Effect of Nanoparticulate Boehmite Sol in γ-Alumina Coating on a Metal Surface as a Catalyst Support for Micro Channel Reactors

Micro channel reactors can, to a large extent, eliminate the problems of fixed bed reactors such as pressure drop, hot and cold spots. Methanol steam reforming by employing micro reactor technology is among the best ways for on-board hydrogen production for fuel cells. By this waystorage and handling problems of hydrogen are not necessary. However, using ceramic micro channel reactor is not suitable for supplying large amount of heat required for the highly endothermic reaction of methanol steam reforming, due to low thermal conductivity of ceramic material as compared to metals. Therefore, metal structured micro channel reactors are introduced for these sorts of applications. But smooth surface of metals has very low surfaceareas which are not suitable as a catalyst support. Thus, metal surfaces must be coated by a porous material such as γ-alumina to increase their specific surface areas by a factor of about 10. Adherence of ceramic material such as γ-alumina to the metal surface is a difficult challengethough. In this paper, surfaces of aluminum and stainless steel were degreased and ultrasonically cleaned in acetone. As a first method, γ-alumina was deposited on the metal surfaces by dip coating in a γ-alumina suspension, followed by drying and calcining at 600oC. Inthe second procedure micro sized boehmite are suspended in a diluted nitric acid solution containing γ-alumina particles. In this way the sol of boehmite are formed, aged overnight to get polymerized and produce nanosized boehmite, which encompass γ-alumina particles. Themetals are then dip coated in this gel-like suspension and heat treated similar to the first procedure. The weight loss through the ultrasonic wave and dropping of the coated sample from a given height to the ground for two methods was compared. The results show that the second method is better than first one and boehmite nanoparticulate sol can improve the adherence of Alumina to the metal surfaces.

Keywords:

Nanoparticulate Boehmite Sol , γ-Alumina , Metal Coating