Adsorption of diborane and hydrogen selenide on porous alumina and silica

Adsorption of diborane (B2H6) and hydrogen selenide (H2Se) on porous gamma-alumina and amorphous silica at room temperature were investigated. Both physical and chemical adsorption of H2Se on alumina were observed, while amorphous silica did not adsorb H2Se. Chemical adsorption of H2Se on alumina was accompanied by dissociation of H2Se to elemental Se. Diborane was adsorbed chemically on alumina and silica. The adsorption capacity of silica for B2H6 dramatically decreased after elimination of water molecules adsorbed on the surface by drying at about 100 degrees C in an N-2 atmosphere, although that of alumina was not changed by drying. Although B2H6 reacts with adsorbed water on alumina and silica surface, B2H6 is deduced to react with hydroxyl groups on alumina but not with those on silica. These observations are compatible with adsorption of various metal hydrides such as SiH4, AsH3 and PH3 on alumina and silica. The difference in the reactivity on metal hydride gases to gamma-alumina and silica can be related to the basicity of oxides and the proton affinity of hydrides. (C) 1998 Chapman & Hall.