Ben-Zu Wan

Pretreatment effect of gold/iron/zeolite-Y on carbon monoxide oxidation

A gold/iron/zeolite-Y catalyst was prepared by cation-exchange of iron-impregnated zeolite-Y with a chloroauric acid solution and subjected to various pretreatments prior to being used in carbon monoxide oxidation. The physical properties of the pretreated catalyst were characterized by X-ray powder diffraction, UV-Vis diffuse reflectance spectroscopy, temperature-programmed reduction and temperature-programmed desorption of carbon monoxide. By comparing to gold/zeolite-Y, the presence of iron oxide was found to hinder the sintering of gold metal during high-temperature treatment. The most active and water-durable catalyst was obtained by heating gold/iron/Y in a stream of humidified inert gas flow. The active sites on the catalyst were proposed to be gold hydroxide species surrounded by iron oxide.

Gold and iron supported on Y-type zeolite for carbon monoxide oxidation

Abstract Gold and iron supported on Y-type zeolite for carbon monoxide oxidation have been studied. They were prepared by ion exchange of gold(III) compounds with Y-type zeolite, iron-impregnated Y-type zeolite, or iron-exchanged Y-type zeolite in a chloroauric acid solution. The as-prepared gold/Y sample possessed high activity for carbon monoxide oxidation, but it gradually and irreversibly deactivated during the reaction. The deactivation was attributed to the transformation of some gold ions to gold metal. The activities of as-prepared gold/iron/Y samples were poor when compared with that of gold/Y, but their activities were markedly promoted by a high-temperature reduction treatment at 570°C. This is ascribed to the fact that the reduced gold/iron/Y catalyst could catch and release oxygen at low temperature.

Porosity Effects on Properties of Mesoporous Silica Low-k Films Prepared Using Tetraethylorthosilicate with Different Templates

A series of mesoporous silica films with different porosities and different pore sizes were prepared using different templates or different template concentrations in tetraethylorthosilicate colloid solutions. The amphiphilic templates such as cetyltrimethylammonium bromide (C 16 TMABr), Brij-56, Tween80, and Pluronic P123 were used. To investigate the effect of self-assembly surfactants on the film properties and to make a comparison, polyethylene glycol (molecular weight = 1450) which is not a surfactant was also used as a template in this research. Various film properties such as porosity, refractive index, dielectric constant, leakage current density, flatband voltage, hardness, and Youngs modulus were measured. For the film templated with C 16 TMABr, the high leakage current density and positive flatband voltage were attributed to the residual bromide in the framework, which was from bromine in C 16 TMABr after the calcination process. Moreover, its abnormally low dielectric constant was mainly due to the high leakage current density. For the films made with nonionic templates, the dielectric constant and the refractive index can be reduced linearly by increasing the film porosities; in other words, they are strongly related to the porosity rather than the pore size or the ordering of pore structure. However, the larger leakage current density and the weaker mechanical strength for more porous films are the drawbacks. According to higher values of flatband voltage, the elevation of leakage current densities are attributed to more silanol groups in the films. It was shown that the films with more ordered structures or thicker pore wall possessed better mechanical strength. Nevertheless, the porosity is the most influential factor upon mechanical strength of the films.

Nanoporous SiO2 films prepared by surfactant templating method - a novel antireflective coating technology

Abstract A sol-gel derived antireflection (AR) coating by surfactant templating method is presented. The spin coating process was used to deposit SiO 2 thin films on glass. The pore size and the pore volume of the film were controlled by the size and the volume of the template (i.e. Tween 80). It was found from this research that the transmittance was increased from 91.7% to above 99.0% either by a single-layer or by a double-layer porous SiO 2 antireflection coating, on both sides of the glass pane at a specific wavelength.

Gold supported on Ti incorporated MCM-36 as efficient catalysts in propylene epoxidation with H2 and O2

Novel catalysts consisting of gold nanoparticles (NPs) supported on the titanosilicate pillared MCM-36 (Si/Ti-MCM-36) with 2 nm mesopores were prepared. The influences of the Ti coordination environment on the particle size of the anchored Au NPs and their catalytic performances in propylene epoxidation with mixtures of H2 and O2 were investigated. The catalyst materials were characterized with Electron Probe Micro Analysis, X-ray diffraction, nitrogen sorption, UV-visible diffuse reflectance spectroscopy, transmission electron microscopy, and X-ray absorption spectroscopy. The coordination environment of Ti(IV) in Si/Ti-MCM-36 was found to be a mixture of octahedral (Oh) and tetrahedral (Td). The Au loading was proportional to the amount of Ti incorporated in the porous silica. The higher loading of Ti in Si/Ti-MCM-36 anchored more Au and resulted in the formation of larger Au particles. The deposition–precipitation (DP) with NH3 as a DP agent seemed to give Au NPs larger than those loaded by NaOH. The most efficient Au NPs size was about 1 nm, and Au NPs with sizes larger than 2 nm were not efficient for the propylene epoxide (PO) formation. By adjusting the Au and Ti synergy, the optimal PO formation rate over Au loaded Si/Ti-MCM-36 was 28.9 gPO h−1 gcat−1.

Reinforcing Porous Silica with Carbon Nanotubes to Enhance Mechanical Performance

In this study, porous silica (SiO2) film is reinforced with carbon nanotubes (CNTs), which gets homogeneously dispersed in porous SiO 2 gel by ultrasonic stirring. The size of SiO2 molecules is the same as that of nanotubes, so a fine CNTs/SiO2 network is formed. Nanoindenters used to test the mechanical properties of the resulting specimens show a marked enhancement in the properties as a function of filler content. Interfacial bonding and the distribution of CNTs also strongly affected the mechanical performance. Although a high concentration of CNTs improves the mechanical characteristics of the matrix, it also causes agglomeration such that the mechanical performance at the surface was disproportionate. Fourier transform infrared spectroscopy (FTIR) analysis indicates that there is little chemical reaction occurring between CNTs and SiO2. The results suggest that CNTs are ineffective reinforcements.

Low Dielectric Constant Silica Films Prepared by a Templating Method

He preparation of low dielectric constant porous silica films by a templating method was studied in this research, Several organic compounds (including ionic and non ionic surfactants), which can be dissolved in the coating solution, were used as the template. They were applied to make pores in the film by burning them off during calcinations in the air. TEOS (tetraethyl orthosilicate) was used as the silica source for the preparation of sol-gel. The processes that influenced the film thickness and the film surface modification were investigated. It was found from this research that the concentration of TEOS in the coating solution affected he film thickness the most. The spin speed during spin coating and the temperature increasing rate during the calcinations process only slightly influenced the thickness. The surface modification was most successful when the film was immersed in the limos (1,1,1,3,3,3hexamethyl disilazane) and toluene solution at 80°C. Moreover, for the templates tested in this research, it was found that the film using Tween 80 (polyoxyethylene(20) sorbitan monooleatel, a non-ionic surfactant) exhibited the lowest dielectric constant.

Porosity analysis of spin-on mesoporous silica films

The application of the surfactant-templated spin-on film as low- k or anti-reflection materials is strongly related to the porosity. Thus the pore structure was analyzed by the refractive index, the X-ray diffraction and the nitrogen adsorption/desorption in this research. Five types of templates were studied. The uniformity of all the film porosities was demonstrated by the very close refractive indices at different positions for each sample. The porosity in the films can be controlled by tuning the ratio of template/TEOS. The major mesopore size was observed to be related to the ratio of template/TEOS and the hydrophilic parts of different non-ionic surfactants. For the film made with PEG1450 (not a surfactant) as the template, both mesopores and micropores were found. However, the total pore volume was less than those made with non-ionic surfactants. The micelles formed by the amphiphilic molecules seemed to be better templates for making porous films.