Heterogeneous Catalyst Characteristics of TiO2 Nanoparticles Impregnated with Alkaline CH3ONa for Use in Transesterification Process

Abstract

A strong alkaline catalyst, sodium methoxide (CH3ONa), is commonly used to catalyze the transesterification reaction for biodiesel production. Meanwhile, titanium dioxide (TiO2) anatase with a bandgap of 3.2 eV is a highly competitive photocatalyst after the absorption of sufficient energy from ultraviolet light. There has been no published report on the synergistic catalyst effects of CH3ONa and TiO2 on further facilitating the transesterification reaction. Hence, an impregnating method was used in this study to prepare the heterogeneous photocatalyst comprising TiO2 nanoparticles embedded with a CH3ONa catalyst. The TiO2 nanoparticles were first immersed in an aqueous solution of CH3ONa so that CH3ONa could diffuse into the interior surfaces of the TiO2 porous structure. The mixture of TiO2 and CH3ONa was then calcined in the temperature range from 150 °C to 450 °C for 4 h to produce the TiO2/CH3ONa photocatalyst. Various characteristics of the catalyst were analyzed to determine the optimum preparation conditions. The Fourier transform infrared spectroscopy spectra revealed that the absorption peaks of CH3ONa appeared in the wavelength range of 600 cm−1 and 1500 cm−1. The X-ray diffractometer analysis showed that the calcined CH3ONa did not alter the crystal structure of the catalyst carrier TiO2. At the calcined temperatures between 100 °C and 800 °C, no intermediate or pyrolyzed product of CH3ONa was detected, as revealed by the thermogravimetric analyzer spectra. In addition, about 5~9 wt.% elemental calcium in the CH3ONa solution could be calcined onto the surface of TiO2. In addition, the FTIR spectra confirmed the successful sintering and bonding of CH3ONa onto the TiO2 nanoparticles. The energy dispersive spectrometry result revealed that the interior surface of the TiO2 nanoparticles was filled with the CH3ONa compound.