Thermally stable alumina–gallia aerogel as a catalyst for NO reduction with C3H6 in the presence of excess oxygen

In order to improve thermal stability, an alumina–gallia aerogel was prepared and the catalyst performance for NO reduction with C₃H₆ was compared with that of an alumina–gallia xerogel. Basically, both were prepared by a sol–gel method with supercritical drying for the former, while with oven drying for the latter. Upon heating at 800, 900, and 1000°C, the aerogel exhibited higher NO conversion than the xerogel at reaction temperature <400°C, while NO conversion was lower on the former than on the latter at >500°C. At 450°C, NO conversion was almost the same for these two catalysts. A marked difference was observed upon heating them at 1100°C: the aerogel still maintained quite a high activity, while the xerogel greatly lost it. After heating the aerogel at 1100°C, -phase alumina remained untransformed with its surface area of 80 m²/g, while the xerogel was completely transformed to -alumina with its surface area of 6 m²/g. The high activity remaining on the aerogel heated at 1100°C was ascribed to its large surface area.     

Combustion behavior and application of polyolefin‐based floor sheet laminated with Nylon‐6/clay nanocomposites film

Nanocomposites are potential materials that can be used to improve the flame resistance of polymers without the need for halogen‐based flame retardants. However, the nanocomposites cannot be used as the only raw material to produce final products as they are too expensive compared with low‐cost commodity plastics. Therefore, some types of polyolefin‐based floor sheet laminated with nanocomposites film were prepared for the cone calorimetric study to determine the suitable nanocomposites laminated structure for flame resistance. This study found that the polyolefin‐based floor sheet laminated with 200 µm Nylon‐6/montmorillonite nanocomposites film on the surface can reduce the HRR _max and the S significantly; other types of nanocomposites film‐laminated floor sheet were not able to reduce their flame resistance in comparison with the normal Nylon‐6 film‐laminated floor sheet. Meanwhile, based on the gas barrier performance, the higher aspect ratio of clay is assumed to contribute to the higher flame resistance of nanocomposites. Thus, the polyolefin‐based floor sheet laminated with Nylon‐6/sericite nanocomposites film on the surface was also prepared and examined in the cone calorimetric study. However, the Nylon‐6/sericite nanocomposites film surface‐laminated floor sheet did not cause a significant reduction in the HRR _max and S compared with the Nylon‐6/montmorillonite nanocomposites film surface‐laminated floor sheet. The grade determined according to the standard fire test and the mechanical properties of the Nylon‐6/montmorillonite nanocomposites film surface‐laminated floor sheet satisfied the requirements for floor sheets for Japanese railway vehicles. Copyright © 2010 John Wiley & Sons, Ltd.     

Catalytic reduction of NO by hydrocarbons over a mechanical mixture of spinel Ni–Ga oxide and manganese oxide

NO reduction with propylene over Mn₂O₃, spinel Ni–Ga oxide and their mechanical mixtures has been investigated. Mn₂O₃ has no activity to NO reduction, but has a high activity for NO oxidation to NO₂. Spinel Ni–Ga oxide showed an apparent activity to NO reduction only at temperatures above 400°C. Mixing of Mn₂O₃ to the Ni–Ga oxide resulted in a significant enhancement of NO reduction in the temperature range of 250–450°C. The optimal Mn₂O₃ content in the mixture catalyst was about 10–20 wt%. It is suggested that the synergetic effect of Mn₂O₃ and Ni–Ga oxide plays an important role in the catalysis of NO reduction. The Ni–Ga oxide and Mn₂O₃ mixture catalyst is superior to Pt/Al₂O₃ and Cu-ZSM-5 by showing a higher NO reduction conversion, resistance to water and negligible harmful by-product formation. Other lower hydrocarbons C₂H₄, C₂H₆ and C₃H₈ also give a maximum NO reduction conversion as high as 50%. The difference from using C₃H₆ is that the temperature at the maximum NO reduction is higher than it is with C₃H₆. This revised version was published online in July 2006 with corrections to the Cover Date.     

A novel alumina catalyst support with high thermal stability derived from silica-modified alumina aerogel

A new alumina catalyst support with high thermal stability was synthesized. The high thermal stability was achieved through the synergetic effect of silica addition and the ultra-low bulk density (aerogel). The amount of silica was varied from 2.5 to 10 wt% and 5 wt% was found to be most effective for suppressing phase transformation; the θ phase remained even after heating at 1400°C for 1 h. The surface areas of the present alumina with 5 wt% silica were 86 and 36 m²/g after heating at 1300 and at 1400°C, respectively. This revised version was published online in November 2006 with corrections to the Cover Date.     

Improvement of thermal stability of alumina by addition of zirconia

To maintain a large surface area at elevated temperatures, zirconia was added to transition alumina. The addition of a small amount of zirconia resulted in a marked suppression of phase transformation from θ- to α-alumina. After heating at 1200°C, ZrO₂‐containing alumina exhibited a large surface area of 50 m₂/g. UV‐VIS and XRD measurements indicated that zirconia existed in a high dispersion state after calcining at 800°C. XPS measurement also showed that zirconia existed as monolayer. Zirconia monolayers are concluded to cover the alumina surface and the interaction between them may be the cause for the suppression of phase transformation and also for the maintenance of the large surface area at elevated temperatures. The interaction remains up to 1200°C, therefore, θ phase remained at 1200°C. This revised version was published online in July 2006 with corrections to the Cover Date.