Silylation of layered silicate RUB-51 with SiCl₄ and conversion of the silylated derivative to a crystalline microporous material

A novel crystalline microporous material is synthesized by silylation of layered silicate RUB-51 with tetrachlorosilane (SiCl₄), hydrolysis, and heat treatment for interlayer condensation. One SiCl₄ molecule first undergoes ordered silylation with two confronting groups, Si-O^- and Si-OH, on the interlayer surfaces of RUB-51 (bidentate silylation). Hydrolysis of the unreacted Si-Cl groups of the immobilized silyl groups by a mixture of H₂O and dimethyl sulfoxide (DMSO) affords geminal Si-OH groups on the surfaces without simultaneous interlayer condensation because of intercalation with DMSO. Subsequent heat treatment leads to condensation between neighboring layers, and the condensed material is composed of layers of RUB-51 displaced by a half-unit cell along the a axis. Hydroxyl groups are present after interlayer cross-linking, which is one of the unique features of the method using SiCl₄. The obtained sample adsorbs CO₂ molecules, while RUB-51 itself without silylation cannot. The amount of adsorbed CO₂ on the microporous material is larger than that of CH ₄, suggesting the potential of this material as a separation medium between CO₂ and CH₄. This study indicates that the preparation of microporous materials, using layered silicates as a building block and various silylating agents, is useful for precise design of both porosity and functional groups on pore surfaces, which drastically affect the properties of crystalline microporous materials, including catalytic selectivity and separation capability.