In a combination of generation and storage of hydrogen gas, both formic acid (FA) and acetic acid (AA) have been notified as efficient hydrogen carriers. This study was conducted to synthesize the monometallic catalysts namely palladium (Pd), copper (Cu), and zinc (Zn) on graphitic-carbon nitride (g-C₃N₄) and to study the potential of these catalysts in FA and mixed formic acid (FA)-acetic acid (AA) decomposition reaction. Several parameters have been studied in this work such as the type of active metals, temperature, and metal loadings. The mass percentage of Pd, Cu, and Zn metal used in this experiment are 1, 3, and 5 wt%, respectively. At low temperature of 30 °C, 5 wt% Pd/g-C₃N₄ catalyst yielded higher volume of gas with 3.3 mL, instead of other Pd percentage loadings. However, at higher temperature of 70 °C and 98% FA concentration, Pd with 1 wt%, 3 wt%, and 5 wt% of loading over g-C₃N₄ has successfully produced optimum gas (H₂ and CO₂) of 4.3 mL, 7.4 mL, and 4.5 mL in each reaction, respectively. At higher temperature, Pd metal showed high catalytic performance and the most active element of monometallic system in ambient condition. Meanwhile, at higher percentage of Pd metal, the catalytic decomposition reaction also increased thus producing more gas. However, it can be seen the agglomeration of the particles formed at higher loadings of Pd (5 wt%), and remarkably lowering the catalytic activity at higher temperature, while higher activity at low temperature of 30 °C. The result also showed low catalytic decomposition reaction for Cu and Zn catalyst, due to the small formation of Cu and Zn metal, but presence of high metal oxide (CuO) and (ZnO) promotes the passive layer formation on the catalyst surface.