Aerosol assisted synthesis of nanostructured silica

Abstract

Zeolites are microporous aluminosilicates that have broad applications especially in industrial processes like fluidized catalytic cracking (FCC) owing to their unique properties with respect to both activity and selectivity. However, the micropores of zeolites may in some cases limit their catalytic performance due to restricted molecular transport induced by similar size of the diffusing hydrocarbons and the micropore size. This had led researchers to develop mesoporous silica materials (pore sizes in the range of 2 and 50 nm) as catalyst supports for enhanced molecular transport. Mesoporous silica are usually prepared using the conventional sol-gel synthesis which takes several days and the final morphology is often irregular. The present thesis deals with the use of a continuous aerosol reactor process involving evaporation induced self-assembly (EISA) that allows synthesis of mesoporous silica (using a tri-block co-polymer, P123 as a templating agent) within several seconds. The synthesis in general involves a large number of experimental parameters. In order to explore this high dimensional experimental space, a factorial design of experiments was employed to study the effect of important variables, namely the precursor composition and the tubular reactor temperature, on the textural properties of the final product. This methodology allows simultaneous investigation of the influence of multiple parameters, which is advantageous over the traditional form of experimentation in the nanomaterials community, where only one variable is changed at a time. It allows exploration over a wider range of conditions to highlight the true nature (global/local) of trends that are often misinterpreted as a universal occurrence in conventional experimental trials. Using contours, this method exclusively determined multiple conditions for achieving a required surface area and pore volume. It also illustrated the variation of these properties over a wider domain of experimental conditions. Additionally, novel mesoporous silica and silica-alumina materials were synthesized using a laboratory spray drier by self-assembly of nanosized silica and alumina particles, using P123 as a structure directing agent. The materials possessed extraordinary steam stability and showed good potential when their performance was tested in pulse cracking experiments. The method offers exciting opportunities for further industrial development as part of mesoporous zeolite composites.Applied Science