日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Sepiolite is a fibrous magnesia-silicate clay mineral. The idealized formula for the structure of this mineral is Mg₈Si₁₂O₃₀(OH)₄(H₂O)₄6-8H₂O and the crystal contains uniform size parallelpiped intracrystalline tunnels along the fiber and their cross section is about 1.35×0.67 nm². The zeolitic water and coordinated water molecules are contained in the tunnel. As sepiolite can provide a restricted field for reactions as like as zeolite, it can be used to shape selective catalyst with high selectivity such as cyclodehydration of diethyleneglycol. The Mg²⁺ ions located at the edge of the octahedral sheet which form the walls of the tunnels along the fiber are exchangeable with various alkaline and transition metal cations. Sepiolite is active for the demetalation from petroleum.Sepiolite can be used as the catalyst for dehydration of alcohol, because it provide Lewis acidic sites by releasing a coordinated water from Mg²⁺ located at the tunnel wall. Broensted acidic sites are formed by substituting Mg²⁺ located at the tunnel wall Al³⁺. While basic site are formed by substituting with alkaline cation such as Li⁺, Na⁺, K⁺ and Cs⁺. The sepiolite substituted Mg²⁺ by transition metal ions behaves as an acid-base bifunctional catalyst for the conversion of ethanol to 1,3-butadiene. Sepiolite is an effective support of the catalyst for preparing fine particles of metals. The reaction od positron in the tunnels of sepiolite is interesting as a new tool to investigate microporous material.