MICROPOROUS MIXED OCTAHEDRAL-PENTAHEDRAL-TETRAHEDRAL FRAMEWORK SILICATES

Abstract

The frameworks of zeolites and related crystalline microporous oxide materials, such as aluminophosphates, silicoaluminophosphates and metaloaluminophosphates, are built up of tetrahedrally coordinated (e.g., Si, Al, P) atoms. Microporous structures comprised entirely of octahedral sites are also known, encompassing manganese oxides and phases with composition Na2Nb 2íxMxO 6íx(OH)x H 2O, where M = Ti, Zr, and 0< x 0.4. Mixed octahedral-pentahedral-tetrahedral microporous (OPT) siliceous frameworks have been much studied since the early 1990s. Comprehensive research into synthetic OPT materials was initiated by the seminal contributions of Kuznicki (titanosilicates ETS-4 and ETS-10), (ETS-4, and titanosilicate analogues of minerals vinogradovite and pharmacosiderite) and (ETS-10), and the early work of the groups of Raveau (tantalo and niobosilicates), (stannosilicates).