Surfactants exhibit maxima in their critical micelle concentrations upon application of hydrostatic pressure, which is attributable to changes in their volumes of micellization from positive to negative values with increasing pressure. We present a direct molecular simulation analysis of the volumes of micellization of an anionic, cationic, and nonionic surfactant in aqueous solution at pressures up to 2500 bar. Excellent agreement with experiment is observed. A Kirkwood-Buff theory analysis based on proximal solvent distributions permits the breakdown of the volumes of micellization into constituent surfactant headgroup and tailgroup contributions. Although the micellization volume crossover is analogous to the transfer of an alkane from water to its pure liquid, significant differences are observed, including lower compressibilities of micelle volumes compared to that of the alkane liquid, negative partial compressibilites for anionic sulfated surfactant monomers, and large nonionic ethoxy headgroup contributions to the micellization volume.
Fischer–Tropsch synthesis is an attractive process to convert alternative carbon sources, such as biomass, natural gas, or coal, to fuels and chemicals. Deactivation of the catalyst is obviously undesirable, and for a commercial plant it is of high importance to keep the catalyst active as long as possible during operating conditions. In this study, the reactivity of CO on carbon-covered cobalt surfaces has been investigated by means of density functional theory (DFT). An attempt is made to provide insight into the role of carbon deposition on the deactivation of two cobalt surfaces: the closed-packed Co(0001) surface and the corrugated Co(112̅1) surface. We also analyzed the adsorption and diffusion of carbon atoms on both surfaces and compared the mobility. Finally, the results for Co(0001) and Co(112̅1) are compared, and the influence of the surface topology is assessed.
Nitrogen oxides, NOx, are formed in combustion engines. They contribute to acid rain and the formation of ozone and are hazardous for men and environment. In this article, a process was investigated that can 'capture' the NOx from the exhaust gases using heteropoly acids and can later release them for processing. One of the main conclusions is that the mobility of the captured and released molecules is the key to control the reaction. This can now be used to optimize and commercialize the technology.
Stikstofoxiden, aangeduid als NOx, worden gevormd in verbrandingsmotoren. Ze dragen bij tot zure regen, de vorming van ozon en zijn dus schadelijk voor mens en milieu. In dit artikel werd een proces onderzocht dat de NOx kan ‘vangen’ uit de uitlaatgassen aan de hand van heteropolyzuren en later terug kan vrijgeven voor verdere verwerking. Een van de belangrijkste vaststellingen is dat de mobiliteit van de opgeslagen en vrijgegeven moleculen de sleutel is voor het controleren van het proces. De conclusies van het onderzoek kunnen nu verder gebruikt worden voor de optimalisering en commercialisering van het proces.
NOx adsorption on Phosphotungstic acid is entropy-driven due to the watermolecules that are released.