41, and Pd/AgMCM-41, respectively) were also prepared as hydrogenation catalysts by hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of Pd, Ag, and Pd₅₀/Ag₅₀ alloy colloids prepared by γ-irradiation. The MCM-41, PdMCM-41, AgMCM-41, and Pd/AgMCM-41 samples were characterized by both transmission electron microscopy (TEM) and X-ray diffraction (XRD). The precious metallic and alloy nanoparticles were partially embedded in the surface of MCM-41. The hydrogenation of cis, cis-1,3-cyclooctadiene (COD) was performed using the Pd, Ag, and Pd₅₀/Ag₅₀ colloids as homogenous catalysts and PdMCM-41, AgMCM-41, and Pd/AgMCM-41 as heterogeneous catalysts. Cyclooctene was obtained selectively by hydrogenation of cis,cis-1,3-COD using Pd₅₀/Ag₅₀ colloids as a homogenous catalyst for 20 min, and using PdMCM-41 as heterogeneous catalyst for 60 min.