Stability assessment of na-doped mesoporous gamma alumina catalyst in transesterification reaction

Abstract

The leaching of active species was reported to have been the major problem among alkali doped heterogeneous catalysts. Modifying the structure and texture of catalyst support can improve the catalyst’s stability and its activity. In this study, mesoporous gamma alumina, with exellent textural properties, was modified using different amount of NaOH by wet impregnation method, and the catalyst's stability evaluated. The catalysts were characterized using Fourier Transform Infra-Red (FTIR) spectroscopy, N₂-sorption (BET), Basic Back Titration, Field Emission Scanning Electron Microscopy (FESEM), and X-Ray Fluorescence (XRF) spectroscopy. There was increased in the number of basic sites and decreased in surface area with increased in the amount of NaOH doping. The FESEM image indicated the incorporation of Na into the alumina after modification. The catalysts were employed in the methanolysis of corn oil, and the biodiesel product analyzed using Proton Nuclear Magnetic Resonance (¹H NMR) and Fourier Transform Infra-Red/Attenuated Total Reflection (FTIR-ATR) analyses. The reaction conditions for the methanolysis were catalyst loading (5 wt%), oil:methanol molar ratio (1:15), temperature (65 °C) and reaction time (3 h). Highest biodiesel yield of 98.9% was obtained in the present of 15% Na/Al₂O₃ catalyst. From the leaching test, the catalyst was found to be relatively stable, as only 0.7% of Na₂O was leached out. The lixiviation study further buttresses this assertion, with only about 13.5% yield, ruling out any considerable homogeneous contribution in catalytic activity.