Oxidation of trace ethylene (50 ppm) at 0 °C was systematically studied using Pt nanoparticles supported on mesoporous silica (SBA-15) in a fixed-bed flow reactor. The SBA-15 supported Pt catalyst (1.8 wt % Pt loading) exhibited an ethylene conversion higher than 99% at the initial stage, which gradually began to decrease at 90 min and reached 33% within 240 min. The CO2 yield was lower than the corresponding ethylene conversion before the steady state was reached. This was due to the formation of intermediates that were stabilized on the catalyst surface. These intermediates could be recovered in the form of CO2 by heating the spent catalyst in a mixed N2 and He (1:19, v/v) flow at 150 °C. The addition of water vapor to the catalyst bed decreased the original activity drastically because physically adsorbed water molecules partly blocked the active Pt sites. Control experiments using nonordered silica supports (Aerosil 380 and 200) showed similar catalytic behavior as that observed with SBA-15. The formation of highly dispersed Pt nanoparticles on the silica surfaces is thus the key to the development of effective Pt catalysts for low-temperature oxidation of ethylene.

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Structure-activity relationship of silica-supported Pt catalysts in aerobic oxidation of 50 ppm ethylene was studied at 0 °C with a fixed-bed flow reactor and in-situ characterization techniques using FTIR (Fourier-transform infrared) spectroscopy. The activity of all Pt catalysts examined here decreased by water molecules formed during stoichiometric oxidation of ethylene and became stable steadily. Mesoporous silica-supported Pt catalyst improved its steady-state activity after calcination of the support in air at 800 °C, whereas no such effect was observed for nonporous silica support. CO-pulse titration, H2O adsorption measurements, 29 Si MAS NMR, and in-situ FTIR along with catalytic activity studies revealed that the activity of mesoporous silica-supported Pt catalyst is higher than that of nonporous silica-supported ones, despite similar hydrophobicity and low Pt dispersion. In-situ characterization using CO as a molecular probe indicates that a part of Pt surface inside hydrophobic mesopores is not involved in hydrogen-bonding network among physisorbed water molecules and surface SiOH groups even after full hydration of catalyst surface, and bare Pt sites are expected to work more effectively for ethylene oxidation. Such "hydrophobic Pt surface" can only be formed on hydrophobic mesoporous silica support, which is probably due to Pt nanoparticles surrounded with hydrophobic siloxane network entirely. Unique environment derived from condensed siloxane network and restricted mesopores contributes largely to high activity of Pt nanoparticles for low temperature oxidation of trace ethylene.

Water-in-oil microemulsions have been found to be good templates for synthesis of ZnO and ZnO@Ag nanoparticles and offered themselves as ideal ‘nanoreactors’ for uniform fabrication of core@shell nanoparticles.

A distinctive synthetic method for the efficient synthesis of multifunctional bimetallic plasmonic Au@Ag core@shell nanoparticles (NPs) with tunable size, morphology, and localized surface plasmon resonance (LSPR) using Triton X-100/hexanol-1/deionized water/cyclohexane-based water-in-oil (W/O) microemulsion (ME) is described. The W/O ME acted as a “true nanoreactor” for the synthesis of Au@Ag core@shell NPs by providing a confined and controlled environment and suppressing the nucleation, growth, agglomeration, and aggregation of the NPs. High-resolution transmission electron microscopic analysis of the synthesized Au@Ag core@shell NPs revealed an “unusual core@shell” contrast, and the selected area electron diffraction and Moiré patterns showed that Au layers are paralleled to Ag layers, thus indicating the formation of Au@Ag core@shell NPs. Interestingly, the UV–visible spectrum of the Au@Ag core@shell NPs exhibited enthralling plasmonic properties by introducing a high-frequency quadrupolar LSPR mode originated from the isolated Au@Ag NPs along with a low-frequency dipolar LSPR mode originated from the coupled Au@Ag NPs. The effective plasmonic enhancement of the Au@Ag core@shell NPs is attributed to the extreme enhancement of the localized electromagnetic field by coupling of the localized surface plasmons of the Au core and Ag shell. The mechanisms for the nucleation and growth of Au@Ag core@shell NPs in W/O ME have been proposed. A unique electron transfer phenomenon between the Au core and Ag shell is elucidated for better understanding and manipulation of the electronic properties, which evinced the development of Au@Ag core@shell NPs through suppression of the galvanic replacement reaction.