No abstract

Improving the framework titanium (Ti) of titanium silicalite-1 (TS-1) zeolites and creating inter-crystalline mesoporosity are two ways to enhance the catalytic properties of TS-1 for hydroxylation of phenol. Most researches only used one of the ways. In this study, we successfully synthesized of hierarchical Titanium-Rich (Ti-rich) TS-1. Ti-rich TS-1 was synthesized in the presence of ammonium carbonate ((NH 4 ) 2 CO 3 ). The framework Ti content of TS-1 zeolites synthesized by different content of (NH 4 ) 2 CO 3 was studied by X-ray fluorescence (XRF), Fourier transform infrared spectra (FTIR) and ultraviolet visible spectra, the framework Ti content was significantly increased by using (NH 4 ) 2 CO 3 as crystallization-mediating agent. The synthesized samples were evaluated in hydroxylation of phenol. When the molar ratio of ammonium carbonate and tetraethyl orthosilicate in the synthesis gel was 0.2, the molar ratio of Si/Ti reached 34.43 and the Ti-rich TS-1 shows the optimum catalytic activity in hydroxylation of phenol. The post-modification with aqueous solution of tetrapropylammonium hydroxide (TPAOH) was used to further improve the diffusion property. Compared with the parent TS-1, the secondary pore volume was all increased. The developed hierarchical Ti-rich TS-1 zeolites were also assessed in hydroxylation of phenol. It was confirmed that hierarchical Ti-rich titanium silicalite-1 zeolites can improve the catalytic activity in phenol conversion considerably.

Hierarchical ZSM-5 zeolites of controlled porous structure were realized by the cooperative direction of organosilanes and tetrapropylammonium hydroxide.

BACKGROUND ZSM‐5 zeolites are of great importance in industrial catalysis. However, the diffusion limitations caused by small pore opening restrict the extent of catalytic conversions over conventional ZSM‐5. Many studies have shown that mass transfer in zeolite channels can be improved by controlling the morphology or creating additional mesoporosity. Here, the catalytic performance is further improved by the creation of hollow structure and intracrystalline mesopores in ZSM‐5 zeolite. RESULTS The characterization results demonstrated that hollow ZSM‐5 with intracrystalline mesopores can be synthesized by using a simple one‐step hydrothermal strategy with a commercial gemini‐type cationic surfactant containing hydrophilic hydroxyl groups. Compared with the Fe‐substituted conventional ZSM‐5, the Fe‐substituted hollow ZSM‐5 with intracrystalline mesopores show remarkably enhanced catalytic performance in the hydroxylation of phenol. About 52.2% conversion of phenol can be obtained with almost 96.8% selectivity to dihydroxybenzenes. The catalytic activity remained almost unchanged after five cycles. CONCLUSION The newly created hollow structure and intracrystalline mesopores in ZSM‐5 zeolite showed enhanced catalytic activity and reusability for the hydroxylation of phenol, which is higher than most reported systems. The prepared catalyst is a promising alternative material for the hydroxylation of phenol. © 2017 Society of Chemical Industry