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The construction of hierarchical titanosilicate beta zeolites with desirably interconnected meso-/microporosity, controllable morphology and enhanced activity of catalytic oxidation is a pervasive challenge in the zeolite community. We report here in the synthesis of the hierarchical titanosilicate beta zeolite with a three-dimensionally ordered mesoporous-imprinted structure (3DOm-i Ti-beta) through the postsynthetic treatment of the parent 3DOm-i Al-beta by successive dealumination and titanation. The highly interconnected intracrystalline meso-/microporosity derived from the well-retained 3DOm-i structure led to both enhanced diffusion property and better accessibility of active sites to the bulky substrates, which was confirmed by the improved catalytic performances in the epoxidation of cyclic olefins (cyclohexene and cyclooctene) compared with the conventional solely microporous Ti-beta and TS-1. Moreover, the demonstrated that 3DOm-i Ti-beta catalyst exhibited not only a superior stability but also a facile recyclability by simple calcination in the epoxidation reaction. [ABSTRACT FROM AUTHOR]

The identity and rate constants of elementary steps in primary reactions of oxidative coupling of methane (OCM) over Pb 2+ and/or F − substituted hydroxyapatite (HAP, Pb-HAP, HAP-F, and Pb-HAP-F) catalysts have been studied. The rigorous kinetics analysis suggests that HAP and HAP-F initiated the reaction between adsorbed methane and O 2 following Langmuir-Hinshelwood behavior. The Pb-HAP and Pb-HAP-F, however, enabled the reaction between gaseous methane and adsorbed O 2 in the Eley-Rideal mechanism. The F − substitution of OH − weakened both O 2 adsorption and C H bond activation, leading to low methane conversion and slightly higher C 2 H 6 selectivity. The substitution of Ca 2+ by Pb 2+ weakened both methane and oxygen adsorptions, but maintained C H bond activation and raised C 2 H 6 selectivity. The present analysis explored for the first time the effects of cation and/or anion in HAP on OCM reactions in which the analysis has been detailed and quantified in the nature of the mechanism-based kinetic models. [ABSTRACT FROM AUTHOR]

Abstract We reported a strategy to synthesize MFI zeolites with tunable properties by tailoring organic structure-directing agents (OSDAs) under the hydrothermal conditions. The tailored surfactants were obtained by tuning the structure of Gemini-type C ph-10-6-6 and Bola-type BC ph-10-6-6 , including alkyl tail chains, ammonium groups and alkyl middle chains. The textural property, morphology and acidity of resulting MFI zeolites were characterized by a complementary combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N 2 adsorption-desorption isotherms and FTIR spectra of pyridine adsorption. Moreover, the correlation between the OSDAs' composition and the inorganic precursor in the fabrication of zeolite framework was investigated by DFT calculations in this study. The catalytic performance of the resulting MFI samples was investigated by the alkylation of mesitylene with benzyl alcohol. The results revealed that the OSDAs without ammonium groups only leaded to form the micro-structure of zeolites, but the OSDAs with ammonium groups can induce the formation of micro- and meso-structure simultaneously, regardless the OSDAs ended with or without alkyl tail chains. In addition, the resulting MFI zeolites showed an improved catalytic activity in alkylation of mesitylene with benzyl alcohol due to the enhanced pore accessibility, the acidity (Brønsted/Lewis) controlled the activation of benzyl alcohol, and the ratio of external surface area (S ext /S BET) governed the selectivity of alkylation reaction. As a result, tailoring the structure of OSDAs can pick another strategy to synthesize MFI zeolites with tunable zeolite structure and catalytic performance. Graphical abstract The morphology and textural property of MFI zeolites were systematically tailored by tuning the molecular structure of organic templates. Image 1 Highlights • The morphology of MFI zeolites can be tuned by changing the structure of amphiphilic molecules. • The MFI zeolites can be synthesized without utilization of quaternary ammonium surfactant. • The structure-directing ability of amphiphilic molecules was investigated by DFT calculation. • The condensed structure of MFI zeolites was unfavorable for alkylation of mesitylene. [ABSTRACT FROM AUTHOR]

Abstract Catalytic methane decomposition (CMD) has a good potential to develop environmentally friendly hydrogen economy, and the catalyst plays a vital role on its applications. In this work, a novel strategy was proposed to fabricate efficient and effective nickel/carbon catalysts for CMD by introducing some additional nickel and K 2 CO 3 into partial steam gasification of coal char. The gasification process is conducive to in situ synthesize nickel crystallites with high reduction degree (the value of Ni0/(Ni0+Ni2+) up to 76%–81%) on the catalyst surface, and it is competent for co-generation of hydrogen-rich gas and nickel/carbon hybrids with large surface areas (around 86–149 m2/g after washing off the residual potassium salts). The nickel/carbon hybrid as the gasification residue could serve as the catalyst for CMD, showing high and stable methane conversion (up to 80%–87%) at 850 °C. It is observed that co-production of hydrogen and filamentous carbons can be achieved in the 600-min process of CMD, thanks to the positive effect of K 2 CO 3 on formation and activity improvement of the nickel/carbon catalyst. Graphical abstract Image 1 Highlights • Robust nickel/carbon catalysts are prepared by partial gasification of coal char. • The gasification residues are used for catalytic methane decomposition (CMD). • K 2 CO 3 plays a positive role on formation and activity improvement of the catalyst. • High and stable methane conversion (about 80%–87% at 850 °C) can be achieved. • Co-generation of hydrogen and filamentous carbons can be obtained by CMD. [ABSTRACT FROM AUTHOR]

Highlights • Four strategies are proposed for methane pyrolysis on nickel/coal-char hybrids. • K 2 CO 3 is used to promote methane conversion on nickel/coal-char hybrids. • K 2 CO 3 plays a key and positive role on the activity and stability of the catalyst. • Effective and efficient route can be achieved for synthesis of the robust catalyst. Abstract Catalytic methane pyrolysis (CMP) is an environmentally benign and promising strategy for hydrogen production. However, one of the important challenges is to creatively design and prepare catalysts with high and stable catalytic activity. To integrate both advantages of traditional metal and carbon catalysts, four effective strategies were proposed to study K 2 CO 3 -promoted CMP on nickel/coal-char hybrids in this work, including: (1) Impregnation-Thermal treatment-Mechanical mixing method, (2) Precipitation-Thermal treatment method, (3) Precipitation-In situ thermal treatment (PIT) method, and (4) Precipitation-In situ thermal treatment-Hydrogen reduction method. The results suggest that the addition of K 2 CO 3 is the key factor to promote the catalytic activity and stability of the nickel/coal-char hybrids regardless of the preparation methods, leading to high and stable methane conversion (higher than 65% at 850 °C) in the whole 300-min CMP process. Compared to the other three preparation methods, the PIT method is considered to be one simpler and more time-saving process for synthesis of robust catalysts for CMP. [ABSTRACT FROM AUTHOR]

Hierarchical SAPO-34 zeolites with three-dimensionally ordered mesoporous-imprinted structure (3DOm-i SAPO-34) were first confined synthesized within three-dimensionally ordered mesoporous carbons by multiple hydrothermal (MHT) treatments. With perfect structure replication, the obtained 3DOm-i SAPO-34 zeolite particles exhibited unique ordered structures consisting of primary spherical elements of sizes determined by mesopore cages of the corresponding carbon templates, and the sizes of mesopores constituted by the adjacent spherical elements can be precisely tuned from 5.5 to 13.0 nm by varying the 3DOm carbon. The as-synthesized hierarchical 3DOm-i SAPO-34 catalysts showed superior catalytic performance in the MTO reaction with prolonged catalytic lifetime and significant improvement of selectivity for light olefins (ethylene and propylene) compared to the conventional microporous SAPO-34. [ABSTRACT FROM AUTHOR]

The pillared MWW (PMWW or MCM-36) and pillared MFI (PMFI) zeolites are 2-dimensional (2D) catalytically active materials made by pillaring of layered MCM-22(P) and multilamellar MFI precursors, respectively. The single- or near single-unit-cell thick 2D microporous layers in PMWW and PMFI expose comparable number of external surface acid sites ( i.e. , acid sites enclosed in mesopores between zeolitic layers) to those in micropores, which become important or dominant contributor to the catalytic properties. Although the acidity and catalytic activities of PMWW and PMFI have been studied, modification of their external surfaces and its implications on catalytic reactions are not available. In the present study, we report the tailoring of external surfaces of PMWW and PMFI zeolites by atomic layer deposition (ALD) of silicon (ALD-Si) and aluminum (ALD-Al), respectively. The textural, acidic and catalytic properties of the ALD modified pillared zeolites were investigated using a variety of characterization methods. ALD-Al and ALD-Si modifications kept micropore almost intact, but resulted in significant reduction in mesopore volume and considerable changes in external surface composition and acidity. The catalytic tests showed that intrinsic catalytic behavior of Brønsted acid sites in ALD modified pillared zeolites was similar to their parent counterparts. In diffusion constrained parallel reactions, ALD of Al- or Si-species altered catalyst selectivity. In addition, ALD of Si-species on PMFI zeolite deactivated surface active sites, which resulted in improved catalytic activity in direct methane aromatization reactions under optimal ALD cycles. The study exemplified for the first time that ALD is an effective tool for tuning the surface properties of 2D unit-cell thick zeolites. [ABSTRACT FROM AUTHOR]

A one-pot facile route for preparing hierarchically layered titanosilicate-1 (LTS-1) zeolites with stable interlayered mesopores was proposed by integrated using bolaform surfactant (BC ph-12-6-6) and tetrapropyl ammonium hydroxide (TPAOH) as dual templates. By tuning the molar ratios of BC ph-12-6-6 /TPAOH from 5/0 to 5/9, the corresponding LTS-1 samples showed continuous transformations in morphology and intensified degrees of intergrowth by TS-1 nanosheets, resulting in an effective interlayer self-pillaring to avoid the excessive collapse after the removal of the occupied templates by calcination. Moreover, the LTS-1 samples by dual-template synthesis manifested enriched contents of mononuclear octahedrally coordinated Ti species ("TiO 6 "). Benefitted by the highly patulous structure and more accessible Ti active sites predominated with high-performance "TiO 6 " species, the LTS-1 catalysts by dual-template synthesis exhibited a superior catalytic activity in the epoxidation of cyclooctene compared with the layered TS-1 directed by sole template of BC ph-12-6-6 and the conventional bulk TS-1. It is reasonable to expect that the demonstrated work has important implications for the design and facile synthesis of layered titanosilicate zeolite catalysts with a stably hierarchical structure and tunable catalytic oxidation activities by an optimized distribution of titanium coordination states containing the coordinated "TiO 4 " and "TiO 6 " species. [Display omitted] • One-pot dual-template synthesis of hierarchically layered titanosilicate-1 (LTS-1). • Effective interlayer self-pillaring by integrated templating of BC ph-12-6-6 and TPAOH. • LTS-1 manifests enriched contents of mononuclear octahedrally coordinated Ti species ("TiO 6 "). • Improved catalytic epoxidation performances by the highly patulous structure and more accessible Ti active sites. [ABSTRACT FROM AUTHOR]

A novel hierarchical tungsten-substituted Silicalite-1 zeolite with the highly interconnected hollow structure (HWS-1) was synthesized for the first time by post-treating the purely microporous tungsten-substituted Silicalite-1 (WS-1) through simultaneous desilication and tungstation, in which a combination of sodium hydroxide and tetrapropyl ammonium hydroxide (TPAOH) was used to achieve a systematic balance between dissolution and recrystallization and further promote the synchronous tungstation with using sodium tungstate dihydrate as a tungsten source. Under an optimum addition ratio of NaOH/TPAOH, the resulted HWS-1 exhibited not only well retained microporosity and crystallinity but also obviously enlarged external surface area and mesopore volume in contrast to the parent WS-1. Furthermore, the effective tungstation also facilitated the substitution and increased the amount of coordinated W species in zeolite frameworks. The catalytic performance of HWS-1 was evaluated by the epoxidation of cyclohexene with using H 2 O 2 as oxidant. Benefited by the highly interconnected hollow structure and more accessible active sites on the enlarged external surface, the HWS-1 catalyst revealed a higher catalytic activity with improved cyclohexene conversion than WS-1. Moreover, it was found that a significant positive effect on promoting epoxidation was achieved by tungsten-substituted Silicalite-1 (WS-1 and HWS-1) catalysts reflecting at a much higher selectivity of epoxide (>79%) in comparison with titanium-substituted Silicalite-1 (TS-1) (~50% selectivity of epoxide), due to their superior hydrophobicity and suitably weaker acidity, which further demonstrated the potential application of the developed hierarchical tungsten-substituted Silicalite-1 as a candidate catalyst for epoxidation and other selective oxidation reactions. [Display omitted] • Hierarchical fabrication of tungsten-substituted Silicalite-1 (HWS-1) by postsynthetic treatment. • A systematic balance between dissolution and recrystallization by combined using of NaOH and TPAOH. • The highly interconnected hollow structure provided more accessible active sites. • HWS-1 exhibited enhanced catalytic activity in cyclohexene epoxidation. [ABSTRACT FROM AUTHOR]

Hierarchical two-dimensional (2D) lamellar zeolites represent a young emerging field and a novel expression of the zeolite frameworks. Accompanied with synthesis and catalytic performance investigation, assessment on the local environment and catalytic behavior of acid sites in 2D zeolites are needed. Here, we described the local environment of Lewis acid sites and evaluated catalytic activities of external acid sites (i.e. sites on external surface and in mesopores) in 2D lamellar titanium silicalite-1 (TS-1) zeolites. For comparison purpose, four TS-1 zeolites, including 3D TS-1, multilamellar 2D TS-1 without pillarization and with pillarization by silica and silica/titania, respectively, were prepared. The local environment of Ti-sites, including coordination status of Ti-atom, speciation of hydroxyl (-OH) group that hints degree of confinement, acid site strength and accessibility, was collectively assessed by spectroscopic and organic base titration measurements. Kinetic studies of cyclooctene (C 8 H 14) epoxidation with hydrogen peroxide (H 2 O 2) discerned catalytic activity of external Ti-sites that decreased with increasing mesoporosity due to decrease in site confinement. Image 1 • External Lewis acid sites in 2D TS-1 zeolites were quantified. • 2D TS-1 zeolites have high density of isolated surface silanol and titanol groups. • Reactivity of external sites decreases with increasing mesoporosity in 2D TS-1. • Decrease in reactivity of external sites is caused by loss of partial confinement. • Kinetic decoupling of epoxidation pathways enabled catalytic behavior assessment. [ABSTRACT FROM AUTHOR]