The synthesis system of uniform and well-crystallized alloy nanoparticulate catalysts has been studied based on the calculation of pH dependent metal complex concentrations in an aqueous solution. Results of both the prediction based on calculation and EXAFS analysis clearly demonstrated that [Pd2+(EDTA)] and Te-citric acid complex species were generated independently in the solution. Since the formations of metal complexes are restricted to [Pd2+(EDTA)] and Te-citric acid complexes in the pH range between 5 and 10, only Pd20Te7 was successfully synthesized when the reducing agent was introduced into the [Pd2+(EDTA)] complex/Te-citric acid complex system at room temperature. Moreover. PdTe nanoparticles can be synthesized predominantly in pores of silica-gel by controlling the temperature of the Pd-EDTA/Te-citric acid/hydrazine mixed solution with a metal loading of 0.5 wt% Pd. The main phase of the well-crystallized alloy nanoparticles formed in the pores was Pd20Te7, leading to remarkable stability in catalytic activity, compared with those of the conventional catalysts. (C) 2010 Elsevier B.V. All rights reserved.