Mesoporous Silica Nanomaterials Applications in Catalysis

Abstract

Mesoporous silica materials benefit from unique features that have attracted substantial interest for their use as catalyst-immobilization matrices. These features include high surface area, chemical, thermal, and mechanical stability, highly uniform pore distribution and tunable pore size, high adsorption capacity, and an ordered porous network for free diffusion of substrates and reaction products. Solid supported catalysts are of great interests in both academic and industrial arenas due to their recyclability, enhanced catalytic reactivity, and selectivity. Inorganic, organic end enzymatic catalysis fields have been revolutionized by introduction of mesoporous silica nanomaterials as support due to dramatic increase of contact area and thus contributing to overall reaction yield [1-4]. Furthermore, mesoporous silica offers the opportunity of multifunctionalization and therefore, multiple catalyst immobilizations. The ability to sequester selectively molecules buy their functionality makes mesoporous silica catalyst championing high selectivities. This editorial will highlight the most important achievements in the field of mesoporous silica-supported catalysis. The first mesoporous silica material was first reported as early as 1971, where a material described as low-bulk density silica was obtained from hydrolyzing and condensing tetraethoxysilicate (TEOS) in the presence of cationic surfactants [5]. This result did not gain much attention at the time it was published because the porosity and structural properties were not reported. It was not until 1992 that the chemistry society started to realize the potential of this field, when scientists in oil giant Mobil Corporation laboratories published a series of ordered mesoporous materials (M41S) with pore sizes ranging from 1.5-10 nm. The variant called MCM-41 with 1000 m 2 g -1 and pore volumes up to 1 cm 3 g -1 , has been comprehensively studied and widely applied in many fields such as drug delivery, biosensors and catalysis [6-12]. The morphological transformations that lead to converting bulk MCM-41 mesoporous silica to functionalized mesoporous silica nanospheres (MSNs) by Lin’s group represented a step forward toward increasing control of kinetics in catalytic reactions occurring in functionalized MSN [10]. The first report of utilizing mesoporous silica in polymer synthesis catalysts initiated by Aida’s group in Japan, has opened new avenues toward modern solid-supported catalysis. The authors reported crystalline nanofibers of linear polyethylene with an ultrahigh molecular weight (6,200,000) and a diameter of 30 to 50 nanometers, formed by the polymerization of ethylene with mesoporous silica fiber–supported titanocene, with methylalumoxane as a cocatalyst. Small-angle x-ray scattering analysis indicated that the polyethylene fibers consist predominantly of extended-chain crystals. The Science article highlighted the potential utility of the honeycomb-like porous framework as an extruder for nanofabrication of polymeric materials [13].