Synthesis of Hierarchical Titanium‐Rich Titanium Silicalite‐1 Zeolites and the Highly Efficient Catalytic Performance for Hydroxylation of Phenol

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.

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

“…This procedure usually involves the use of hard or soft templates ( e. g . surfactants, polymer beads, carbon nanotubes, carbon black) [165–169] . Also, Moreno and co‐workers proposed to prepare hierarchical TS‐1 (see Figure 4e) via the functionalization of zeolite seeds (pre‐formed in a liquid gel or in an amorphous Ti−SiO 2 xerogel) with organosilanes prior to the crystallization step [152,170] .…”

Tetrapropylammonium Hydroxide Treatment of Aged Dry Gel to Make Hierarchical TS-1 Zeolites for Catalysis

“…The Ti coordinate states in the four samples were also studied by FT-IR (Figure d). The absorption peak at 960 cm –1 is due to the vibration of the Si–O–Ti bond or the vibration of Si–O–Si closely connected with Ti–O–Si, while the absorption peak at 800 cm –1 is attributed to the characteristic peak of the MFI topology. , The relative intensity ratio of the two peaks at 960 and 800 cm –1 ( I 960/800 ) can be used to assess the content of framework Ti species in the zeolitic frameworks; i.e., a relatively large value of I 960/800 suggests more framework Ti species in the framework. , As shown in Figure d, the I 960/800 values of these samples rank as HTS-0.1-1.0-9H > CTS-0.1-1.0-9H > CTS-1 > NTS-1, which confirms the findings by UV–vis. In addition, 29 Si NMR spectroscopy in Figure S2 also proved the high framework content Ti species in HTS-0.1-1.0-9H.…”

“…30,31 The relative intensity ratio of the two peaks at 960 and 800 cm −1 (I 960/800 ) can be used to assess the content of framework Ti species in the zeolitic frameworks; i.e., a relatively large value of I 960/800 suggests more framework Ti species in the framework. 32,33 As shown in Figure 2d, the I 960/800 values of these samples rank as HTS-0.1-1.0-9H > CTS-0.1-1.0-9H > CTS-1 > NTS-1, which confirms the findings by UV−vis. In addition, 29 Si NMR spectroscopy in Figure S2 also proved the high framework content Ti species in HTS-0.1-1.0-9H.…”

Investigation on Titanium Silicalite-1 Zeolite Synthesis Employing ATPAOH as an Organic Structure Directing Agent

“…This function has recently been found and applied in the synthesis of aluminum-containing zeolites such as ZSM-5, H-MOR, MCM-22, etc. − The strong interaction between OSDAs and the inorganic host is studied, and it inspires efforts to tailor the framework Al by optimizing OSDAs . The distribution of Ti species within the matrix is also crucial for TS-1 zeolite, as its content, − coordination states, − as well as accessibility − determines the catalytic performance of TS-1 zeolite. Several strategies , have been developed to adjust the distribution of heteroatoms in the zeolite skeleton.…”