Preparation of calcium oxide catalyst (CaO) from Mangrove clam shells (Geloina expcinsci) by decomposition at various temperatures i.e. 600, 700, 800, 900, 1000 and 1100°C. The XRD result shows peak of 20 : 32,2°, 37,4°, 54,0°, 64,3° and 67,5° for decomposition at 1100°C similar with diffraction of CaO from JCPDS Standard. The FT-IR spectrum shown special characteristics of CaO vibration…