Studies On Preparation Of Nb Modified Oxides/Mesoporous Molecular Sieves And Their Catalytic Activities For Several Reactions

To be a new kind of catalytic materials, niobium compound has aroused extensive concern in the domestic and international academics due to its unique structure and excellent properties. They can be used as a catalyst of the active component, promoter or carrier, Niobic acid and compounds containing niobium are applied in a wide range of catalysis fields for their unique acidic property, oxidizing and thermal stability. Such as:dehydration, dehydrogenation, hydration, hydrolysis, epoxidation, ammoxidation, hydroisomerization, esterification, alkylation, condensation, disproportionation, desulfurization, denitrification, photocatalytic reactions and so on. China boasts abundant niobium mineral resources for the development of niobium industry with the advantaged superiority. However, currently the research of theoretical basis, analytical methods, development and application prospects about niobium-based compounds is still at the starting stage. So, It has an important theoretical referenced value and practical significance to explore the catalytic systems of high efficient, clean and green.In this study, using NbCls as precursor, three kinds of Nb-based catalyst were prepared. There are Nb/Ti-MCM-41, Nb-MCM-41 and (Nb, I, N) doped TiO2, which synthesized by precursor method, hydrothermal method and sol-gel method, respectively. The samples were characterized by XRD, N2 adsorption-desorption, FT-IR, UV-vis, TG, XPS and the reasons of formation also discussed. The catalytic activity of as-prepared samples were evaluated in the photodegradation of methylene blue under UV-light, hydroxylating phenol reaction, and the visible-light photodegradation of Azithromycin pharmaceutical wastewater, respectively.The X-ray diffraction patterns indicate that the modified materials (Nb/Ti-MCM-41 and Nb-MCM-41) retain the standard MCM-41 structure. The Nb deposited into the structure of Ti-MCM-41. Whereas, to Nb-MCM-41, the Nb atoms are present in the framework instead. XPS study shows that the dopants (Nb, I, N) have been doped into the bulk of TiO2.Nb/Ti-MCM-41 shows a significant MB elimination efficiency under UV light, duo to its porosity, huge specific surface area and the promoting effect of niobium dispersed into the structure. During a 3-hour reaction, Nb/MCM-41 demonstrates the best adsorption and photocatalytic activity (83% of MB decolored at the dark adsorption) as compared with other samples.The catalytic activity of Nb-MCM-41 toward hydroxylation of phenol in aqueous medium was evaluated using H2O2 as the oxidant at 80℃.The effects of reaction parameters such as Si/Nb ratios, temperature, catalyst amount, and time were also investigated. The results show that the optimal reaction condition is a 100 mg L-1 catalyst dosage, Si/Nb=48, reaction temperature of 55℃and a 6-h reaction time. the Nb-MCM-41-48 showes nearly 96% benzenediol selectivity and high CAT/HQ ratio, to 80 times.The XRD patterns reveal that the mono-doped samples display only anatase phase, whereas the codoped I-N-TiO2 exhibits a mixed-phase (anatase and rutile phase). All the doped TiO2 were applied in the treatment of Azithromycin pharmaceutical wastewater(APW), and they demonstrates different activity for the photocatalytic treatment of APW under visible light. After a 12-hour reaction, I-N-TiO2 demonstrated the best photocatalytic activity of APW (57% APW degradation percentage). On the contrary, the wost one the Nb-TiO2, with the only 2.7% APW degradation percentage.