Silica phase behavior and the formation of microporous and mesoporous materials

Over the last 10 years, the chemical industry has begun a shift from economies of scale to targeted production of chemicals at the final user. Targeting chemical production eliminates the expenses of transportation, of operating and maintaining large scale plants, and of managing safety and environmental issues often associated with large-scale hazardous chemical production. This decrease in production scale has led to a reevaluation of many current chemical processes. The reaction and separation unit operations developed to succeed at large scales often cannot operate in targeted systems. Zeolites and mesoporous materials are one solution to scaling down these processes.; For reaction systems, zeolites, crystalline aluminosilicate materials, act as novel catalysts and supports. Zeolites have pore sizes ranging from 5 to 13 A with catalytic sites located primarily within the materials pores. These properties enable zeolites to perform both separation and reaction processes simultaneously often leading to higher selectivities than conventional catalysts. The one drawback of zeolites is that their small pore size limits their applications to systems containing small molecules. For large molecule systems, mesoporous silicates, porous amorphous silicates with pore sizes ranging from 2 to 10 nm, are often viable separation alternatives.; Over a hundred zeolite and mesoporous materials have been synthesized with many finding a role in commercial applications; but in some respects, the number of current applications is well below that expected for materials with such ideal separation properties. The limiting factor in developing useful zeolites and mesoporous materials has been the inability to effectively understand the synthesis of these materials. Particularly, no framework has been developed which can predict a priori the zeolite crystal or mesoporous framework formed, the final particle morphologies, and the final material composition. Each of these characteristics significantly impacts the catalytic and separation properties of the material. In this work, we begin to develop a framework for understanding the initial stages of zeolite and mesoporous material formation for the development of novel silica materials by 'design'.; We focus on understanding the behavior of silica at room temperature in the precursor 'homogeneous' solutions that lead to zeolites or mesoporous solids. These solutions consist of five components silica, water, hydroxide ions (the mineralizing agent), and either organic or inorganic cations, which are involved in determining the final zeolite crystal or mesoporous material framework, and alumina. (Abstract shortened by UMI.)...