Synthesis of two-dimensional TiO2@multi-walled carbon nanotube nanocomposites as smart nanocatalyst for ultra-deep oxidative desulfurization of liquid fuel: Optimization via response surface methodology

Abstract

The novel heterogeneous catalysts of 2D-TiO2@MWCNT nanocomposites are designed and synthesized via grafting TiO2 nanoparticles onto functionalized multi-walled carbon nanotubes and used for oxidative desulfurization of dibenzothiophene and real straight run light gas oil. The 2D-TiO2@MWCNT nanocomposite catalysts are completely characterized by FT-IR, Raman spectroscopy, XRD, TEM, NH3-TPD, ICP, and N2 adsorption–desorption isotherms. At first, the effect of various loading Ti on the MWCNT for ODS efficiency was investigated. The results revealed that 2D-0.6TiO2@MWCNT had the highest sulfur removal for the model, and SRLGO fuel compared to the other catalyst. Then, the optimal design of experiments using Box–Behnken experimental design was used to evaluate the effects of individual process variables such as temperature, O/S molar ratio, time, catalyst dosage, and their optimum values were found to be 69 °C, 46 min−1, O/S molar ratio: 9, and 0.03 g cat (25 ml DBT model fuel with 500 ppm S or 25 ml SRLGO with 12500 ppm S, 25 ml of acetonitrile), to achieve a high removal sulfur efficiency for DBT model oil (100%) and SRLGO (97.5 %), respectively. Based on optimal conditions, the 2D-0.6TiO2@MWCNT catalyst possesses superior catalytic activity and excellent reusability. The desulfurization reaction could be recycled for at least nine cycles without considerable reduction of catalytic performance, showing the good stability of the nanocomposite catalysts. An empirical kinetic model was applied to explain the rate data. Also, 2D-0.6TiO2@MWCNT nanocomposite catalyst had the lowest activation energy (27.65 Kj.mol−1) with the highest turnover frequency (16.15 h−1, around 2–3 times of the best catalyst so far) in desulfurization reactions compared to any TiO2-based catalysts. Furthermore, the catalytic reaction mechanism is investigated.