Regeneration of Simulated Deactivated Hollow Titanium Silicate Zeolite by Secondary Crystallization in the TPAOH Solution

摘要

It is of paramount importance to improve the utilization efficiency of hollow titanium silicate(HTS) zeolite catalyst used in the cyclohexanone ammoxidation process. To achieve this aim, the regeneration of simulated deactivated HTS zeolite by post-synthesis was carried out in an aqueous TPAOH solution under hydrothermal conditions. It was found that the catalytic performance for phenol hydroxylation over regenerated HTS zeolite was as high as that of fresh one.Judging from the BET measurements, electron micrography and XRD analysis results, it was confirmed that the topological and morphological structure was repaired. The chemical state of Ti species was detected by the UV-Vis and ^(29)Si MAS NMR spectroscopy. No acidic amorphous TiO_2-SiO_2 oxide was formed, and the extraframework Ti species could be reincorporated into the framework of HTS zeolite thanks to the tetrahedral coordination by the condensation between Ti-OH and Si-OH groups. In order to confirm this conclusion, the fresh HTS zeolite was treated under the NH_3·H_2O hydrothermal and thermal conditions for several times. The catalytic activity of both uncalcined and calcined simulated deactivated HTS zeolite samples could be regenerated without the formation of Br?nsted acid sites. It was concluded that the highly dispersed Ti species could be reincorporated into the framework of zeolite by hydrated condensation of Si-OH and Ti-OH groups after secondary hydrothermal synthesis.