Electrosynthesis of copper oxide supported on amorphous titanum dioxide nanoparticles based catalysts for photocatalytic oxidative desulfurization

Abstract

The high level of sulfur in fuel has contributed to the emission of sulfur oxide (SOx) which is a major cause of air pollution, acid rain and global warming. Among desulfurization techniques, photocatalytic oxidative desulfurization (PODS) has received much attention due to low energy consumption, high efficiency and ability to convert toxic organic pollutants into non-toxic products. Coupling of the widely used titanium dioxide (TiO2) photocatalyst with other semiconductor oxides can produce superior catalyst with a good interaction, appropriate amount of defects and narrower band gap for efficient photoactivity. Amorphous TiO2 has experienced intensive advances due to larger surface area, high amount of surface defects, as well as easy preparation method. In this study, copper oxide supported on amorphous titanium dioxide (CuO/TiO2) catalysts were prepared via the electrochemical method. The catalysts were characterized using x-ray diffraction, Fourier transform infrared, nitrogen adsorption-desorption, transmission electron microscopy, x-ray photoelectron spectroscopy, electron spin resonance and ultraviolet-visible diffuse reflectance spectroscopy. The effects of using titanium (IV) isopropoxide (TTIP) or titanium (IV) butoxide (TBOT) for synthesizing the amorphous TiO2 (AT) and different copper (Cu) loading (5-20 wt%) were investigated on PODS of dibenzothiophene (DBT). ATTBOT showed a higher photoactivity than ATTTIP due to the presence of larger pore diameter and pore volume for adsorption of more DBT molecules, thus enhancing the activity. The loading of 5-20 wt% CuO onto ATTBOT (CATTBOT) further increased the activity due to the narrow band gap and the presence of Ti-O-C, O-Ti-C, O-Ti-N and Ti-O-Cu bonds that play a role as electron acceptor and transporter. Among all the catalysts, 15 wt% CuO/ATTTIP (15 CATTTIP) showed the best photooxidation percentage of 51.2%, due to the lower band gap, suitable amount of defects, the existence of high amount of Ti-O-Cu and Ti-O-N/O-Ti-N bonds, as well as synergistic effect between Cu and N. Optimization using the Response Surface Methodology gave the best PODS of DBT at the optimum conditions of 100 mg L-1 using 0.8 g L-1 of 15 CATTTIP that was reasonably close to the predicted value. The high PODS using 15 CATTTIP during reusability study and application on simulated oil indicate the potential of the catalyst for sulfur removal in industry.