TS-1 was synthesized by an aerosol-assisted method. SiO2–TiO2 amorphous powder was prepared by an aerosol process from an aqueous solution of silicon and titanium sources under acid conditions, which can make titanium ions highly distributed without complex operations. The powder was crystallized with a given amount of template agent (25% TPAOH) under autogenous pressure. Without adding extra water, the crystallization system maintained a high concentration of template agent, which can significantly reduce the amount of template and the discharge of polluted water. TS-1 with different Si/Ti ratios and different crystallization times were synthesized from the SiO2–TiO2 amorphous powder by the aerosol-assisted method. The structure, composition and morphology of TS-1 were characterized by X-ray diffraction, UV-vis spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray fluorescence spectrometry (XRF) and electron microscopy. The crystallization mechanism of TS-1 has been studied at different crystallization times. The results indicated that the crystallization process followed a liquid-phase mechanism. The incorporation of the Ti species into the framework was delayed as compared to that of the Si species. Furthermore, TS-1 exhibited good catalytic performance in propylene epoxidation with hydrogen peroxide.

This study investigated the roles of the different titanium species of low-cost TS-1 in propylene epoxidation and the influence of acid treatments. The low-cost TS-1 zeolites with different titanium species were synthesized using the hydrothermal method and characterized by ultraviolet (UV)-Raman, X-Ray Diffraction (XRD), ultraviolet visible diffuse reflectance spectroscopy (UV-Vis), N2 physical absorption and NH3 temperature programmed desorption (NH3-TPD) techniques. The roles of the different titanium species in the low-cost TS-1 samples were investigated by gas chromatography-Raman spectrometry (GC-Raman) during the propylene epoxidation process. The framework titanium species was found to be active for propylene epoxidation, while the extra-framework Ti species were found to be harmful for propylene epoxidation due to their acidity. The extra-framework Ti species can be removed by acid treatments. It was found that the acid treatment of the as-synthesized TS-1 is more effective since the amorphous TiO2 was not transformed into anatase TiO2 upon calcination. Strong acids, such as HCl, HNO3 and H2SO4, are more efficient for the elimination of the extra-framework TiO2, but do not significantly affect the framework titanium species. After treatment with an acid of a suitable concentration, the amount of the active intermediate species Ti–OOH(η2) can be increased, and a higher conversion of propylene and yield of PO can be achieved.

•Nano-sized zeolite Beta was synthesized in an extremely dense system by aerosol-assisted method.•The high concentration system accelerates the rate of nucleation and crystal growth and improves the utilization of the autoclave volume.•The crystallization process of zeolite Beta mainly followed the liquid-phase mechanism.Nano-sized zeolite Beta aggregates with interparticle mesopores were synthesized by the aerosol-assisted method. The amorphous powders in the Na2O–Al2O3−SiO2 system, which was obtained from an aerosol drying process, were used as the precursor. The zeolite was crystallized in a high concentration system with high alkalinity. This can not only improve the autoclave utilization and the crystallization rate, but also reduce the amount of both template and waste water. The obtained zeolite Beta is spherical nano-aggregates with interparticle mesopores. It shows high BET surface area and good Al species distribution. The study on crystallization process indicated that the precursor gradually dissolved under the strong alkaline condition and the nano-sized zeolite crystals were formed in the liquid phase as time prolonged. Therefore, the transformation mechanism mainly followed the liquid-phase mechanism. More importantly, the zeolite beta synthesized by aerosol-assisted method exhibited good catalytic activity and stability in the cracking reaction of 1,3,5-TIPB.An aerosol-assisted method is used to synthesize the nanosized Zeolite Beta aggregates in a extremely dense system without the addition of seeds.Download high-res image (263KB)Download full-size image

Titanium silicalite (TS-1) zeolites with different titanium species were synthesized and characterized by ultraviolet (UV)-Raman, ultraviolet visible (UV-Vis) diffuse reflectance spectroscopies and by the NH3 temperature programmed desorption (NH3-TPD) method. The roles of different titanium species in TS-1 samples have been investigated by gas chromatography-Raman spectrometry (GC-Raman) during the propylene epoxidation process. For the first time, a positive correlation was found among the concentration of framework Ti species, the amount of active intermediate Ti–OOH (η2) and the conversion of propylene by the in situ GC-Raman technique. The results give evidence that the framework titanium species is the active center and Ti–OOH (η2) is the active intermediate. The presence of extra-framework Ti species is harmful to propylene epoxidation. Furthermore, the amorphous Ti species has a more negative effect on the yield of propylene oxide (PO) than the anatase TiO2. The NH3-TPD results reveal that the amorphous Ti species are more acidic and thus should be mainly responsible for the further conversion of PO.

Hierarchical titanosilicate composites (HTS) have been synthesized by an aerosol spray method, by which TS-1 nanoparticles were assembled with cetyl trimethyl ammonium bromide and tetraethylorthosilicate/tetra-n-butyl titanate to form a hierarchical porous composites with a core–shell structure. The structure, porosity, morphology and composition of the materials were characterized by X-ray diffraction, nitrogen adsorption isotherm, Raman spectroscopy, electron microscopy and X-ray fluorescence spectroscopy. The hierarchical porous molecular sieve combines the advantages of TS-1 and Ti-KIT-1, and shows high activity and selectivity to epoxide in cyclohexene epoxidation with H2O2. The yield of cyclohexene oxide on HTS is much higher than those on TS-1 and Ti-KIT-1. The selectivities to cyclohexene oxide and 1,2-cyclohexanediol can be adjusted by varying the titanium contents of the HTS samples.

Here we report a facile and green aerosol-assisted method to synthesize zeolites. Compared with the conventional hydrothermal route, the new method is simpler and less polluting, and requires lower template amount, reaction volume, and crystallization temperature.

•MoOx-modified nanodiamond catalysts were investigated for ODH of propane.•Nanodiamond was found a better carrier than carbon nanotubes for MoOx dispersion.•Low-loading MoOx modified nanodiamond exhibits good catalytic performance.•sp3–sp2 hybridized structure is formed during the reaction.MoOx-modified nanodiamond (ND) catalysts were investigated for oxidative dehydrogenation (ODH) of propane. The catalysts were prepared by impregnation method and characterized by TEM, XRD, XPS, Raman and FTIR spectroscopies. ND was found a better carrier than carbon nanotubes (CNTS) for MoOx dispersion. The MoOx species are two-dimensional polymerized MoOx which get covalently bonded onto the ND surface via MoOC bonds. A major portion of Mo6+ species was found, together with a small amount of Mo4+ species. Adding 1 wt% MoOx on ND (1Mo) can increase both propane conversion and propene selectivity, whereas excess MoOx leads to a drastically decrease in propene selectivity due to the aggregation of the MoOx species and the coverage of the active sites of ND. Both ND and 1MoOx/ND catalysts show good stability after a few hours of testing. A sp3–sp2 hybrid structure is formed in situ and the ketonic/diketonic carbonyl groups are generated during the reaction, which are believed to be favourable to the reaction. Our results indicate the modification of ND by low-loading MoOx can improve the selectivity at the same conversion rate, thus enhance the propene yield.

Iodo-Bodipy immobilized on porous silica was used as an efficient recyclable photocatalyst for photoredox catalytic tandem oxidation–[3+2] cycloaddition reactions of tetrahydroisoquinoline with N-phenylmaleimides to prepare pyrrolo[2,1-a]isoquinoline.

•The products and transformation rate are dependent on the alkalinity.•A 4-membered ring species is an intermediate for recrystallization process.•A cooperative interaction of liquid and solid phases is required.The phase transformation mechanism of zeolite NaY under alkaline hydrothermal conditions was investigated by UV Raman spectroscopy, X-ray diffraction, X-ray fluorescence and scanning electron microscopy techniques. The results revealed that the products and transformation rate are dependent on the alkalinities. All of the starting and resulting zeolites are constructed with the 4-ring and 6-ring secondary building units. The products have lower Si/Al ratio, higher framework density and smaller pore size, which are more stable under alkaline hydrothermal condition. During the phase transformation the fragments of faujasite are formed, then the fragments combine to form different zeolites depending on basicity. Zeolite NaY crystals are consumed as the reservoir for the transformation products during the recrystallization process. For the first time, a 4-membered ring intermediate was found at the early stage of the recrystallization process. A cooperative interaction of liquid and solid phases is required for inducing the phase transformation.Phase transformation of NaY zeolite under alkaline hydrothermal condition is achieved by the cooperative interaction of the liquid and solid phases. A 4-membered ring species is an intermediate for recrystallization process.

A micro-mesoporous molecular sieve ZK-1 was synthesized at 170 °C by a facile one-step hydrothermal method. The structure of ZK-1 can be controlled by the crystallization time. ZK-1(I), the KIT-1 containing ZSM-5 building units in the pore walls, is formed during 2–6 h. ZK-1(II), A mixture of ZSM-5 and KIT-1, is formed after 8 h. The framework structure, porosity, morphology and acidity of the obtained materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Transmission electron microscopy, N2 adsorption, X-ray fluorescence, NH3-temperature programmed desorption and 27Al Magic angle spinning NMR spectroscopy. The samples exhibit good steam stability and better catalytic performances in the isomerization of o-ethyltoluene than KIT-1, suggesting their promising applications in the conversion of large molecules.

The formation process of MCM-41 containing zeolite Y building units has been investigated by UV Raman spectroscopy, 29Si and 27Al MAS NMR spectroscopy, X-ray diffraction (XRD), N2 adsorption and electron microscopy (SEM and TEM). It is found that the precursor containing zeolite Y secondary building units promotes the formation of a metastable mesopore structure just after mixing the zeolite precursors with CTAB. In contrast, the low-polymerized aluminosilicates and well-crystallized zeolite crystals cannot be assembled with CTAB at this stage. The result supports that the zeolite secondary building units should promote to the formation of the mesopore wall. This has been ascribed to its high anionic charge density as well as the appropriate multidentate coordination. Lowering down the pH value to 9.3 facilitates the further polymerization of the aluminosilicate species to build up a stable mesoporous phase.Graphical abstractHighlights► Zeolite Y secondary building units promotes a metastable mesopore formation. ► Low-polymerized silicates cannot induce mesopore formation at high pH. ► Well-crystallized zeolite crystals cannot induce mesopore formation at high pH. ► During the synthesis process the structure and locations of CTAB changes.

The effects of surfactants, counterions and additive salts on the formation of siliceous mesoporous molecular sieves during self-assembly process were investigated by UV Raman spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The surfactant molecules experience the rearrangement after adding the silica species and adjusting the pH value. The obvious change of the Raman bands related to the surfactants supports a cooperative interaction between surfactant and inorganic species during self-assembly process. The addition of EDTANa4 to the system induces the interaction between the COO− groups of EDTA4− and silanol groups of silica and a strong interaction between the EDTA4− and the N+(CH3)3 groups of the surfactant. The above interactions may be the main reason for the salt effect. The new information from the change of the chemical bonds allows for a further analysis to the interactions of different salts between surfactants and silica species at molecular level.Graphical abstractHighlights► The formation of mesoporous molecular sieve was studied by UV Raman spectroscopy. ► A cooperative interaction between surfactant and silica is supported. ► The strong interactions between silica, surfactant and EDTA induce salt effect.

The reaction intermediates for propylene epoxidation were investigated by in situ UV Raman spectroscopy. A feature at 837 cm–1, which has been assigned to the O–O stretching mode in the Ti–OOH (η2) species, was observed in Raman study for the first time. The physisorbed H2O2 and triangular Ti(O2) species are also present at different stages during the in situ measurement. The results obtained by gas chromatography-Raman spectrometry (GC-Raman) during the propylene epoxidation process give direct evidence that the 6-coordinated Ti–OOH (η2) intermediates are important active sites for propylene epoxidation. After adding CH3OH to the TS-1/H2O2/H2O/system, the Raman spectra show the existence of a Ti–O–CH3 moiety and 6-coordinated Ti–OOH (η2) species. The five-numbered ring titanium hydroperoxo intermediate was not detected in this study. The results showed that the 6-coordinated Ti–OOH (η2) species are active sites in the methanol-included epoxidation reaction process.

The effect of zeolite Y precursor on the formation of MCM-41 containing zeolite Y building units has been investigated by means of UV Raman spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (IR) and electron microscopy (SEM and TEM). Study of the precursor formation shows that 4-membered ring species are formed at the early stages of crystallization. Zeolite Y begins to appear after crystallization for 4 h, and its crystallinity increases with increasing crystallization time. However, lowering the pH value to ∼9.3 in the second step not only facilitates the polymerization of silicate species, but also leads to the structural change of the precursors. Pure MCM-41 mesoporous phase containing zeolite Y building units and the mixture of zeolite Y and MCM-41 can be formed combining the effects of the precursor structure and the pH adjustment.

Nanosized mesoporous AlKIT-1 molecular sieve was hydrothermally synthesized in the absence of organic salts. The samples were characterized by X-ray diffraction, electron microscopy (TEM and SEM), N2 adsorption isotherm, and NH3-TPD methods. The AlKIT-1 has a particle size of about 60–100 nm, and a three-dimensional network structure with average pore size of 2.7 nm. The sample exhibits good hydrothermal stability and catalytic performance for 1,2,4-trimethylbenzene, suggesting its promising applications in the conversion of large molecules.

A direct method to controlled synthesis of micro–mesoporous ZSM-5/KIT-1 molecular sieves using dual templates is reported. The framework structure, porosity and morphology of the obtained materials were characterized by X-ray diffraction, infrared spectroscopy, UV-Raman spectroscopy, N2 adsorption isotherm, and electron microscopy (SEM and TEM). It was found that the crystallization temperature is a key to control the framework structure as well as the morphology and hydrothermal stability. Two-phase structure is more favored at higher temperatures, while pure mesophase structure with ZSM-5 building units is formed at lower temperatures. The ZSM-5/KIT-1 crystallized at 130 °C possesses excellent micro–mesoporous structure and good hydrothermal stability. This type of material has a disordered three-dimensional micro–mesopore network structure with narrow pore size distribution and high surface area, which will provide new opportunities for catalytic reactions involving large molecules.

The effects of loading and molar ratio on the structure and reducibility of NiO-MoO3/γ-Al2O3 catalysts have been investigated. Particular attention is given to the catalysts with excess of Mo. The catalysts were prepared by impregnation method and characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and temperature-programmed reduction techniques. Results from Raman, XPS, and XRD show that different surface species can be formed depending on the loading and molar ratio. At low loading spinel-like NiAl2O4 and dispersed MoO3 are the major species on γ-Al2O3. With increasing the loading the aggregation of the Mo species occurs. Only at high loading are crystalline β-NiMoO4 and MoO3 formed on the surface. For the first time, excess Mo was found to promote the formation of β-NiMoO4 on γ-Al2O3. The change in the structure of the catalysts has a large influence on their reducibility, suggesting that both the structure and oxidation−reduction properties of the NiO-MoO3/γ-Al2O3 catalysts can be controlled by varying the loading and molar ratio.

Titanium silicalite (TS-1) zeolites with different titanium species were synthesized and characterized by ultraviolet (UV)-Raman, ultraviolet visible (UV-Vis) diffuse reflectance spectroscopies and by the NH3 temperature programmed desorption (NH3-TPD) method. The roles of different titanium species in TS-1 samples have been investigated by gas chromatography-Raman spectrometry (GC-Raman) during the propylene epoxidation process. For the first time, a positive correlation was found among the concentration of framework Ti species, the amount of active intermediate Ti–OOH (η2) and the conversion of propylene by the in situ GC-Raman technique. The results give evidence that the framework titanium species is the active center and Ti–OOH (η2) is the active intermediate. The presence of extra-framework Ti species is harmful to propylene epoxidation. Furthermore, the amorphous Ti species has a more negative effect on the yield of propylene oxide (PO) than the anatase TiO2. The NH3-TPD results reveal that the amorphous Ti species are more acidic and thus should be mainly responsible for the further conversion of PO.

The effect of zeolite Y precursor on the formation of MCM-41 containing zeolite Y building units has been investigated by means of UV Raman spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (IR) and electron microscopy (SEM and TEM). Study of the precursor formation shows that 4-membered ring species are formed at the early stages of crystallization. Zeolite Y begins to appear after crystallization for 4 h, and its crystallinity increases with increasing crystallization time. However, lowering the pH value to ∼9.3 in the second step not only facilitates the polymerization of silicate species, but also leads to the structural change of the precursors. Pure MCM-41 mesoporous phase containing zeolite Y building units and the mixture of zeolite Y and MCM-41 can be formed combining the effects of the precursor structure and the pH adjustment.

Iodo-Bodipy immobilized on porous silica was used as an efficient recyclable photocatalyst for photoredox catalytic tandem oxidation–[3+2] cycloaddition reactions of tetrahydroisoquinoline with N-phenylmaleimides to prepare pyrrolo[2,1-a]isoquinoline.