Synthesis of titanium-rich boron-free MWW-type zeolites by acid-assisted post-synthesis treatment of small-size pure-silica precursors for alkene epoxidation

IF 4.7 3区材料科学 Q1 CHEMISTRY, APPLIED

Microporous and Mesoporous Materials Pub Date : 2025-08-28 DOI:10.1016/j.micromeso.2025.113835

Jiamei Wang , Kairui Fu , Wenjian Yu , Shuai Wang , Yuji Gao , Guangqiang Lv , Takashi Tatsumi , Jingui Wang

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引用次数: 0

Abstract

Titanium-containing zeolites have attracted much attention because their framework titanium species as Lewis acid sites can activate green oxidants of hydrogen peroxide. This unique property enables their application in environmentally-benign oxidation processes. Among them, titanium-containing MWW-type zeolites with a unique layered structure have attracted great attention. The direct hydrothermal synthesis of Ti-MWW zeolites usually requires boric acid as an auxiliary crystallization agent. This boric acid-assisted method had adverse influence on the microenvironment of Ti active sites. The synthesis of boron-free and titanium-rich Ti-MWW remains very meaningful and challenging. Here, an effective strategy was reported to prepare titanium-rich, boron-free Ti-MWW zeolite catalysts by using low-volatility and stable Ti(SO₄)₂/H₂SO₄ acid solution to post-treat uncalcined pure-silica MWW-type zeolitic precursors (so-called ITQ-1 precursors). This strategy can effectively suppress the formation of extra-framework titanium species, which is usually formed in the Ti-MWW zeolites synthesized by traditional methods. In addition, the introduction of titanium species can be controlled by altering the structure and morphology of the precursors. It was proven that reducing the size of ITQ-1 precursors by increasing the rotation speeds during synthetic processes could promote the content of inserted Ti species by post-synthesis treatment. Ti-MWW zeolites with a more than 3.7 mol.% Ti content were achieved, most of which were tetrahedrally-coordinated framework titanium species composed of both closed-site and open-site titanium species. As far as we know, this content was the highest amounts to introduce titanium species into pure-silica ITQ-1 precursors. Due to the high content of framework Ti species, Ti-MWW catalyst showed high catalytic performance in alkene epoxidation.

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烯环氧化小粒径纯硅前驱体酸助后处理合成富钛无硼mww型沸石

含钛沸石由于其骨架钛作为路易斯酸位点可以激活过氧化氢的绿色氧化剂而受到广泛关注。这种独特的特性使其能够应用于环境友好的氧化过程。其中，具有独特层状结构的含钛mww型沸石备受关注。水热法直接合成Ti-MWW沸石通常需要硼酸作为辅助结晶剂。硼酸辅助法对钛活性位点的微环境有不利影响。无硼富钛钛钨的合成仍具有重要的意义和挑战性。本文采用低挥发性稳定的Ti(SO4)2/H2SO4酸溶液对未煅烧的纯二氧化硅mww型沸石前驱体（ITQ-1前驱体）进行后处理，制备了富钛、无硼的Ti- mww分子筛催化剂。该策略可以有效抑制传统方法合成的Ti-MWW分子筛中通常形成的框架外钛的形成。此外，钛的引入可以通过改变前驱体的结构和形态来控制。结果表明，在合成过程中，通过提高ITQ-1前驱体的旋转速度来减小ITQ-1前驱体的尺寸，可以通过合成后处理提高插入Ti的含量。钛含量大于3.7 mol.%的Ti- mww分子筛，大部分为由闭位和开位钛组成的四面体配位骨架钛种。据我们所知，该含量是纯硅ITQ-1前驱体中引入钛种的最高含量。Ti- mww催化剂由于骨架Ti组分含量高，在烯烃环氧化反应中表现出较高的催化性能。

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来源期刊

Microporous and Mesoporous Materials 化学-材料科学：综合

CiteScore

10.70

自引率

5.80%

发文量

649

审稿时长

26 days

期刊介绍： Microporous and Mesoporous Materials covers novel and significant aspects of porous solids classified as either microporous (pore size up to 2 nm) or mesoporous (pore size 2 to 50 nm). The porosity should have a specific impact on the material properties or application. Typical examples are zeolites and zeolite-like materials, pillared materials, clathrasils and clathrates, carbon molecular sieves, ordered mesoporous materials, organic/inorganic porous hybrid materials, or porous metal oxides. Both natural and synthetic porous materials are within the scope of the journal. Topics which are particularly of interest include: All aspects of natural microporous and mesoporous solids The synthesis of crystalline or amorphous porous materials The physico-chemical characterization of microporous and mesoporous solids, especially spectroscopic and microscopic The modification of microporous and mesoporous solids, for example by ion exchange or solid-state reactions All topics related to diffusion of mobile species in the pores of microporous and mesoporous materials Adsorption (and other separation techniques) using microporous or mesoporous adsorbents Catalysis by microporous and mesoporous materials Host/guest interactions Theoretical chemistry and modelling of host/guest interactions All topics related to the application of microporous and mesoporous materials in industrial catalysis, separation technology, environmental protection, electrochemistry, membranes, sensors, optical devices, etc.