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Recent interest in the use of nanoparticles in emulsion stabilization has driven increased efforts to understand how the characteristics of the particles influence the emulsion properties. While it is clear that the contact angle and wettability must play significant roles in determining the type of emulsion formed, it is not straightforward to measure the contact angle of a nanoparticle. In this paper, we compare multiple techniques for characterizing the water-air contact angle of silica nanoparticles while systematically varying the hydrophobicity of the nanoparticles using silanization. We then compare the performance of the particles in decane/water emulsions. While the heat of immersion measured by microcalorimetry is found to provide the best method for discriminating between the wettability of the particles, the fraction of surface covered by the silane groups was observed to affect the structure of the emulsion more profoundly than the differences in the contact angles of the particles. Furthermore, we find that the phase of initial dispersion is extremely influential in determining the resulting emulsion type and droplet size [ABSTRACT FROM AUTHOR]

Soot particulate collected from a Euro III heavy duty diesel engine run under black smoke conditions was investigated using thermogravimetry, transmission electron microscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy. The characterization results are compared with those of commercial carbon black. The onset temperature toward oxidation of the diesel engine soot in 5% O2 is 150 °C lower than that for carbon black. The burn out temperature for the diesel engine soot is 60 °C lower than that of the carbon black. The soot primary particles exhibit a core-shell structure. The shell of the soot particles consists of homogeneously stacked basic structure units. The commercial carbon lamp black is more graphitized than the diesel engine soot, whereas the diesel engine soot contains more carbon in aromatic nature than the carbon black and is highly surface-functionalized. Our findings reveal that technical carbon black is not a suitable model for the chemistry of the diesel engine soot. [ABSTRACT FROM AUTHOR]

Reduction of MoO3 in propene and oxidation of MoO2 in oxygen are investigated by in situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Temperature-programmed and isothermal experiments (573–773 K) are performed to elucidate the structural evolution of phases present during the reactions and, in addition, to reveal the solid-state kinetics of the processes involved. During the reduction of MoO3 in propene and the oxidation of MoO2, only crystalline MoO3 and MoO2 were detected by in situ XRD. The formation of a “Mo18O52”-type shear structure as intermediate during reduction of MoO3 in propene and during oxidation of MoO2 in oxygen was observed by in situ XAS. The solid-state kinetics of the reduction of MoO3 in propene exhibits a change in the rate-limiting step as a function of both temperature and extent of reduction. The solid-state kinetics of the oxidation of MoO2 is governed by three-dimensional diffusion. A schematic reaction mechanism for the reduction of MoO3 in propene and reoxidation in oxygen is proposed that consists of (i) generation of oxygen vacancies at the (100) or (001) facets by reaction with propene, (ii) vacancy diffusion in the MoO3 bulk, (iii) formation of Mo18O52-type shear structures in the lattice, and (iv) formation and growth of MoO2 nuclei. With respect to a redox mechanism for the partial oxidation of propene on MoO3, three stages are distinguished. (i) at temperatures below ∼600 K the participation of oxygen from the MoO3 bulk is negligible. (ii) At temperatures between ∼600 and ∼700 K oxygen vacancy diffusion in the bulk is sufficient to make a redox mechanism feasible, affording a partially reduced MoO3 under reaction conditions. (iii) At temperatures above ∼700 K sufficiently fast oxygen diffusion in the lattice combined with rapid formation and annihilation of crystallographic-shear planes permits the participation of a considerable amount of the lattice oxygen of MoO3 in the partial oxidation of propene. [Copyright &y& Elsevier]