Synthesis, Characterization, And Catalytic Properties Of Hierarchical Porous Materials

Porous materials with high surface areas and pore volumes are of interest for energy storage, separation, catalysis, and other applications. However, the applications of porous materials are sometimes significantly influenced by their sole porosity and complex and costly synthesis. It is highly desirable to develop facile routes to hierarchical porous materials, combining advantages of multi-porosity. The hierarchical porous structure with high diffusion, surface area, and pore volume will lead to their high accessibility and high storage capacity in many possible applications.The aims of the present project are: (1) to develop facile, low cost and efficient routes to novel hierarchical porous materials such as carbon, zeolites, silica, metal oxide; (2) to characterize the structure and properties of hierarchical porous materials. To elucidate the specific formation mechanism and interaction factors during the synthetic system; (3) to investigate the applicability of hierarchical porous materials to catalysis.Solid crystals of zeolites with intricate micropores have been widely used in industry as heterogeneous catalysts, in particular as solid acid catalysts in the fields of oil refining and petrochemistry. However, relatively small and sole micropores in zeolites such as Beta, ZSM-5, and Y strongly influence the mass transport to and from the active sites located in micropores, which severely limit the performance of industrial catalysts. To overcome this limitation, various strategies such as synthesis of nanosized zeolites, invention of various ultralarge-pore zeolites and zeolite analogues, and ordered mesoporous materials have been successfully pursued. However, the use of these novel materials is rather limited, because of the difficult separation of nanosized zeolite crystals from a reaction mixture, the complexity of the templates used for the synthesis of ultralarge-pore zeolites, and the relatively low thermal and hydrothermal stability of ordered mesoporous materials. More recently, mesoporous zeolites from nanosized carbon templates have been also successfully synthesized, but their industrial applications are still limited by the complexity of synthetic procedure and hydrophobicity of carbon templates. We demonstrate here a unique, facile, controllable, and universal route for the synthesis of hierarchical mesoporous zeolites templated from a mixture of small organic ammonium and cationic polymer. Obviously, the synthesis of hierarchical mesoporous zeolites is easily controlled. More importantly, these novel zeolites exhibit excellently catalytic properties, compared with conventional zeolites.Porous carbon materials with high surface areas and pore volumes are of interest for energy storage, separation, catalysis, and other applications. Currently there is a tendency to use nanocasting method for producing carbon materials. Various template syntheses of porous carbon materials have been successfully studied. Microporous carbons are templated from zeolite Y, Beta nanochannels; Ordered mesoporous carbons are templated from ordered mesoporous silica such as MCM-48 and SBA-15; Macroporous carbons are templated from silica and polystyrene spheres; More recently, facile surfactant directed synthesis of mesoporous carbon has been reported. On the other hand, due to the rapid mass transport and pressure drop reduction, porous carbons with high surface areas, larger pore diameters, and hierarchical pores have received considerable attentions in many applications such as catalysis, purification, and chromatography. Hierarchical porous carbons are generally synthesized using hierarchical porous silica as template or multi-templates. However, the wide application and large-scale synthesis of porous carbon materials are still faced challenge because of the complex and time-consuming operation, formation of nonporous carbon on external surface of the template, incomplete infiltration of carbon precursors, template costs, and limited synthetic conditions. Herein, we use a simple and efficient ion change infiltration route to synthesize hierarchical porous carbon (HC) materials with tri-model porosity from an industrial ion exchange resin as carbon precursors and silica as hard template. For the strong recognition between the host and guest, the infiltration is one step and short time, the precise control is avoided. For the simple operation and industrial resin, the synthesis is low cost and easily scaled up. The obtained HC sample shows a good performance on oxidative dehydrogenation of ethylbenzene to styrene even at the low temperature. Besides, we obtained hierarchical porous aluminosilicates after removal of resin in resin/silica composite by calcination.Furthermore, we demonstrated a simple and environmentally benign preparation of honeycomb-like macrostructured and microporous carbon materials from microwave popping and thermal carbonization of maize. Steaming explosion in the maize under microwave radiation is a key factor for the formation of macrostructure and microposity. The prepared carbon materials show adjustable pore volumes and surface areas, as well as a high catalytic performance on oxidative dehydrogenation of ethylbenzene to styrene.One-dimensional nanostructures in nanotechnology have received enormous interest for their fascinating physical properties and numerous potential applications. Typically, silica nanotubes (SNT) are biocompatible, photoluminescent, and accessible. They have been extensively applied to many fields of science and technology, such as catalysis, optics, bioseparation, biosensor, nanoscale electronics, and storage and delivery system. Particularly, mesostructured silica tubes are recently fabricated by liquid-crystal phase transformation, templating anodic alumina and polycarbonate membranes for their unique combination of mesostructure and one-dimensionality. However, most syntheses are complicated and multi-steps, and the obtained tube diameters are from hundreds of nanometers to micrometer. It is highly desirable and challenging to achieve mesostructured silica nanotube less than 100 nm through a facile route for their fascinating properties from nanosize.On the other hand, carbon nanotubes (CNT) have been extensively applied to fabrication of nano-composites and nano-device for their unique electronic and mechanical properties. These applications are sometimes limited by the chemical inertness and poor compatibility of CNT. To promote the compatibility and dispersion of CNT, progresses have been recently achieved by coating CNT with modifiable silica surface. However, there is still no CNT coated with mesostructured silica.Herein, we report one-pot hydrothermal route to mesostructured silica nanotubes from the assembly of CNT, CTAB, and silica gel, followed by the calcination. The synthetic procedure is simple and the obtained silica nanotubes show very small tube diameters, uniformed mesopores, and huge pore volume. Besides, mesostructured silica coated CNT composite is obtained by removal of CTAB in NH4NO3/ethanol mixture, which not only facilitate the incorporation of CNT in functional composites, but also provide a route to addressable CNT devices potential for sensor and device structures.