Enhancement of enzymatic hydrolysis of corncob by microwave-assisted alkali pretreatment and its effect in morphology

Bioethanol produced from a conventional fermentation process using Saccharomyces cerevisiae utilizing pretreated and hydrolyzed corncob as a substrate was studied. It was found that the morphology of corncob was significantly changed after microwave-assisted alkali pretreatment was applied. An increase in the crystallinity index and surface area of the pretreated corncob was also observed. The highest total sugar concentration of 683.97 mg/g of pretreated corncob, or 45.60 g L^?1, was obtained from the optimum pretreatment conditions of 2 % NaOH at 100 °C for 30 min in a microwave oven. Microwave-assisted alkali pretreatment was an efficient way to improve the enzymatic hydrolysis accessibility of corncob in a shorter amount of time and at a lower temperature, compared to other methods.     

The use of alumatrane for the preparation of high‐surface‐area nickel aluminate and its activity for CO oxidation

Supported nickel has been used in a wide range of applications for industrial reactions, such as steam reforming, hydrogenation and methanation. In this work, nickel aluminate was prepared by the sol–gel process using alumatrane as the alkoxide precursor, directly synthesized from the reaction of inexpensive and available compounds, aluminum hydroxide and TIS (triisopropanolamine) via the oxide one pot synthesis (OOPS) process. Various conditions of the sol–gel process, such as pH, calcination temperature, hydrolysis ratio and ratio of nickel to aluminum, were studied. All samples were characterized using FTIR, TGA, XRD, TPR, DR‐UV and BET. The BET surface area was in the range of 340–450 m²/g at the calcination temperature of 500 °C with a mesoporous pore size distribution. Catalyst activity testing in CO oxidation reaction depended on Ni:Al ratio and calcination temperature. Higher activity was obtained from higher Ni content and lower calcination temperature. In addition, catalysts prepared using alumatrane precursor had higher percentage conversion than those prepared using aluminum hydroxide precursor. Copyright © 2005 John Wiley & Sons, Ltd.     

Photocatalytic membrane of a novel high surface area TiO2 synthesized from titanium triisopropanolamine precursor

Photocatalytic membrane was successfully prepared using an efficiently high surface area TiO₂ catalyst, dispersed into polyacrylonitrile matrix. The catalyst was directly synthesized using titanium triisopropanolamine as a precursor. The membranes were characterized using FT‐IR, TGA, SEM and their photocatalytic performance tested, viz. stability, permeate flux and photocatalytic degradation of 4‐NP. We find that polyacrylonitrile is an effective matrix, showing high stability and low permeate flux. The amount of TiO₂ loaded in the membrane was varied between 1, 3 and 5 wt% to explore the activity and stability of membranes in the photocatalytic reaction of 4‐NP. As expected, the higher the loading of TiO₂ loaded, the higher the resulting catalytic activity. Copyright © 2006 John Wiley & Sons, Ltd.     

Preparation of uniform and nano‐sized NaA zeolite using silatrane and alumatrane precursors

Nano‐sized Na A zeolite was successfully synthesized via the sol–gel process and microwave techniques. The synthesis parameters, such as hydroxide ion concentration, seed amount, as well as heating time and temperature, were studied to obtain the most uniform and very small sized NaA zeolite using the composition of SiO₂:Al₂O₃:xNa₂O:410H₂O; 3 ≤ x ≤ 6. It was found that hydroxide ion concentration affects the crystal size and heating time, whereas a higher amount of seed provides smaller sized NaA zeolite. The zeolite product can be synthesized using a higher temperature for a shorter time or lower temperature for a longer time. The best conditions for synthesizing the smallest size, 0.1–0.2 µm, and the most homogeneous NaA zeolite is to use the composition of SiO₂:Al₂O₃:3Na₂O:410H₂O and 3 wt% crystal seed at 80 °C microwave heating for 6 h. The synthesized NaA zeolite was characterized using XRD and SEM. Copyright © 2006 John Wiley & Sons, Ltd.     

Effects of synthesis parameters on zeolite membrane formation and performance by microwave technique

Recently, zeolite membranes on porous supports have been extensively studied in the ethanol–water separation process for further use for gasohol production. This work focuses on a NaA membrane synthesized on an α‐Al₂O₃ support via microwave hydrothermal treatment. Synthesis temperature and time, type of substrate, seed amount and seeding time for the layer growth of the membrane are considered. The formation of as‐synthesized membranes is discussed according to observations by SEM and XRD. In addition, a preliminary study of the performance of the synthesized NaA zeolite membrane was conducted using the pervaporation technique. It was found that, for the synthesized continuous NaA membranes prepared using a 0.5 µm NaA crystal seed concentration of 3 g/l via vacuum seeding, the optimum conditions were 363 K synthesis temperature for 15–20 min via microwave heating. The flux and the separation factor obtained were 1.6 kg/m² h and 1760.5, respectively, for the substrate without an intermediate layer. Interestingly, the substrate with an intermediate layer showed better flux and separation factor at 1.7 kg/m² h and 6532.7, respectively. Copyright © 2007 John Wiley & Sons, Ltd.     

A novel route to perovskite lead zirconate from lead glycolate and sodium tris(glycozirconate) via the sol–gel process

A perovskite lead zirconate was synthesized, using lead glycolate and sodium tris (glycozirconate) as the starting precursors, by the sol–gel process. The obtained molar ratio Pb:Zr of PbZrO₃ was 0.9805:1. The TGA–DSC characterizations indicated that the percentage of ceramic yield was 56.4, close to the calculated chemical composition of 59.6. The exothermic peak occurred at 245.7 °C, close to the theoretical Curie temperature of 230 °C. The pyrolysis of PbZrO₃ of the perovskite phase was investigated in terms of calcination temperature and time. The structure obtained was the orthorhombic form when calcined at low temperature at 300 °C for 1 h; it transformed to the monoclinic and cubic forms of the perovskite phase at higher temperatures above the Curie temperature as verified by X‐ray data. The lead zirconate synthesized and calcined at 300 °C for 1 h has the highest dielectric constant, the highest electrical conductivity and the dielectric loss tangent of 2267, 3.058 × 10^?4 (Ω m)^?1 and 2.484 at 1000 Hz, respectively. The lead zirconate powder produced has potential applications as materials used in microelectronics and microelectromechanical systems. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of Fe‐loaded MFI zeolite using silatrane as precursor and its CO activity

Fe‐MFI zeolite was successfully synthesized using silatrane as precursor and tetrapropyl ammonium bromide as template via the sol–gel process and microwave heating technique. The effects of ageing time, heating temperature, heating time and iron concentration were investigated, and it was found that Fe‐MFI synthesis favors higher heating temperatures, but is limited by the degradation of the incorporation of a template molecule. Moreover, longer ageing and heating times promote the incorporation of higher amounts of iron atom in the MFI structure. However, too long an ageing time decreases the incorporation of iron. The lower the percentage Fe loading, the greater the percentage of Fe³⁺ ions incorporated into the MFI framework. The catalytic activity of Fe‐MFI catalyst for the oxidation of CO was studied and it was found that these synthesized catalysts catalyzed the oxidation of CO very well. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis of Fe‐MCM‐41 from silatrane and FeCl3 via sol–gel process and its epoxidation acivity

An iron‐containing mesoporous molecular sieve, or Fe‐MCM‐41, was successfully synthesized the via sol–gel technique using silatrane and FeCl₃ as the silicon and iron sources, and was characterized using various techniques. Many factors were investigated, namely, reaction temperature and time, calcination rate, and iron amount in the reaction mixture. It was found that the optimum conditions in which to synthesize Fe‐MCM‐41 was to carry out the reaction at 60 °C for 7 h using a 1 °C min^?1 calcination rate and a 550 °C calcination temperature. The catalytic activity and selectivity of styrene epoxidation using hydrogen peroxide showed that the selectivity of the styrene oxide reached 65% at a styrene conversion of 22% over the 1%wt catalyst. Copyright © 2008 John Wiley & Sons, Ltd.