Macroporosity Control by Phase Separation in Sol-Gel Derived Monoliths and Microspheres

Macroporous and hierarchically macro/mesoporous materials (mostly monoliths and microspheres) have attracted much attention for a variety of applications, such as supporting or enabling materials in chromatography, energy storage and conversion, catalysis, biomedical devices, drug delivery systems, and environmental remediation. A well-succeeded method to obtain these tailored porous materials relies on the sol-gel technique, combined with phase separation by spinodal decomposition, and involves as well emulsification as a soft template, in the case of the synthesis of porous microspheres. Significant advancements have been witnessed, in terms of synthesis methodologies optimized either for the use of alkoxides or metal-salts and material design, including the grafting or immobilization of a specific species (or nanoparticles) to enable the most recent trends in technological applications, such as photocatalysis. In this context, the evolution, in terms of material composition and synthesis strategies, is discussed in a concerted fashion in this review, with the goal of inspiring new improvements and breakthroughs in the framework of porous materials.

A Research on Preparation and Application of the Monolithic Catalyst with Interconnecting Pore Structure

In recent years, the monolithic material has been developed increasingly in the high performance liquid phase field, and it could also be applied in the field of catalyst, as a monolithic catalyst carrier, since it has a large specific surface area, and could be customized based on the mould. The monolithic catalyst is characterized with many advantages such as low bed pressure, high physical efficiency and small amplification effect. The most impotant part refers to the preparation of copper-based catalyst. The impregnation method is used to produce CuO-ZnO monolithic catalyst and CuO-ZnO-ZrO₂ monolithic catalyst with the prepared monolithic silica-alumina carrier. The fixed bed microreactor is used to investigate the effect of copper-based catalyst on the process in which carbon dioxide is used to produce methanol through hydrogenation. The metal salt is added into the sol-gel process, which could form the M-O-Si bond, thus make the metal-containing catalytic material obtain good mechanical strength, and make it possible to be introduced into the acidic center generally. The metal-containing catalytic material carrier also has macropores and mesopores. The presence of large pores could make the molecular mass transfer more effective, while the presence of mesopores could increase the specific surface area of the material. In this paper, the experimental study has been conducted on the production of methanol through hydrogenation of CO₂ under different catalysts, to mainly investigate the effect of catalysts with different catalytic performance on the reaction.

First acidic macro-mesocellular aluminosilicate monolithic foams “SiAl(HIPE)” and their catalytic properties

A new type of macrocellular and mesoporous acidic aluminosilicate monolithic foam obtained by a templated alkaline sol–gel route exhibits high dehydration activity.

Sol–gel synthesis of Ni and Ni supported catalysts for hydrogen production by methane decomposition

Sol-gel synthesis of NiO and supported NiO catalysts for hydrogen production by methane decomposition.

Catalytic cracking of large molecules over hierarchical zeolites

A hierarchical zeolite catalyst was synthesized by transforming the skeletons of a bimodal pore silica gel into a zeolite through a steam-assisted conversion method, and shows high catalytic activity and a long catalyst lifetime for catalytic cracking of large molecules.

Electrokinetic Effects on the Transport of Charged Analytes in Biporous Media with Discrete Ion-Permselective Regions

The influence of external electrical fields on local concentration distributions and the mass transport of ionic background (buffer) species, as well as eluting co- and counterionic tracer molecules, was investigated in a fixed bed of native glass beads by confocal laser scanning microscopy and numerical simulations. Due to the negative surface charge of the porous glass beads and significant electrical double layer overlap, the intraparticle mesopore space becomes ion-permselective. This cation selectivity and the externally superimposed electrical fields induce concentration polarization in the bulk electrolyte solution adjacent to the particles. At the anodic hemisphere of a bead, the actual interplay of convection, diffusion, and electromigration leads to the formation of a convective-diffusion boundary layer with reduced ion concentrations relative to the bulk solution. At the opposite, cathodic hemisphere where counterions leave a bead in the direction of the applied field, electrolyte concentrations increase generating an enriched concentration polarization zone. Complementary data from quantitative confocal laser scanning microscopy and numerical simulations provide insight into the spatial variations of chemical and electrical potential gradients in the hierarchically structured material, including molar flux densities of the background ionic species, and reveal the elution dynamics of co- and counterionic analytes. These results demonstrate that concentration polarization in the external fluid domain, as well as the magnitude and sign of electrophoretic with respect to electroosmotic mobility in the ion-permselective domain, are major local contributions to coupled mass and charge transport, reflecting analyte retention, migration, and dispersion on a macroscopic scale.