Abstract
Niobic acid,Nb2O5⋅nH2O, has been supported on the titanium silicalite by impregnation method. The obtained materials were characterized by X-ray diffraction, infrared, and ultra-violet—visible diffuse reflectance spectroscopy, temperature programmed reduction, pyridine adsorption, and field emission scanning electron microscopy techniques. It was demonstrated that the tetrahedral titanium species still retained after impregnation of niobic acid. The results revealed that niobium species interacted with hydroxyl groups on the surface of TS-1. The niobium species in the catalysts are predominantly polymerized niobium oxides species or bulk niobium oxide with the octahedral structure. All catalysts showed both Brønsted and Lewis acid sites. The catalysts have been tested for epoxidation of 1-octene with aqueous hydrogen peroxide. It was found that the presence of niobic acid in the catalysts enhanced the rate of the formation of epoxide at the initial reaction time. Diol as a side product was also observed due to the acidic properties of the catalysts.
Highlights
Niobium oxides and its compounds are interesting and important materials in catalysis with various functions such as promoter, support, redox materials, and acid catalysts [1,2,3]
We have reported recently in the preliminary study that the surface hydroxyl groups in the titanium silicalite (TS-1) have bounded with niobium species in the Nb2O5/TS-1 catalyst [18]
This paper reported in detail of preparation, characterization and catalytic performance of niobic acid supported on TS-1, NBA/TS-1
Summary
Niobium oxides and its compounds are interesting and important materials in catalysis with various functions such as promoter, support, redox materials, and acid catalysts [1,2,3]. For the infrared spectra of samples XNb/TS-1, a small band at around 970 cm−1 characteristic for titanium ions in the tetrahedral structure is still present after impregnation of niobium. Sample NBA prepared by hydrolysis of niobium ethoxide and calcined at 200◦C, exhibited three regions of hydrogen consumption, that is, a negative peak at around 550◦C and the high positive peaks at around 900◦C and at a higher temperature above 1000◦C.
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