Search

In this work we explore the deposition of gold onto a silicoaluminophosphate, using a variety of known nanoparticle deposition techniques. By comparing the gold particles deposited on a traditional microporous aluminophosphate, with an analogous hierarchical species, containing both micropores and mesopores, we explore the influence of this dual porosity on nanoparticle deposition. We show that the presence of mesopores has limited influence on the nanoparticle properties, but allows the system to maintain porosity after nanoparticle deposition. This will aid diffusion of reagents through the system, allowing continued access to the active sites in hierarchical systems, which offers significant potential in catalytic oxidation/reduction reactions.

Oligomerization of light olefin is an effective method to produce plentiful liquid fuels. However, oligomerization processes using microporous zeolites have severe problems due to steric hindrance. In this paper, oligomerization of butene using a series of new types of hierarchical HZSM-5 zeolite catalysts is studied. To obtain the modified HZSM-5 catalysts, HZSM-5 is treated with the same concentration of LiOH, NaOH, KOH, and CsOH aqueous solutions, respectively. It is demonstrated that the alkali treatment can effectively modify the acidity properties and hierarchical structure of the HZSM-5 catalyst, which is confirmed by X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Nitrogen Adsorption-desorption Measurements, Transmission Electron Microscopy Investigations (TEM), Ammonia Temperature-programmed Desorption Method (NH3-TPD), Pyridine FT-IR, and Thermogravimetric Analysis (TGA). The results show that hierarchical catalysts with interconnected open-mesopores, smaller crystal size, and suitable acidity can better prolong the catalyst lifetime during butene oligomerization. Particularly, the HZSM-5 catalysts treated with CsOH aqueous solution (ATHZ5-Cs) proved to be the most effective catalyst, resulting in approximately 99% conversion of butene and exhibiting C8+ selectivity of 85% within 12 h. Thus, an appropriate hierarchical catalyst can satisfy the oligomerization process and has the potential to be used as a substitute for the commercial ZSM-5 catalyst. [ABSTRACT FROM AUTHOR]

Cost-effective and efficient catalysts for pyrolysis and catalytic cracking can be derived from low-cost and abundantly available natural minerals. Herein, we report the fabrication of hierarchical mordenite (MOR) zeolites with an enhancement in micropore properties, which were obtained by ion exchange followed by dealumination of natural zeolites. Crystallinity, textural properties and morphologies of the hierarchical catalysts were characterized by using X-ray diffraction (XRD), nitrogen physisorption and field-emission scanning electron microscopy (SEM). The XRD patterns show that the parent minerals contain natural mordenite as the dominant phase (73–83 wt%). The severity of the dealumination was studied by applying different concentrations of nitric acid (HNO 3 ). Dealumination affected crystallinity, Si/Al ratio, mesoporosity of mordenite, and selectivity of products in n-hexane cracking. Crystallinity of hierarchical MOR decreased with higher HNO 3 concentrations. High selectivity to propylene with propylene/ethylene ratio of 1.26 was achieved over mordenite treated with mild dealumination by HNO 3 (1 M). These cost-effective catalysts derived from natural zeolites are potentially applied in chemical industries. [ABSTRACT FROM AUTHOR]

Fe nanoparticles (∼10 nm), used to grow carbon nanotubes (CNTs), have an outstanding ability to catalyze the dehydrogenation of LiAlH4. The CNTs help connect Fe and LiAlH4 and create microchannels among the composite, thus promoting the release of hydrogen. Inspired by these results, a supercritical-CO2-fluid-assisted deposition technique is employed to decorate the Fe/CNTs with highly dispersed nanosized Ni (∼2 nm in diameter) for better performance. With the incorporation of 10 wt % of this hierarchical catalyst (Ni/Fe/CNTs), the initial dehydrogenation temperature of LiAlH4 is decreased from ∼135 to ∼40 °C. At 100 °C, this catalyzed LiAlH4 takes only ∼0.1 h to release 4.5 wt % hydrogen, which is more than 100 times faster than the time needed with pristine LiAlH4. The dehydrogenation mechanism of the complex hydride is examined using in situ synchrotron X-ray diffraction. [ABSTRACT FROM AUTHOR]

Abstract: A series of modified TS-1 samples have been produced by desilication of the original TS-1 (4wt.% Ti) using a chemical treatment with NaOH. Desilicated TS-1 zeolites exhibit a large BET surface area together with a well-developed mesoporosity. The hierarchical catalysts from desilication of TS-1 zeolite show a good catalytic activity for the oxidation of small molecules and a significantly higher activity for the oxidation of bulky molecules. [Copyright &y& Elsevier]

• Ru 0.05 Ce 0.95 O 2-y (∼3 nm) catalyst stabilized on silane-modified Al 2 O 3 was prepared. • The catalyst was highly stable in reducing and oxidizing atmosphere. • Ex-solution/redispersion reversibility of Ru ions in CeO 2 was proved. • Propane oxidation activity was improved after activation of catalyst in H 2. • The catalyst can be reactivated after the catalytic processes by heating in H 2. In this work, we synthesized and characterized a novel catalyst containing Ru 0.05 Ce 0.95 O 2-y nanoparticles (2–5 nm) deposited on the functionalized γ-Al 2 O 3 support. The catalyst was studied with a wide range of ex-situ (STEM-HAADF/EDS, TEM, BET, Raman spectroscopy, XRD) and in situ methods (TPR-TPO, XPS with in situ thermal treatments) in order to determine its behavior during the successive reduction-oxidation treatments. The system shows good reversibility of the noble metal ex-solution on the particles' surface and its redispersion in the cerium oxide structure, with excellent stability of nanoparticles' morphology. The catalyst was active in the propane oxidation at 210℃ and could be reactivated by heating in hydrogen at 500℃. [ABSTRACT FROM AUTHOR]

• Cracking of C 12 -C 32 hydrocarbon by hierarchical catalyst was tested using CPP method. • The conversions were improved with increasing the number of carbon in raw materials. • Hierarchical catalysts showed higher reactivity than zeolite-kaolin mixed catalysts. • Gasoline yield increased linearly with increasing the conversion for all catalysts. • Y-zeolite-containing catalysts exhibited the higher ratios of branched hydrocarbons. Catalytic cracking of C 12 -C 32 hydrocarbons as model compounds was performed using hierarchical zeolite-containing mesoporous silica and silica-alumina. Curie point pyrolyzer (CPP) was used as a new evaluation method of catalytic cracking. The activity and product selectivity using hierarchical catalysts were compared with those of zeolite-kaolin mixed catalyst. The conversion and gasoline yield were improved with increasing the number of carbon in raw materials, and alkene showed higher reactivity than alkane compared with the same carbon number. It was thought that the hierarchical catalysts, which had the larger amounts of mesopores, would show the higher gasoline yield and conversion than kaolin mixed catalysts. Regardless of the type of zeolite, the gasoline yield increased linearly with increasing the conversion. In contrast to this, Y-zeolite-containing catalysts exhibited the higher ratios of branched hydrocarbons probably because of the presence of its larger micropores. [ABSTRACT FROM AUTHOR]

The objective of this review is to describe recent advances in preparation and reactivity of hierarchical catalysts for catalytic cracking of carbonaceous materials consisting of not only simple straight-chained and substituted aromatic hydrocarbons but also heavy molecules such as vacuum gas oil, atmospheric residue and biomass like vegetable oil. Catalysts for catalytic cracking are mainly composed of matrix and zeolite. It has been well-known that, since the content of zeolite is usually smaller than that of matrix, zeolite is approximately surrounded by matrix particles. This means that the catalysts of catalytic cracking forms a hierarchical structure even if major component of matrix would be kaolin which has not significant pores. Zeolite has micropores and very high activity for cracking while kaolin does not have the activity for cracking but the catalysts have the very large size and wide range of pores from micropores to mesopores and macropores which promote the diffusion of not only reactants but also products. Preparation, characterization and reactivity of zeolite with the high catalytic activity have extensively been reported, however it has not necessarily been clarified for a long time how the amounts and the sizes of pores in matrix affect the reactivity in catalytic cracking. Recent advances in preparation methods of not only zeolite but also mesoporous materials are remarkable and the advantages of hierarchical structure in catalysts for catalytic cracking have extensively been reported. These include novel mesoporous zeolites, the combination of zeolite and advanced mesoporous materials, and zeolite surrounded by mesoporous materials, which increased the activity and the selectivity for products in catalytic cracking. The review describes how the hierarchical catalysts are made, how the hierarchical structure act for the reaction and what are the roles of matrix and zeolite in detail. • Recent advances in preparation and reactivity of hierarchical catalysts for catalytic cracking • Novel mesoporous zeolites, advanced mesoporous materials, and their combination • Preparation methods, pore structures and enhancement in activity of hierarchical catalysts • How does the hierarchical structure act for the reaction and what are the roles of matrix and zeolite? [ABSTRACT FROM AUTHOR]

In this work we explore the deposition of gold onto a silicoaluminophosphate, using a variety of known nanoparticle deposition techniques. By comparing the gold particles deposited on a traditional microporous aluminophosphate, with an analogous hierarchical species, containing both micropores and mesopores, we explore the influence of this dual porosity on nanoparticle deposition. We show that the presence of mesopores has limited influence on the nanoparticle properties, but allows the system to maintain porosity after nanoparticle deposition. This will aid diffusion of reagents through the system, allowing continued access to the active sites in hierarchical systems, which offers significant potential in catalytic oxidation/reduction reactions., (Copyright © 2019, Potter et al.; licensee Beilstein-Institut.)