Mesostructured technische universiteit delft-1 and technische universiteit delft-crystalline supported metal oxide doped titania as photocatalyst and oxidative catalyst

Abstract

This research focused on the development of new Technische Universiteit Delft (TUD)-supported catalysts that are applicable for the photodegradation of organic pollutants and for the epoxidation of various olefins. In this study, the feasibility of relatively new mesoporous materials namely Technische Universiteit Delft-1 (TUD-1), amorphous silica material and Technische Universiteit Delft- Crystalline (TUD-C), hierarchical zeolitic material with MFI framework as the support for transition metal oxide doped titania was investigated. Two series of samples TUD-1 supported Cr doped TiO2 (Cr-TiO2/TUD-1(x)) and TUD-C supported Mo doped TiO2 (Mo-TiO2/TUD-C(y)) were synthesized via a single softtemplating approach involving the combination of sol-gel and hydrothermal treatment. The synthesized materials were characterized using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Diffused Reflectance Ultraviolet-visible Spectroscopy (DRUV-Vis), Nitrogen adsorption-desorption surface analysis, Temperature Programmed Desorption of Ammonia analysis (NH3- TPD), X-ray Photoelectron Spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). Optimization was carried out by varying the Si/Ti molar ratio in TUD-1 (x = 10 – 50) and Si/Al molar ratio in TUD-C (y = 10 – 50). For the photocatalytic reactions, results demonstrated that all the TUD-1 supported Cr-TiO2 materials were better photocatalysts compared to that of unsupported Cr-TiO2. Cr-TiO2/TUD-1(30) achieved the highest photodegradation percentage for Malachite Green (75.6%), Congo Red (50.8%) and phenol (82.0%) under visible light irradiation. The adsorption of phenol followed the Langmuir adsorption isotherm, while the photodegradation of phenol obeyed the first order kinetics. As for the oxidative reactions, Mo-TiO2 supported on TUD-C, with Si/Al molar ratio = 10 exhibited the highest epoxide yield for various types of olefins at ambient conditions. As compared to the unsupported Mo-TiO2, TUD-C supported Mo-TiO2 samples showed significantly higher conversion with 100% selectivity towards formation of epoxides. All the epoxidation reactions followed the first order kinetics. The increment of catalytic activities for both series of materials is attributed to the high surface area (496 – 1034 m2/g) and tunable porosity (2.83 – 5.84 nm), which provides better adsorption and diffusivity. The excellent oxidative capabilities of TUD-C supported materials were also accounted for the increased acidity originated from the aluminosilicate framework. Effect of reaction parameters including initial concentration (100 - 500 ppm), pH (2 - 11), catalyst amount (0.05 - 0.5 g), and reaction duration (6 - 72 h) in both photocatalytic and oxidative reactions were studied. TUD-1 and TUD-C are promising catalyst supports and have significantly improved the photocatalytic and catalytic performance of the transition metal oxides doped TiO2.