Nanocrystalline Aggregates Research Articles

A Nanocrystalline ZSM‐5 for the Catalytic Cracking of Waste Cooking Oil

AbstractA series of hierarchical ZSM‐5 nanocrystalline aggregates (HNZ‐5) was synthesized using a hydrothermal method with tetrapropylammonium hydroxide as a structural guide. The HNZ‐5 samples having different Si/Al molar ratios all showed suitable hierarchical architectures and the maximum surface area was found to be 329 m2/g. The SEM image displayed the width of the individual crystal particles was ~100 nm, and its nanocrystalline clusters generated intercrystalline pores. Temperature‐programmed desorption with NH3 indicated that the total acidity of this material increased with increases in the Al3+ content to a maximum of 0.47 mmol/g at a Si/Al ratio of 15. In addition, 27Al magic angle spinning nuclear magnetic resonance spectra showed that the acid sites were associated with tetrahedral and octahedral Al sites. This HNZ‐5 was applied to the catalytic cracking of waste cooking oil model compound and gave a light olefin yield as high as 43.9 % at 550 °C. Extending the reaction time to 6000 min provided a yield of light olefins in excess of 30 %, which was higher than that achieved using traditional ZSM‐5. These data confirmed that the hierarchical pore structure of HNZ‐5 resulting from the self‐assembly of nanocrystals, together with exposed acidic sites, promoted the catalytic conversion of large molecules.

Unraveling the Structure-Activity-Stability Relationship over Gallium-Promoted HZSM-5 Nanocrystalline Aggregates for Propane Aromatization.

The aromatization of light alkane is an important process for increasing the aromatic production and utilization efficiency of light alkane resources simultaneously. Herein, Ga-modified HZSM-5 catalysts were prepared and investigated by a series of characterization techniques such as X-ray diffraction, nuclear magnetic resonance spectroscopy, transmission electron microscopy, N2 adsorption-desorption, and NH3 temperature-programmed desorption to study their physicochemical properties. The catalytic performance in propane aromatization was also tested. Importantly, the structure-activity relationship, reaction pathway, and coke formation mechanism in propane aromatization were systematically explored. It was found that different Ga introduction methods would affect the amounts of Brønsted and Lewis acid sites, and Ga-HZSM-5 prepared by the hydrothermal method exhibited higher amounts of Brønsted and Lewis acid sites but a lower B/L ratio. As a result, Ga-HZSM-5 showed higher propane conversion and benzene, toluene, and xylene yield compared with that of Ga2O3/HZSM-5. The propane aromatization reaction pathway indicated that propane dehydrogenation to propene was a crucial step for aromatic formation. The increase of the Lewis acid density in Ga-HZSM-5 can effectively improve the dehydrogenation rate and promote the aromatization reaction. Furthermore, the formation of coke species was studied by thermogravimetry-mass spectrometry and Raman approaches, the results of which indicated that the graphitization degree of coke formed over spent Ga-HZSM-5 is lower, resulting in enhanced anticoking stability.

Promoted catalytic performance from furfural to isopropyl levulinate by Zr loaded on defective nanosponge zeolites

Production of alkyl levulinate (AL) from bio-derived furfural (FUR) is environmental-friendly and sustainable. During such process, bifunctional Zr/zeolite catalyst has been demonstrated highly efficient, in which synergism of metal-zeolite and porous structure of catalysts play important roles. In this work, a defective nanoaponge ZSM-5 zeolite loading Zr catalyst is prepared for conversion of FUR to produce isopropyl levulinate (IPL). The defective nanosponge zeolite is hydrothermally synthesized sequenced by acid treatment (NP-A). Then the Zr species were introduced in the as-synthesized NP-A zeolite by impregnation and calcination (Zr/NP-A). The NP zeolite composed of nano-crystalline aggregates deliver hierarchical pores, which promotes adsorption and activation of isopropanol. And the generation of framework Zr accelerates the adsorption of FUR. The as-synthesized Zr/NP-A catalyst give IPL yield up of 77.8 mol% after 3 h reaction at 200 °C with turnover frequency of 8.3 mmol g−1 h−1, which provides an efficient catalyst for production of AL through bio-route.

Uniform Ni species encapsulated in nanocrystalline ZSM–5 with enhanced catalytic performance for upgrading of fatty acids

Acid hydrolysis of silicon source with ethylenediamine complexed Ni as metal precursors was used to synthesis a hierarchical ZSM–5 zeolite supporting Ni catalyst by one-pot method. After sequenced hydrothermal synthesis, calcination and reduction, highly dispersed Ni nanoparticles (NPs) encapsulated in hierarchical ZSM–5 catalyst (Ni@HZ) was obtained. The prepared catalyst was used for upgrading of fatty acids under H2 atmosphere. The Ni@HZ catalyst composed of nanocrystalline aggregates (∼100 nm), induced the generation of abundant intercrystallite mesopores, which promoted the diffusion of the reactants. Moreover, the uniformly distributed Ni NPs internal of nanocrystalline show high thermal stability, thus facilitating the adsorption and spillover of active hydrogen. High conversion rate of palmitic acid and stearic acid with deep deoxygenation were achieved by the synergism of acid and Ni species. Moreover, hierarchical pores in Ni@HZ catalyst improved the selectivity of isomeric products, which benefited the cold flow properties of the upgraded oil.

Synthesis of ultra-small NaA zeolite nanocrystals at near room temperature

The NaA zeolite nanocrystalline aggregates composed of 6 nm ultra-small were synthesized for the first time by refluxing at near room temperature and atmospheric pressure. NaA zeolite samples had been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption isotherms. The XRD of the obtained samples at different synthesis temperatures demonstrated that their crystallinity was high. Furthermore, the SEM images of NaA zeolite synthesized at 30, 40 and 60 °C showed that its particle sizes were 130, 130 and 180 nm, respectively. Moreover, the TEM images confirmed that the NaA zeolite aggregates synthesized at 40 and 60 °C consisted of ultra-small crystals with a size of 6 nm, while the NaA zeolite synthesized at 30 °C was a single crystal. Compared with the previously reported synthetic zeolite crystals, the use of a reflux system under atmospheric pressure in this study not only synthesized the ultra-small zeolite nanocrystals (6 nm) with large specific surface area, but also avoided many safety issues brought by traditional synthesis methods under high autogenous pressure. Therefore, this study provides a precise and safe synthetic method for the development of ultra-small zeolite nanocrystals. Moreover, the large specific surface area makes them have great potential for development.

Seed-induced synthesis of hierarchical architectures of ZSM-5 nanocrystalline aggregates by the solid state crystallization

A seed-induced rapid synthesis of hierarchical ZSM-5 aggregates was achieved by the solid state conversion method in an inorganic system. No secondary mesoporogen was introduced to construct supplementary pore. The physical and chemical properties of the products were characterized by using XRD, SEM, TEM, XRF and N2 adsorption–desorption techniques. The results revealed that the synthesized samples typically exhibit the uniform spherical zeolite ZSM-5 aggregates composed of loosely packed nanocrystals. It was clearly found that the morphology, mesoporosity and particle size of synthesized samples were directly affected by the type of the seed and synthesis conditions. The well-dispersed hierarchical ZSM-5 aggregates were synthesized at NaOH/SiO2 = 0.15, 20 ≤ SiO2/Al2O3 ≤ 40 with the acid of zeolite seed solution in guiding the structure. In addition, the crystal growth of zeolite samples synthesized with zeolite seed solution was studied at 433, 453, and 473 K. The results suggested that the activation energies for the induction, transition and crystallization stages were 91.44, 104.37 and 77.68 kJ∙mol−1, respectively. The method provides a cost-effective and industrially applicable route to synthesize hierarchical ZSM-5 aggregates.

Microcellulose Vs Nanocellulose – A Review

Cellulose is the most abundant and renewable natural semi-crystalline polysaccharide. This biopolymer is an inexhaustible source of natural fibers (NFs), and valuable raw material for the production of microparticles of microcrystalline (MCC) and powdered cellulose (PC), as well as other cellulose micro-products, which are widely used in biomedicine, production of food additives, plastics, and other materials. In addition, cellulose has a nano-fibrillar architecture that promotes the release of free cellulose nanofibers (CNFs) and nanocrystals (CNCs). This review article describes the preparation methods, structural characteristics, properties, and applications of different types of micro- (NFs, MCC, and PC) and nano-cellulose (CNFs, CNCs). Two main shortcomings hindering the wide application of various types of Nano cellulose (NC) were discovered, such as high production expenses and the difficulty of competing with commercial types of micro-cellulose. To reduce the production cost of NC, a waste-free technology can be used, which allows completely utilize materials and chemicals, and produce cheap nanocrystalline aggregates (NCA) with zero emission of liquid and solid waste. Due to the low cost, such a nanostructured product, NCA, will be quite competitive with commercial micro-celluloses (MCC, PC, etc.) and can be used, e.g., as filler and thickener.

Core-Shell Fe2O3@La1-xSrxFeO3-δ Material for Catalytic Oxidations: Coverage of Iron Oxide Core, Oxygen Storage Capacity and Reactivity of Surface Oxygens.

A series of Fe2O3@LSF (La0.8Sr0.2FeO3−δ perovskite) core-shell materials (CSM) was prepared by infiltration of LSF precursors gel containing various complexants and their mixtures to nanocrystalline aggregates of hematite followed by thermal treatment. The content of LSF phase and amount of carboxyl groups in complexant determine the percent coverage of iron oxide core with the LSF shell. The most conformal coating core-shell material was prepared with citric acid as the complexant, contained 60 wt% LSF with 98% core coverage. The morphology of the CSM was studied by HRTEM-EELS combined with SEM-FIB for particles cross-sections. The reactivity of surface oxygen species and their amounts were determined by H2-TPR, TGA-DTG, the oxidation state of surface oxygen ions by XPS. It was found that at complete core coverage with perovskite shell, the distribution of surface oxygen species according to redox reactivity in CSM resemble pure LSF, but its lattice oxygen storage capacity is 2–2.5 times higher. At partial coverage, the distribution of surface oxygen species according to redox reactivity resembles that in iron oxide.

In situ formed robust submicron-sized nanocrystalline aggregates enable highly-reversible potassium ion storage

We report an electrode architecture made of submicron-sized nanocrystalline aggregates obtained in situ from ball-milled BiSb crystals during the potassiation/depotassiation process for use as a potassium ion battery electrode with high electrochemical performance and great stability. Nanocrystalline aggregates are individual particles composed of nanocrystals clustered together. The interconnected nanoparticle network as a potassium ion battery (PIB) electrode shows various advantageous characteristics, including adaption to related structures variation, stable SEI layer formation between the interface of electrode and electrolyte, and high efficiency in conductivity and ion migration/diffusion. As the anode of a PIB, the BiSb nanocrystalline aggregate achieves a high capacity of 514.1 mA h g−1 after 100 cycles at 0.25 A g−1, a high-rate capability of up to 10 A g−1, and an ultra-stable life cycle for 6000 cycles. A series of analyses including consecutive in situ X-ray diffraction measurements, in situ electrochemical impedance spectroscopy, and ex situ electron microscopy, are conducted to demonstrate the relevant reaction mechanism of the nanocrystalline aggregates during the evolution of composition as well as their structure during the cycling process.

First Nanoparticles of a Conductor Based on the Organic Donor Molecule BETS: κ-(BETS)2FeCl4.

Nanoparticles of the molecular superconductor (BETS)2FeCl4 were obtained by the electrochemical oxidation of BETS in the presence of [(C2H5)4N]FeCl4 and an amphiphilic imine (OATM), acting as a growth controlling agent. When the reaction was carried out with a molar ratio OATM/BETS of 10, roughly spherical nanoparticles exhibiting sizes in the 10–40 nm range were observed. X-ray diffraction patterns evidenced the growth of (BETS)2FeCl4 nanoparticles with the κ-type structure. The current-voltage characteristic recorded on an individual nanoparticle aggregate was fitted with a Shockley diode model. A saturation current of 1216 pA and a threshold voltage of 0.62 V were extracted from this model. This latter value was consistent with roughly half of the energy gap of the semiconducting nano-crystalline aggregate.

Real time study of grain enlargement in zirconium under room-temperature compression across the \u03b1 to \u03c9 phase transition

We report a synchrotron Laue diffraction study on the microstructure evolution in zirconium (Zr) as it undergoes a pressure-driven structural phase transformation, using a recently developed real time scanning x-ray microscopy technique. Time resolved characterizations of microstructure under high pressure show that Zr exhibits a grain enlargement across the α-Zr to ω-Zr structural phase transition at room-temperature, with nucleation and growth of ω-Zr crystals observed from initially a nano-crystalline aggregate of α-Zr. The observed grain enlargement is unusual since the enlargement processes typically require substantially high temperature to overcome the activation barriers for forming and moving of grain boundaries. Possible mechanisms for the grain enlargement are discussed.

Voids in walls of mesoporous TiO2 anatase nanotubes by controlled formation and annihilation of protonated titanium vacancies

Amorphous TiO2 nanotubes (TNTs) grown anodically on Ti metal in aqueous electrolytes show a crystallization behaviour strongly dependent on the atmosphere used during annealing at high temperature. In wet oxidizing conditions, the amorphous TNTs walls transform into relatively large and well crystallized anatase-like domains permeated by prismatic voids. On the other hand, crystallization of the amorphous nanotubes under dry reducing conditions induces nanocrystalline aggregates that do not show prismatic voids and exhibit different electronic properties. Supported by density functional theory calculations, it is argued that the formation or absence of voids can be understood in terms of formation and condensation of protonated titanium vacancies. Tunable morphology through defect chemical engineering as such, enables TNTs with increased surface area and catalytic activity, which find potential application in supercapacitors, sensors, photocatalysis, photoelectrochemistry, and dye-sensitized solar cells.

Argon diffusion in hypogene and supergene alunites: Implications to geochronology and thermochronometry on Earth and Mars

Argon release mechanisms and diffusivity were quantified for coarsely crystalline hypogene alunite [KAl 3 (SO 4 ) 2 (OH) 6 ] from Marysvale, Utah, and microcrystalline supergene alunite aggregates from Coober Pedy, South Australia. Prior to diffusivity studies, all alunite samples, sorted in the 500–200, 200–100, 100–50, 50–10, and <10 µm sieve-size ranges, were vacuum encapsulated to quantify 39 Ar recoil losses. Incremental-heating of single capsules inserted into Ta-crucibles and heated by a projector-lamp in a specially designed diffusion cell permits quantifying 39 Ar released at precisely measured temperature steps (±1–3 °C). Incremental-heating 40 Ar/ 39 Ar analyses of the various sieve-size ranges yield reproducible ages that are indistinguishable from single grain (1–2 mm) laser-heating 40 Ar/ 39 Ar dating of the same samples. The results, cast in Arrhenius plots, yield activation energies (E a ) ranging from 248.0 ± 18.5 to 281.7 ± 15.2 kJ/mol and ln(D o /a 2 ) from 26.2 ± 2.0 to 27.8 ± 3.2 ln(s −1 ) for hypogene alunite; supergene alunite yield E a ranging between 233.3 ± 5.4 and 293.8 ± 13.7 kJ/mol and ln(D o /a 2 ) between 27.3 ± 1.0 and 36.8 ± 2.6 ln(s −1 ). These diffusion parameters correspond to closure temperatures of 264 ± 22 °C and 246 ± 19 °C for hypogene and supergene alunite, respectively, assuming a cooling rate 100 °C·Ma −1 . In-situ TEM experiments on aliquots of alunite crystals from the same samples indicate that alunite single crystals undergo transformation to nanocrystalline aggregates at 430–460 °C, showing that alunite releases Ar by volume diffusion below ∼430 °C, retains a significant amount of Ar during phase transformation, and proceeds to release Ar by volume or multipath diffusion from a modified polycrystalline structure at T > 460 °C. Isothermal holding time and AGESME modelling using our calculated diffusion parameters indicate that alunite should preserve Ar quantitatively for long periods (4.0 Ga) at Earth and Mars surface conditions, and both hypogene and supergene alunite should preserve original formation ages, independently of precipitation mechanism.

Realization of red shift of absorption spectra using optical near-field effect

In many applications such as CO2 reduction and water splitting, high-energy photons in the ultraviolet region are required to complete the chemical reactions. However, to realize sustainable development, the photon energies utilized must be lower than the absorption edge of the materials including the metal complex for CO2 reduction, the electrodes for water splitting, because of the huge amount of lower energy than the visible region received from the sun. In the previous works, we had demonstrated that optical near-fields (ONFs) could realize chemical reactions, by utilizing photon energies much lower than the absorption edge because of the spatial non-uniformity of the electric field. In this paper, we demonstrate that an ONF can realize the red shift of the absorption spectra of the metal-complex material for photocatalytic reduction. By attaching the metal complex to ZnO nano-crystalline aggregates with nano-scale protrusions, the absorption spectra by using diffuse reflection of the metal complex can be shifted to a longer wavelength by 10.6 nm. The results of computational studies based on a first-principles computational program including the ONF effect provide proof of the increase in the absorption of the metal complex at lower photon energies. Since the near-field assisted field increase improves the carrier excitation in the metal-complex materials, this effect may be universal and it could applicable to CO2 reduction using the other metal-complex materials, as well as to the other photo excitation process including water splitting.

Photocatalytic activity of hierarchical Ti–Zr–ZSM-5 catalysts from attapulgite by MRS

Hierarchical architectures of titanium (Ti)–zirconium (Zr)–zeolite Socony Mobile–Five (ZSM-5) nanocrystalline aggregates were synthesized in a microwave-assisted rapid system. The micro–mesoporous structure and single-site photocatalytic activity of the nanocrystals were developed by using acidized attapulgite (microwave-treated acidized attapulgite) in the precursor solution. The morphology, crystallinity, surface area and porosity of the samples were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen gas (N2) adsorption–desorption. Results demonstrate that titanium–zirconium–ZSM-5 single-site heterogeneous catalysts persist on the typical framework of mordenite framework inverted structure and present a new spherical aggregate morphology made-up of hexagonal nanocrystals. The synthesis time required is reduced from 12 h to 180 min. The hierarchical nanocrystals have a Brunauer–Emmett–Teller surface area (349·51 m2/g) similar to and a mesopore volume larger than (0·23 cm3/g) those of commercial zeolites. The tetrahedrally coordinated metal oxide (titanium and zirconium) moieties were implanted and isolated in the silica matrices of micro–mesoporous ZSM-5 zeolite, which had a significant photocatalytic activity and reusability for degrading methylene blue dyeing wastewater. As a microreactor, the nanocrystals, with single-site photocatalytic activity, are worthy to be investigated further for potential applications in catalysis for dyeing and wastewater treatment.

Nanosized-bulk V-containing mixed-oxide catalysts: a strategy for the improvement of the catalytic materials properties

A series of nanosized-bulk-supported Mo–V–Nb–Te catalysts was prepared. Using a new synthesis approach, nanocrystalline aggregates of the active phase were deposited on a support.

Order–Disorder Phase Equilibria of Regioregular Poly(3-hexylthiophene-2,5-diyl) Solution

The cloud-point curves for solutions of regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) in o-dichlorobenzene as a function of composition were measured using a thermooptical analysis method. The binary polymer solution shows phase equilibria between a single coiled polymer in solution and polymer in nanocrystalline aggregation, in which the coexistence points at the melting temperature (i.e., solid–liquid equilibria) could be described by the theory of melting point depression combined with the Flory–Huggins model. Through the correlation of theory and experimental data, the heat of fusion per crystalline repeat unit (ΔHu = 47.5 J/g) and the binary interaction parameter (χ = 32.6/T) were estimated. When the solutions were further characterized using UV–vis spectroscopy and X-ray diffraction (XRD), the absorption spectra showed a red-shift (λmax = 464 to 518 nm) with increasing P3HT concentration from 0.01 to 6 wt %, and the XRD data displayed a trace of (100) peaks at 2θ = 5.39° with d-spacing of 1.6 ...

Synthesis of hierarchically structured alumina support with adjustable nanocrystalline aggregation towards efficient hydrodesulfurization

The development of highly active hydrodesulfurization (HDS) catalysts is still of great importance in hydroprocessing of the heavy residue oils in industry. Herein, hierarchically structured alumina hollow microspheres with high specific surface area were successfully prepared via a citric-acid-modulated hydrothermal method. With different dosages of citric acid applied, alumina microspheres were assembled with different specific surface areas, pore volumes and acidity. After the loading of the MoNi active components, a series of HDS catalysts were characterized systematically by various relevant techniques; and their catalytic activity and selectivity towards hydrodesulfurization of dibenzothiophene (DBT) were evaluated and compared. It is revealed that, the catalytic efficiency of the catalyst highly depends on the factors including the specific surface area and the acidity, the sulfidity and the dispersion of the active metal components. On this basis, we have established a facile method for preparation of hierarchically structured alumina supports with desirable physicochemical properties and high HDS catalytic efficiency. This work could also provide theoretical guidance for rational design of highly active HDS catalysts.

High-performance ZnO nanosheets/nanocrystalline aggregates composite photoanode film in dye-sensitized solar cells

Novel ZnO nanosheets (NSs)/nanocrystalline aggregates (NAs) composite films were constructed by depositing a ZnO NAs directly on the surfaces of pre-fabricated ZnO NSs through a dip-coating method. The morphology and performance of dye-sensitized solar cells (DSSCs) were studied. The top layers of ZnO NAs improved the light scattering of composite films. The bottom layers of ZnO NSs consisted of 20–30 nm nanoparticle has a single crystal structure. In addition, ZnO NSs is vertical conductive substrate, so the bottom layers of ZnO NSs layer have a larger specific surface area and good electron transport. Based on the above advantages, the photoelectric conversion efficiency (PCE) of DSSCs assembled by the ZnO NSs/NAs composite films is 7.95%, which is 81.51% higher than that of ZnO NSs and is close to the highest PCE that has ever been reported (8.03%).

Back-transformation of high-pressure minerals in shocked chondrites: Low-pressure mineral evidence for strong shock

Post-shock annealing of meteorites can destroy their shock-induced features, particularly high-pressure minerals, and complicate the estimation of impact pressure–temperature conditions. However, distinguishing post-shock annealing features from thermal metamorphism effects can be practically difficult. Here we report results from Mbale, a highly shocked L chondrite, to investigate the mechanisms, kinetics and identification criteria for post-shock annealing of high-pressure signatures. Olivine fragments within shock-melt veins in Mbale occur as chemically heterogeneous nanocrystalline aggregates that contain trace wadsleyite and ringwoodite. Their strong variation in fayalite content provides evidence of iron partitioning during transformation of olivine to wadsleyite, followed by back-transformation to olivine after decompression. Experimental studies of transformation kinetics show that wadsleyite transforms to olivine in seconds at temperatures above ∼1200K and in hours at temperatures between 900 and 1200K. Thermal models of shock-melt cooling show that shock veins in Mbale cooled to 1200K in 1s. The shock pulse must have been shorter than ∼1s to provide the high temperature conditions for post-shock back-transformation of wadsleyite. Many highly shocked L chondrites, which have abundant high-pressure minerals, must have experienced relatively long shock durations combined with rapid cooling of shock-melt regions to preserve high-pressure phases. The most highly shocked samples, such as impact melt breccias, lack high-pressure phases because of post-shock back-transformations.