2006 Volume 39 Issue 5 Pages 503-512
The aim of this work is to develop a high performance heat exchanger type reactor with plate catalysts for proton exchange membrane fuel cell (PEMFC) systems and other applications. Steam reforming of ethanol using silica-coated alumite catalysts on aluminum plates (JIS A3003) was performed in a preliminary study at atmospheric pressure in a temperature range of 300–600°C using a plug flow reactor. Alumite catalysts, prepared by anodic oxidation of aluminum plates, are advantageous for the endothermic reaction of steam reforming because of their good thermal conductivity. However, in an ethanol steam reforming test performed with an alumite support (γ-Al2O3/Al plate) or an alumite catalyst (Ni/γ-Al2O3/Al plate), ethylene was produced as the main byproduct because of the dehydration reaction of ethanol. In order to inhibit ethylene formation, silica-coated alumite supports (Silica/Al2O3/Al plate) and silica-coated alumite catalysts (Ni/Silica/Al2O3/Al plate) were prepared using two types of silica sols with different particle size. As a result, the formation of ethylene (C2H4) under a condition of the same apparent support/catalyst surface area was reduced dramatically with both the silica-coated alumite supports and the silica-coated alumite catalysts. For example, with the silica-coated alumite catalyst (Ni/Silica/Al2O3/Al plate) prepared with a silica sol having a smaller particle size (particle diameter: 8–11 nm), C2H4 was reduced by 88% at 450°C, by 45% at 500°C and by 57% at 550°C compared with the levels seen for the alumite catalyst (Ni/γ-Al2O3/Al plate). A temperature programmed desorption analysis with ammonia desorption showed that the number of acidic sites per apparent surface area of the silica-coated alumite supports and the silica-coated alumite catalysts was smaller than that of the alumite support and that of the alumite catalyst without any silica coating. These results suggest that the low level of ethylene formation seen for both the silica-coated alumite supports and silica-coated alumite catalysts can be attributed to the smaller number of acidic sites. It is concluded that the silica-coating method is preferable for improving the properties of alumite supports and alumite catalysts for ethanol steam reforming.
