Teng Xue

Direct synthesis of self-assembled ZSM-5 microsphere with controllable mesoporosity and its enhanced LDPE cracking properties

Self-assembled mesoporous ZSM-5 microspheres (∼5 μm), which are composed of inter-growthed primary nano-strips, are directly synthesized using n-hexylamine as the single template. The mesopore distribution can be facilely controlled by adjusting the size of primary particles via modulating the alkalinity of the synthesis gel. The samples obtained by varying Na2O/SiO2 molar ratios from 0.07 to 0.15 are denoted as ZM-X (X = 1–5). The ZM-X samples are characterized by techniques including XRD, TEM, SEM, N2 adsorption–desorption and FTIR. It is found that ZM-3 exhibits a uniform mesopore distribution around 10 nm and possesses the largest amount of external acid sites, which lead to the remarkably enhanced catalytic performance in polyolefin cracking. A possible growth mechanism of self-assembled ZSM-5 microspheres directed by n-hexylamine is proposed.

Synthesis of hierarchical ferrierite using piperidine and tetramethylammonium hydroxide as cooperative structure-directing agents

Zeolite ferrierite aggregates with hierarchical porosity were synthesized using TMAOH and piperidine as cooperative structure-directing agents (co-SDAs). The effect of the relative amount of TMAOH and piperidine on the crystalline phase and textural properties of the products was investigated. Ferrierite aggregates synthesized herein were ca. 10–15 μm in size, comprised of nanosheets with thickness of less than 50 nm. The ferrierite aggregates possessed similar acidity and crystallinity with respect to the bulk ferrierite prepared using only piperidine as SDA, but exhibited more than 3 times higher mesopore surface area. The ferrierite aggregates with hierarchical porosity were found to be more efficient in catalytic LDPE cracking due to improved accessibility of large polymer molecules to the active sites.

One-step post-synthesis treatment for preparing hydrothermally stable hierarchically porous ZSM-5

Abstract Hierarchically porous ZSM-5 (SiO2/Al2O3 ≈ 120) containing phosphorus was prepared by a one-step post-synthesis treatment involving controlled desilication and phosphorous modification. The hierarchically porous ZSM-5 featured high thermal and hydrothermal stability. The obtained ZSM-5 zeolites were systematically characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, NH3 temperature-programmed desorption, and 27Al and 31P magic-angle spinning nuclear magnetic resonance spectroscopy. The prepared ZSM-5 displayed enhanced activity and prolonged lifetime toward hydrocarbon cracking. The high activity was attributed to improved coke tolerance owing to the presence of the highly stable mesoporous network of ZSM-5 and acid sites introduced upon phosphorus modification. Additionally a mechanism of the stabilization of the zeolites by phosphorus was proposed and discussed.

Low temperature hydrogenation of α-angelica lactone on silica supported Pd–NiO catalysts with synergistic effect

The hydrogenation of α-angelica lactone (α-AL) was achieved under mild conditions on silica supported Pd–NiO catalysts. NiO and palladium were sequentially loaded on silica by wet-impregnation and deposition–reduction, respectively. First a series of NiO/SiO2 supports with varying Ni contents were prepared by a wet-impregnation method with Ni(NO3)2 as the precursor followed by calcination in air. Then a minute amount of palladium (0.2 wt%) was loaded by a deposition–reduction method using NaBH4 as a reducing reagent. The Pd–NiO catalysts were characterized by nitrogen adsorption, XRD, H2-TPR, XPS and TEM. The NiO were heterogeneously dispersed on silica with particle sizes ranging from 10 to 50 nm, whereas Pd was finely loaded with a diameter less than 5 nm. Nanoscale intimacy between Pd and NiO was noticed by HRTEM, resulting in high catalytic activity in liquid phase hydrogenation of α-angelica lactone to γ-valero lactone (GVL) under mild conditions. 0.2Pd–9.9NiO/SiO2 showed the best activity among all the catalysts investigated, with 82% conversion and 100% selectivity to GVL within several minutes at 30 °C and 0.3–1 MPa H2 pressure.

Enhanced CO2 adsorption on Al-MIL-53 by introducing hydroxyl groups into the framework

A series of hydroxyl functionalized Al-MIL-53 materials (Al-MIL-53-OHx) containing varying hydroxyl molar ratios (x = 25%, 50%, 75%, and 100%) were synthesized via a mixed-linker approach, wherein x denotes the molar ratio of 2,5-dihydroxy terephthalic acid:(2,5-dihydroxy terephthalic acid + terephthalic acid). All Al-MIL-53-OHs exhibited an identical structure to that of Al-MIL-53. The thermal stability of Al-MIL-53 decreased after introducing hydroxyl groups. The hydroxyl functionalized Al-MIL-53 containing 25 mol% and 50 mol% of hydroxyl group showed higher surface areas (SBET = 1270 and 1260 m2 g−1 for Al-MIL-53-OH25 and Al-MIL-53-OH50, respectively) than that of Al-MIL-53 (SBET = 819 m2 g−1). A further increase in the OH groups (75 mol% and 100 mol%) led to dramatical compromise of the framework. The presence of hydroxyl groups affected not only the CO2 adsorption capability but also the ‘breathing effect’ of MIL-53 resulting from the intraframework interaction. The CO2 adsorption capacities of Al-MIL-53-OH25 and Al-MIL-53-OH50 at 1 bar at 25 °C were 8.5 and 8.3 wt%, respectively, which are about 19% higher than that of Al-MIL-53 under the identical conditions. Moreover, pronounced improvement in CO2 adsorption was observed below 0.2 bar, especially for Al-MIL-53-OH25 (5.5 wt% for Al-MIL-53-OH25 vs. 1.7 wt% for Al-MIL-53). This behavior is due likely to the enhanced isosteric heat of CO2 adsorption. The hydroxyl group plays a positive role in the CO2 adsorption performance of Al-MIL-53, which is comparable to amino groups. Al-MIL-53-OHx (x = 75 and 100) displayed lower CO2 adsorption capacities despite the higher isosteric heat of CO2 adsorption, which might be due to the blocked pores in the presence of dense hydroxyl groups.

Seed-induced synthesis of small-crystal TS-1 using ammonia as alkali source

Abstract Small-crystal TS-1 was synthesized via a seed-induced approach using ammonia as the alkali source and tetrapropylammonium bromide as an auxiliary structure-directing agent. The TS-1 samples were characterized using X-ray diffraction, N2 adsorption-desorption, Fourier-transform infrared spectroscopy, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, and ultraviolet-visible spectroscopy. The use of the colloidal seed reduced the crystal size, and an appropriate amount of silicalite-1 seed assisted Ti incorporation into the TS-1 framework. This method reduces the cost of TS-1 synthesis because a significantly smaller amount of tetrapropylammonium hydroxide is used. The catalytic performance of the synthesized small-crystal TS-1 samples in cyclohexanone ammoximation was better than that of bulk TS-1 as a result of improved diffusion and a larger number of active tetrahedral Ti centers.

Hierarchical ZSM-5 nanocrystal aggregates: seed-induced green synthesis and its application in alkylation of phenol with tert-butanol

Hierarchical ZSM-5 zeolite aggregates were synthesized in an organic-template-free system via seed-induced crystallization. The obtained samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption, NH3 temperature-programmed desorption (NH3-TPD) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The prepared ZSM-5 nanocrystalline aggregates possessed open/accessible hierarchical pores and active sites, showing significant advantages in the catalytic alkylation of phenol with tert-butanol. The obtained materials could maintain the activities of the nanocrystal zeolites and meanwhile could be easily separated or recovered during the preparation and reactions. This approach was simple and also overcame the commonly-seen drawbacks such as the exceeded use of specific templates or secondary templates during the synthesis of the hierarchical zeolites.

Core–Shell Zeolite Y@γ‐Al2O3 Nanorod Composites: Optimized Fluid Catalytic Cracking Catalyst Assembly for Processing Heavy Oil

Compositions, structures, and distributions of the active phases in fluid catalytic cracking (FCC) catalysts have an essentially important impact on their porosities, acidities, and thus cracking capabilities for processing heavy oil fractions. Here, we report a facile approach for fabrication of core–shell zeolite Y@γ‐Al2O3 nanorod composites by controlling the attachment of boehmite nanorods on the external surface of zeolite crystals, and thus regulating the dispersion and combination of the active alumina matrix on zeolite components in the FCC catalyst. The synthesized discrete boehmite nanorods possess a large quantity of positive charges and can directly electrostatically interact with the negative surface of zeolite crystals, leading to the formation of core–shell zeolite Y@γ‐Al2O3 nanorod composites (nY@Al2O3). The optimized 4Y@Al2O3 composite (Y/γ‐Al2O3 weight ratio of 4) with zeolite crystals fully embedded by alumina nanorods shows enhanced textural properties, acidity accessibilities, and improved cracking ability of 1,3,5‐triisopropyl benzene. Taking it as the main active component, the produced FCC catalyst shows better contaminant resistant ability and especially higher gasoline yield in the cracking of heavy oil, which could potentially bring practical economic profits for the oil‐refining industry.