Oxidation of n-hexadecane with uranyl loaded/anchored microporous zeolites and ozone

Revelation of contributing mechanism of reactive oxygen species in photocatalytic ozonation heterocyclization of gaseous hexane isomers

The reactive oxygen species (ROS) involved photocatalytic ozonation of gaseous n-hexane to heterocyclic compounds has been recently reported. However, whether such heterocyclization reaction happens on other alkanes and what is the contributing mechanism of ROS to the heterocyclic compound formation are still unclear. In present study, photocatalytic ozonation of three n-hexane's isomers (i.e. 2-methypentane, 3-methylpentane and 2,3-dimethylbutane) on Cu₂O-CuO/TiO₂-foam ceramic was investigated. Within reaction period, 2-methylpentane and 3-methylpentane not only showed higher average degradation efficiency than 2,3-dimethylbutane, but also separately converted to interfacial heterocyclic compounds of 5,5-dimethyldihydro-2(3H)-furanone and 4,5-dimethyl-4,5-dihydro-2(3H)-furanone. Enough reaction time, optimum experimental atmosphere and shorter light wavelength benefited the formation of heterocyclization products. None of O₃, ¹O₂, electron and hole directly contributed to the heterocyclic compound formation. While ^•O₂^- dominated the production of the heterocyclic compound under the dry reaction atmosphere and ^•OH showed more important role than ^•O₂^- in the heterocyclic compound formation under the moist reaction atmosphere. Theoretical calculation confirmed that ^•OH or ^•O₂^- induced heterocyclization reaction of alkane was exothermic, while the former reaction released 0.47 eV higher energy than the later reaction. The findings provide a comprehensive understanding of contributing roles of ROS in heterocyclization reaction of alkanes, and are helpful for effective elimination of industrial alkanes by advanced oxidation methods.

Lubricant degradation and related wear of a steel pin in lubricated sliding against a steel disc

In lubricated sliding contacts, components wear out and the lubricating oil ages with time. The present work explores the interactive influence between lubricant aging and component wear. The flat face of a steel pin is slid against a rotating steel disk under near isothermal conditions while the contact is immersed in a reservoir of lubricant (hexadecane). The chemical changes in the oil with time are measured by vibrational spectroscopy and gas chromatography. The corresponding chemistry of the pin surface is recorded using X-ray photoelectron spectroscopy while the morphology of the worn pins; surface and subsurface, are observed using a combination of focused ion beam milling and scanning electron microscopy. When compared to thermal auto-oxidation of the lubricant alone, steel on steel friction and wear are found to accentuate the decomposition of oil and to reduce the beneficial impact of antioxidants. The catalytic action of nascent iron, an outcome of pin wear and disk wear, is shown to contribute to this detrimental effect. Over long periods of sliding, the decomposition products of lubricant aging on their own, as well as in conjunction with their products of reaction with iron, generate a thick tribofilm that is highly protective in terms of friction and wear.