Surface reconstruction, modification and functionalization of natural diatomites for miniaturization of shaped heterogeneous catalysts

Abstract

Since the discovery of mesoporous silica in 1990s, there have been numerous mesoporous silica-based nanomaterials developed for catalytic applications, aiming at enhanced catalytic activity and stability. Recently, there have also been considerable interests in endowing them with hierarchical porosities to overcome the diffusional limitation for those with long unimodal channels. Present processes of making mesoporous silica largely rely on chemical sources which are relatively expensive and impose environmental concerns on their processes. In this regard, it is desirable to develop hierarchical silica supports from natural minerals. Herein, we present a series of work on surface reconstruction, modification, and functionalization to produce diatomite-based catalysts with original morphology and macro-meso-micro porosities and to test their suitability as catalyst supports for both liquid- and gas-phase reactions. Two wet-chemical routes were developed to introduce mesoporosity to both amorphous and crystalline diatomites. Importantly, we have used computational modeling to affirm that the diatomite morphology can improve catalytic performance based on fluid dynamics simulations. Thus, one could obtain this type of catalysts from numerous natural diatoms that have inherently intricate morphologies and shapes in micrometer scale. In principle, such catalytic nanocomposites acting as miniaturized industrial catalysts could be employed in microfluidic reactors for process intensification.