SYNTHESIS OF MESOPOROUS TiOz MATERIALS WITH HIGH SPECIFIC AREA USING INORGANIC ACIDS AS CATALYSTS

This paper presents a synthesis process for preparing mesoporous titanium dioxide materials in the absence of any templates and using inorganic acids as catalysts. Tetrabutyl titanate was used as the precursor at ambient temperature, and four different inorganic acids, i.e., hydrochloric, nitric, sulfuric and phosphoric, were used as catalysts.The as-prepared mesoporous TiO2 materials were characterized by SEM, XRD and nitrogen adsorption/desorption measurements, The influences of different inorganic acids on the properties of TiO2 were discussed and compared in details. Experiments showed that the inorganic acids have significant effects on the surface area, pore volume, pore size,and pore size distribution of the products. The mesoporous TiO2 materials catalyzed by phosphoric acid exhibited the largest specific surface area and largest pore volume with narrow pore size distribution. Vacuum and infrared drying methods tested in the process were found to have subtle impact on the structure of the TiO2 materials prepared,     

SYNTHESIS AND COATING OF ORDERED MESOPOROUS SILICA

1,3,5-trimethyl benzene (TMB) was used as organic swelling agent in O/W emulsions to template ultra-large mesoporous materials using the hydrothermal method. The silicas with well-defined mesopores and hydrothermally robust framework were characterized by X-ray diffraction, transmission electron microscopy and BET surface area analysis. The influence of the quantity of TMB during preparation was studied. It has been found that the TMB/CTAB ratio must be controlled for producing high pore volume materials. Polysulfone (PSU), as the usual extraction agent, was coated on the silicas with the solvent evaporation method to produce a solid separation medium. The adsorptivity and the surface area of the coated MCM were determined: 10% PSU coated MCM adsorbed twice as much phenol as the uncoated material, reaching 0.5 mg/g silica. It was found that the surface area of the coated material decreased rapidly with an increase of the PSU Ioadina.     

NUMERICAL SIMULATION OF THE GROWTH OF NANOPARTICLES IN A FLAME CVD PROCESS

The growth of titania nanoparticles in a flame CVD process has been simulated by computational fluid dynamics, based on the change rate of particle number density due to their collisions calculated from an integral collision kernel. The assumptions made on constant particle volume density nv (nd^3), constant density of particle surface area ns (nd^2), and constant entity nd^2.5 in coagulation process have been examined. Comparisons have been made on particle size distribution between measurement results and predictions from present model of particle growth and Kruis model of particle dynamics for titania nanoparticles synthesized by the flame CVD process. Effects of operational parameters such as O2 mole fraction and particle number density on mean particle size and size distribution have been discussed.     

Progress in the synthesis and applications of hierarchical flower-like Ti02 nanostructures

Flower-like TiO2 materials, with their advantages of high specific surface area, developed pore structure, and high photocatalytic activity, have been widely used in environmental management and air purification, sterilization, and surface self-cleaning, among other areas. This paper summarizes several methods used to fabricate the flower-like TiO2 nanostructures, such as the hydrothermal, solvothermal, microemulsion, sol-gel, hydrolysis, and electrodeposition oxidation methods. In addition, the morphologies, properties, and performance of different flower-like TiO2 structures are discussed. Meanwhile, the application progresses of different flower-like TiO2 structures are also analyzed.     

Effects of internals and distributors on the distribution and growth of bubbles in the conventional gas-solid fluidized bed

The effects of internals and gas distributors on the local dynamics of the bubbles in the conventional gas-solid fluidized bed were studied.Mesh-type internals with different opening areas(50%,70%and 90%)and different arrangements(two-layer and four-layer);and a sintered plate with a smaller pore size(1μm)and a perforated plate with a larger pore size as distributors were investigated.Differential pressure drops and local solids holdups were measured under various superficial gas velocities to compare the performances of the different types of internals and distributors.The instantaneous solids holdup signals from the optical fibre probe were used to further examine the local bubble dynamics in detail.Smaller bubbles were found,with the installation of internals or using the sintered plate,resulting in lower pressure drops and a higher bed expansion.Internals with reduced opening area or distributor with smaller pore size further leads to a higher changeover rate between the bubbles and dense phase,both axially and radially,and hence a better gas-solid contacting and an earlier transition to the turbulent flow regime of the bed.     

TAILORING OF PORE SIZE IN MESOPOROUS SILICA WITH STEARIC ACID AND PVP

Mesoporous silica was prepared using tetrathoxysilane （TEOS）, cetadecyltrimethylammonium bromide （CTAB）, aqueous ammonia, acetone and water as silica source, template agent, precipitator and solvent respectively. Stearic acid and polyvinylpyrrolidone （PVP） were employed as additional templates to tailor the pore size in the resultant porous silica. BET, SAXRD and SEM analyses were used to characterize the surface area, pore size, pore structure, pore regularity and morphology of the sample. BET measurement results showed that PVP could increase the surface area but diminish the pore size while stearic acid could decrease the surface area but enlarge the pore size. SAXRD analysis indicated that more additional template introduction gave rise to less order-structured products. All these various results could be attributed to the differently modified CTAB micelles involving stearic acid and PVP addition.     

In situ synthesis of magnetic mesoporous silica via sol-gel process coupled with precipitation and oxidation

A novel method was proposed for the in situ synthesis of magnetite-containing mesoporous silica SBA- 16 via a sol-gel process coupled with precipitation and oxidation. The effect of the added amounts of reactants on the mesostructural and magnetic properties of the magnetic mesoporous silica was investigated. It was determined that the synthesized magnetic mesoporous silica with a total pore volume of 0.64-0.96 cm 3 /g and an average pore diameter of 4.0-14.9 nm had a relatively high saturation magnetizatio...     

PREPARATION AND MICROSTRUCTURE CHARACTERIZATION OF Ni／TiO2 NANOCOMPOSITE

Homogeneous Ni^2 -doped titania gel was synthesized by a sol-gel process,and the xerogel was then obtained through aging and drying,leading to the formation of Ni/TiO2 nanocomposite after heat treatment under a suitable reducing atmosphere.The resulting nanocomposite was characterized by TGA-DSC,TEM,XRD and BET methods.The results show that the structure and grain size of the nanocomposites could be manipulated by altering the heat-treatment conditions,and that the nanocomposite possesses a mesoporous structure with a pore radius of ca.28nm and a specific surface area of 49.1 m^2.g^-1.It is demonstrated that the nanosized Ni dispersion in the titania matrix significantly affects the anatase-rutile phase transformation.     

Dry modification of electrode materials by roller vibration milling at room temperature

For the first time dry roller vibration milling at room temperature was used to prepare active carbon （AC） nano-particles and to modify MnO2 powder as electrode materials. In 30 min AC was milled to a mean particle size of 30-50 nm with increased crystallinity and higher specific surface area, predominantly mesoporous and with improved pore diameter distribution. Then, AC nano-particles were incorporated with MnO2 or bismuth-doped MnO2 nano-particles synthesized by sol-gel methods to prepare nano-composite electrode materials for studying their electrochemical performance. The AC nano-particles combined with 10 wt.% bismuth-doped MnO2 nano-particles were found to possess excellent electrochemical property with specific capacitance up to 308 F/g and without obvious attenuation with increasing current. Our method seems to ooen a new way to imorove AC based electrode materials used for clean energy such as suner capacitors.     

Preparation of porous silica spheres with self-dispersing properties

A sol-gel procedure in a water/oil emulsion was introduced for the synthesis of porous silica spheres. Tetraethoxysilane was used as the silica source. The specific surface area and total pore volume of the product reached 772.3 m2/g and 0.663 cm3/g, respectively. The electrolyte washing process conferred a surface charge to the product, which displayed self-dispersal properties in water. The porous spheres have potential applications in the fields of drug delivery, controlled release capsules, indoor air pollutant scavengers, and hydrogen storage agents. The oil phase, which accounts for over 8O% of the chemical cost of the procedure, could largely be recycled by filtering, standing, and layering. The whole procedure is suitable for application as an industrial process.     

Dry modification of electrode materials by roller vibration milling at room temperature

For the first time dry roller vibration milling at room temperature was used to prepare active carbon (AC) nano-particles and to modify MnO2 powder as electrode materials.In 30min AC was milled to a mean particle size of 30-50nm with increased crystallinity and higher specific surface area,predominantly mesoporous and with improved pore diameter distribution.Then,AC nano-particles were incorporated with MnO2 or bismuth-doped MnO2 nano-particles synthesized by sol-gel methods to prepare nano-composite electrode materials for studying their electrochemical performance.The AC nano-particles combined with 10 wt.% bismuth-doped MnO2 nano-particles were found to possess excellent electrochemical property with specific capacitance up to 308 F/g and without obvious attenuation with increasing current.Our method seems to open a new way to improve AC based electrode materials used for clean energy such as super capacitors.     

N-doped carbon nanotube encapsulated nZVI as a high-performance bifunctional catalyst for oxidative desulfurization

Great efforts have been made to remove sulfur from fossil fuels to protect the environment. We proposed synthesis of high efficiency oxidation desulfurization (ODS) catalysts by encapsulating nano zero valent iron (nZVI) in self-catalyzed carbon nanotubes. The synthetic strategy features facile hydrothermal and pyrolysis process. The specific surface area, pore structure, and microstructure of the catalysts were characterized by series techniques, and the catalytic ability was evaluated by the reduction of sulfur after oxidation and reflux-extraction. The optimized nZVI@CNT catalyst exhibits outstanding catalytic performance (within 120 min, the oxidative removal rate of DBT reached 96%) and enhanced stability (a 80% retention of initial performance after six cycles.), revealing the effective optimization and modulation between carbon nanotubes and iron particles. This excellent ODS activity originated from the defects of N-doped nanotubes as well as excellent particle dispersion and material transport capacity, which excites highly active free radicals with the assistance of H₂O₂. In addition, the unique two-dimensional tube channel and mesoporous structure promoted the diffusion and transfer of reactants and electrons, leading to high density of active sites. The different experimental conditions confirmed that the material is a bifunctional catalyst integrating adsorption and catalysis. This work provides an creative ideas for the rational design and synthesis of advanced ODS catalysts for fuel oil.     

Correlation of Water Vapor Permeability with Microstructure Characteristics of Building Materials Using Robust Chemometrics

This paper studies various microstructure parameters of natural and artificial building materials and aims to their correlation to the water vapor permeability. Three categories of building materials were investigated: stones, bricks, and plasters. Mercury intrusion porosimetry was applied in order to obtain the materials microstructure characteristics, a variety of pore size distributions and pore structure measurements, such as total porosity. The water vapor permeability of materials was determined experimentally according to ASTM standard E96-00. A robust principal component regression approach, coupled with multiple outlier detection, was applied in order to correlate water vapor permeability values to pore size distributions. A good quality correlation model was found by utilizing relative specific pore volume and relative specific pore surface distributions, whereas using pore structure measurements, such as total porosity, the correlation results were very poor. From the results, specific ranges of pore size distribution, corresponding to pores radius sizes greater than $10\,\upmu \text{ m }$ 10 μ m and between 1.778 and $0.421\,\upmu \text{ m }$ 0.421 μ m , contribute to the water vapor permeability of the materials.     

CATALYTIC CONVERSION OF MUNICIPAL WASTE PLASTIC INTO GASOLINE-RANGE PRODUCTS OVER MESOPOROUS MATERIALS

1. Introduction The recycling of polymer waste is important in the con- servation of resources and the protection of environment. Thermal degradation has been studied to characterize and determine the stability of polymers (Garforth et al., 1997). t Unfortunately, the products of thermal degradation from many polymers are distributed over wide ranges of carbon numbers and their commercial value is low, requiring up- grading for effective utilization. On the other hand, catalytic degradation o…     

Effect of surface/interface stress on the plastic deformation of nanoporous materials and nanocomposites

Surface and interface play an important role on the overall mechanical behaviors of nanostructured materials. We investigate the effect of surface/interface stress on the macroscopic plastic behaviors of nanoporous materials and nanocomposites, where both the surface/interface residual stress and surface/interface elasticity are taken into account. A new second-order moment nonlinear micromechanics theory is developed and then reduced to macroscopically isotropic materials. It is found that the effect of surface/interface residual stress is much more prominent than that of the surface/interface elasticity, causing strong size effect as well as asymmetric plastic deformation for tension and compression. The variation of yield strength is more prominent with smaller pore/inclusion size or higher pore/inclusion volume fraction. For a representative nanoporous aluminum, the surface effect becomes significant when the pore radius is smaller than about 50 nm. When hard inclusions are embedded in a ductile metal matrix, the interface effect and resulting size effect are much smaller than that of nanoporous materials. The results may be useful for evaluating the mechanical integrity of nanostructured materials.     

A phenomenological description of moisture capacity of iron ores

Moisture capacity of iron ore, defined as its ability to hold water, has been found to be affected by its particle size and chemical composition. To explain this phenomenon, mathematical model was developed on the basis of particle size, specific surface area, pore properties and contact angle between the iron ore and water. The specific surface area and the pore volume of iron ores were measured to validate the model, and parametric studies were carried out to investigate the effects of these factors, showing that particle size and surface area of the iron ore and thickness of the water film are the principal factors determining the moisture capacity. The model gave reasonable explanation of the phenomenon that moisture capacity increases with decreasing particle size. A correlation developed can well predict the moisture capacity of iron ores. Deviations between measurements and calculations were analyzed.     

Pore-structure-mediated hierarchical SAPO-34: Facile synthesis,tunable nanostructure,and catalysis applications for the conversion of dimethyl ether into olefins

Hierarchical cross-like SAPO-34 catalysts with different pore size distributions were obtained via hydrothermal synthesis with polyethylene glycol (PEG) as the mesopore-generating agent. The hierarchical SAPO-34 molecular sieves were characterized using X-ray diffraction, scanning electron microscopy, N₂ adsorption–desorption, thermogravimetric analysis, and temperature-programmed NH₃ desorption. The cross-like SAPO-34 catalysts exhibited enriched multi-porosity, and the sizes of their mesopores ranged from 10 to 50 nm. Both the mesoporous structures and morphologies of the hierarchical SAPO-34 could be further tuned through adjustments of the amount of PEG used. The as-obtained SAPO-34 showed dramatic catalytic performance in the conversion of dimethyl ether into olefins. A maximum selectivity of olefins of 96% was achieved, which was attributed to the rapid transport of the reactants and products in zeolitic micropores through mesopores.