Nitrogen-incorporated TS-1 zeolite: Synthesis, characterization and application in the epoxidation of propylene

A novel nitrogen-incorporated TS-1 zeolite (N-TS-1) was successfully synthesized by direct calcinating the as-synthesized TS-1 powder in NH3 flow at high temperature. The samples were characterized by XRD, FTIR, UV–Vis, NH3-TPD, ICP-AES, CHN, XPS and 29Si MAS NMR techniques. The results showed that nitrogen was incorporated into the framework of TS-1, and N-TS-1 preserved the MFI structure well. The fresh N-TS-1 samples showed low H2O2 conversion in the epoxidation of propylene with dilute H2O2, which was due to the coverage of the active titanium sites by unstable nitrogen species. By refluxing the fresh N-TS-1 samples with methanol, the unstable nitrogen species were washed out and the conversion of H2O2 increased markedly. The stable nitrogen species incorporated into the zeolite framework could effectively decrease the acidity of TS-1 zeolite and inhibit the side reactions, thereby improving the propylene oxide (PO) selectivity. After the 20th run, the N-TS-1-850-5 catalyst gave a H2O2 conversion of 91.5%, a H2O2 selectivity of 92.0%, and a PO selectivity of 90.9%. Finally, a model for nitridation of the as-synthesized TS-1 powder at high temperature was proposed.

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► Nitrogen-incorporated TS-1 was prepared by nitridation of the as-synthesized powder.
► The incorporation of N species in the framework of TS-1 can adjust its acidity.
► The N-TS-1 showed high selectivity and stability for propylene epoxidation.