Thiol-functional porous silica spheres with 100-μm mean diameter were synthesized in
one quick step for ca. 60 min at room temperature using 1-alkylamine templating through
the S+X-I+ assembly pathway under an acidic condition. Thiol groups were introduced into
materials while mesoporous silica spheres were prepared. SEM observation revealed that
dodecylamine templating afforded a higher particle-shape quality than octylamine templating. Pore size and surface hydrophilicity of organic-functional silica spheres systematically
decreased with increasing coverage of thiol groups on the pore surface, but the specific area
was relatively constant. Thiol-functionalized silica spheres with 40% thiol loading resulted
in microporous materials with hydrophobic pore surfaces for water vapor adsorption.
The effect of macropore formation in catalyst supports on the oxidation activity for diesel fuel mist was examined with the goal of improving catalyst efficiency. To investigate the effect on a laboratory scale using granular samples, we designed a reaction system that supplied fuel mist to the catalyst bed directly by an air atomizing nozzle. The catalytic activity was found to be improved by macropore formation in the support. This effect was also demonstrated for a washcoated catalyst on a honeycomb with diesel engine exhaust. These results suggest that the macropore diffusion channels are secure even if fuel mist attaches to the support surface, and the reactant gas can diffuse to the interior of the support and reach the active sites. Macropore formation prevented the blockage of pores of the support surface and thus the active sites of the catalyst.
Both the extent of SiO2 doping and the mesopore size
of alumina were investigated with the aim of developing a support
that maintains high activity during the catalytic oxidation of diesel
exhaust hydrocarbons and NO over 0.75 wt % Pt/0.25 wt % Pd even after
high temperature treatment. By controlling the SiO2 doping
ratio and heat treatment conditions during the preparation process,
24 types of SiO2–Al2O3 were
obtained, with SiO2 levels from 0 to 5.9 wt % and mesopore
sizes from 6.7 to 10.2 nm. The highest catalytic activity was obtained
at a SiO2 loading of approximately 4 wt %, and the beneficial
effects of SiO2 doping were thought to result from optimization
of the basicity of the support. Catalytic activity improved as the
mesopore size increased up to approximately 10 nm. Computational simulations
confirmed that the diffusion limitations of small mesopore structures
may affect catalytic activity when the mesopores are below 10 nm.
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