Phosphotungstic Acid Supported on Rice Husk Ash Catalyzed Synthesis of n-Butyl Acetate

Rice husk is a byproduct of rice milling, containing a high percentage of silica (silicon dioxide). Rice husk ash (RHA), produced from rice husk, was used as a support for 12-phosphotungstic acid. It is a practical and potentially beneficial approach in catalysis. A series of supported catalysts with 12-phosphotungstic acid (20–40 wt % of H₃PW₁₂O₄₀), immobilized on rice husk ash via impregnation using the initial moisture content method, were prepared. The catalysts were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis and scanning electron microscopy (SEM) for annotation of the catalytic behavior. The catalytic activity of the H₃PW₁₂O₄₀/RHA catalyst was evaluated in the synthesis of n-butyl acetate. The catalyst with 30 wt % H₃PW₁₂O₄₀, immobilized on rice husk ash, demonstrated the highest conversion of acetic acid. The reactions were carried out in a batch reactor. The highest conversion of 84.2% was attained under optimal conditions: temperature of 120°C, an acid-to-alcohol mole ratio of 1 : 2, agitation at 400 rpm, and catalyst loading of 1.5 wt % over 180 min. Additionally, the catalyst was also assessed to determine its stability and reusability.