This study is about reduction reaction making 2, 4-dinitrotoluene (2, 4-DNT) to 2, 4-toluene diisocyanate (2,4-TDI) with Pd/SiO2. Catalytic systems based on Pd/SiO2 at about 200 ℃ and under 100 bars of carbon monoxide. We studied the effect of pyridine on the yield of the TDI. TDI was not created without pyridine, but created with pyridine, at the reaction result. According to research, homogeneous synthesis of TDI with direct carbonylation, palladium and pyridine complexion is known to catalyze. When adding pyridine the reason of TDI synthesis is palladium leaching, ICP-AES was performed to confirm it. As a result, the proportion of Pd loaded in SiO2 was decreased 52% than before, after the reaction by adding 20 vol% pyridine. Generating TDI by adding pyridine might be the effect of the complex ion, which is composed of leached palladium and pyridine.