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The preparation of hollow zeolite with a large cavity structure to improve the accessibility to the active sites of catalyst is of great significance. A thin-walled Ti-rich hollow Titanium silicalite-1 (TS-1) Nanobox was synthesized by dissolution-recrystallization using Silicalite-1 (S-1) as the parent zeolite and (NH 4) 2 SO 4 as the dual-function crystallization-mediating agent. The wall thickness of the zeolite is about 30 nm, the hollow percentage (the ratio of the cavity area in the middle of the zeolite to the overall area of the zeolite) can reach 0.57, and the Si/Ti ratio is 39.63. The formation mechanism of hollow TS-1 was studied. As the parent zeolite, S-1 is easier to dissolve than TS-1, making it easier for the hollow zeolite to get a complete cavity. When the molar ratio of (NH 4) 2 SO 4 /TEOS reaches 0.25, the dissolution rate matches the crystallization rate best, and a perfect hollow structure is obtained. The pH of the initial gel is the key factor for the hollow structure. The catalytic activity and stability were tested by 1-hexene epoxidation. The conversion of 1-hexene using HTS-1#S0.25 as the catalyst is much higher than that using hollow TS-1 prepared by the conventional method as the catalyst. HTS-1#S0.25 remains a high oxidation activity and high selectivity after five recycle experiments. In addition, the type of anion also has a great influence on the reactivity. This method can provide a new idea for the preparation of hollow TS-1. Two hollow structures under the action of (NH 4) 2 SO 4 (a), the mechanism of HTS-1 formation (b) and HTS-1 using (NH 4) 2 SO 4 as the crystallization-mediating agent (c). [Display omitted] • A Ti-rich TS-1 Nanobox is synthesized by dissolution-recrystallization. • pH is a key factor affecting the competition between dissolution and crystallization. • (NH 4) 2 SO 4 is the dual-functional crystallization-mediating agent. • Silicalite-1 is used as parent zeolite for the synthesis of hollow TS-1. • The material has the high activity for 1-hexene epoxidation reaction. [ABSTRACT FROM AUTHOR]

Zeolites with metal clusters encapsulated within the pore structure have attracted more attention because of their unique properties with high stability, but diffusion resistance is the bottleneck limiting the utilization efficiency of active centers, especially in macromolecular reactions. Hollow zeolites could effectively improve mass transport by reducing the wall thickness. In this work, cobalt-base hollow silicate-1 zeolite was obtained by mother liquid treatment with sodium chloride. Various characterization results show that the CoOx@HS-1-0.5Na+ crystals have completely hollow structure and small cobalt cluster highly dispersed encapsulated in it. The presence of Lewis acid sites and the unique hollow structure resulted in enhanced selectivity to benzaldehyde in the styrene oxidation. The effect of various factors including cobalt loading, the concentration of sodium ion, reaction solvents and H 2 O 2 /styrene molar ratio on the catalytic performance were systematically investigated. The yield of benzaldehyde can achieve 73.8% with 83.59% styrene conversion and 88.29% benzaldehyde selectivity. Styrene is oxidized to benzaldehyde with high selectivity under the action of Lewis acid displayed by cobalt nanoclusters in hollow zeolite channels. [Display omitted] • Cobalt clusters were successfully encapsulated in zeolite with the assistance of inorganic salts. • Cobalt based hollow zeolite rich in Lewis acid sites were successfully synthesized. • Styrene conversion and benzaldehyde selectivity are related to cobalt loading and sodium ion concentration. • CoOx@HS-1-0.5Na+ catalyst exhibit high activity and selectivity toward styrene oxidation. [ABSTRACT FROM AUTHOR]

Development of economic routes for synthesis of hollow titanium silicalite-1 (TS-1) zeolite is of great importance in industry. However, there are still challenges to synthesize hollow TS-1 zeolite without anatase TiO 2. In this work, a one-step strategy without mesoporogen by the solid-phase conversion method was successfully developed to synthesize anatase-free hollow TS-1. The appropriate low amount of TPAOH (TPA/SiO 2 = 0.13) and the suitable crystallization temperature (170 °C) can not merely induce the formation of hollow structures, but also enable more titanium to enter the framework. Moreover, the transformation mechanism based on crystallization rate and dissolution rate was proposed according to the investigation of the transformation process. The hollow TS-1 with large cavities exhibits high catalytic activity and recycle stability in 1-hexene epoxidation. The efficient strategy reported in this paper will provide new opportunities for further promoting the industrial application of hollow TS-1. [Display omitted] • Hollow TS-1 has been synthesized by the solid-phase conversion method. • No extra anatase TiO 2 exists in Hollow TS-1. • The TPAOH content and temperature are essential for the synthesis of Hollow TS-1. • The transformation mechanism based on crystallization rate and dissolution rate was proposed. [ABSTRACT FROM AUTHOR]

Hierarchical Fe-doped MFI/MCM-41 composites (Fe-HMZs) were one-pot hydrothermal synthesized by partial transformation strategy using conventional CTAB as a dual-functional template. The hierarchical Fe-doped MFI/MCM-41 composites possess ordered mesopores and crystallized MFI structure. The effect of addition amount of NaOH and CTAB as well as the type of the alkali source on the formation of hierarchical Fe-MFI/MCM-41 composites have been investigated in detail. In addition, the temperature-gradient treatment plays the vital roles in the formation of MFI and the possible formation mechanism has been proposed. The obtained hierarchical Fe-HMZ-40 sample exhibits outstanding catalytic performance for phenol hydroxylation and 48% of phenol conversion as well as 89% of dihydroxybenzene selectivity could be achieved, which are ascribed to the more accessible active sites endowed by the significant diffusion ability of ordered mesopores. Compared with Fe-MCM-41 sample, the hydrothermal stability is improved because of the presence of MFI structure. Hierarchical Fe-doped MFI/MCM-41 composites (Fe-HMZs) were one-pot hydrothermal synthesized by partial transformation strategy using conventional CTAB as a dual-functional template. [Display omitted] • Hierarchical Fe-MFI/MCM-41 composites were one-pot hydrothermal synthesized. • The conventional CTAB is used as a dual-functional template. • The synthesized composite has ordered mesoporous and MFI simultaneously. • The partial transformation method is effective in the synthesis of MFI using CTAB. • The composite shows the superior catalytic performance in hydroxylation of phenol. [ABSTRACT FROM AUTHOR]

It is of great significance to develop a novel strategy to synthesize hollow zeolite without using mesoporogens due to its extremely short diffusion length. Ferric nitrate as a common iron source and structure direction agent has been used for synthesizing Fe-doped zeolite. However, the effect of ferric nitrate on the morphology of zeolite has not yet been elaborated. Here, we successfully synthesized hollow MFI zeolite with a framework iron-rich surface by using ferric nitrate as an iron source and seed-assistant strategy. It is the first time to propose that inorganic iron has the hollow structure-directing effect. Herein, by comparatively investigated the effect of iron content on the structure and evolution process of hollow zeolite, a novel crystallization mechanism has been proposed based on the competitive relationship between crystallization and dissolution rates. When the Si/Fe ratio reaches 25, the internal dissolution rate of seeds is faster than the surface crystallization rate of zeolite, the hollow structures are acquired. The obtained Fe-doped hollow zeolite exhibits superior catalytic performance for the reaction of phenol degradation. In this reaction, the higher effectiveness factor (η) close to 1 of Fe-doped hollow zeolite confirmed by calculations indicates its superior mass transferability. [Display omitted] • Hollow MFI zeolite with Fe-rich surface was synthesized by using Fe(NO 3) 3 and seed. • Ferric nitrate as a direct agent of hollow zeolite has been confirmed. • A mechanism was proved namely competition between crystallization and dissolution. • High content Fe (Si/Fe ratio = 25) is conducive to the formation of hollow zeolite. • Hollow Fe-MFI zeolite shows a superior catalytic activity for phenol degradation. [ABSTRACT FROM AUTHOR]

In recent years, using waste iron ore tailings (IOT) as a starting material to synthesize new materials has become an emerging hot topic, but the remaining challenge is the lack of effective ways to maximize the use of each component in the IOT. In this work, two novel materials including the mesoporous zincsilite composite assembled by a layered structure with flower-like morphology and the willemite composite composed of ellipsoidal particles were synthesized from high-silicon IOT via a facile one-step hydrothermal reaction process. Due to the transformation from IOT to zincsilite composite, typical mesoporous structure was formed and the specific surface area was increased by 75.1 m2 g−1. The transformation mechanisms from IOT to zinc silicate composites were proposed based on the study of the synthesis process. The zincsilite composite shows fast adsorption rate and high adsorption capacity for MB, which is mainly attributed to the emerging mesopores and special layered structure. Specifically, the removal efficiency for methylene blue exceeds 97% within 10 min, and the maximum adsorption capacity reaches up to 180.5 mg g−1, which is over 9 times higher than that of raw IOT. Furthermore, analysis of adsorption mechanism demonstrated that the adsorption process was mainly caused by the synergistic effect of both hydrogen bonding and electrostatic attraction. The excellent adsorption property endows the composite with potential application in the field of dye wastewater treatment. Image 1 • A facile functional utilization strategy of iron ore tailings (IOT) was proposed. • Mesoporous zinc silicate composite was prepared by one-step hydrothermal reaction. • IOT as an industrial waste was used as a low-cost silicon source in the preparation. • The structure and morphology evolution of zinc silicate composite was explored. • Zincsilite composite showed fast rate and high capacity for adsorption of dye. [ABSTRACT FROM AUTHOR]