When methane was passed over MgO at temperatures of approximately 500 O C , methyl radicals were produced on the surface, released into the gas phase, and trapped downstream in a solid argon matrix where they were analyzed by EPR spectroscopy. Significant differences in initial activity were observed, depending on whether the MgO was pretreated under vacuum or a flow of oxygen. Vacuum conditioning led to essentially no activity while oxygen conditioning resulted in substantial radical production. The oxidant of choice was also critical. Nitrous oxide resulted in a continuous decline of activity while in the presence of oxygen the formation of radicals was at a steady state. Doping of MgO with lithium, sodium, or iron was also examined. Lithium was found to greatly increase the activity up to a doping level of approximately 15.0 wt %. Two pathways are believed to be responsible for the radical formation. Over pure MgO, intrinsic cation vacancies react with molecular oxygen to give an 0-center which can abstract a hydrogen atom from methane to produce the methyl radical. For the lithium-doped samples, substitutional Li' ions react with molecular oxygen to form a [Li'O-] center which is also capable of abstracting a hydrogen atom from methane.
Currently, a novel coronavirus named “SARS-CoV-2” is spreading rapidly across the world, causing a public health crisis, economic losses, and panic. Fecal–oral transmission is a common transmission route for many viruses, including SARS-CoV-2. Blocking the path of fecal–oral transmission, which occurs commonly in toilet usage, is of fundamental importance in suppressing the spread of viruses. However, to date, efforts at improving sanitary safety in toilet use have been insufficient. It is clear from daily experience that flushing a toilet generates strong turbulence within the bowl. Will this flushing-induced turbulent flow expel aerosol particles containing viruses out of the bowl? This paper adopts computational fluid dynamics to explore and visualize the characteristics of fluid flow during toilet flushing and the influence of flushing on the spread of virus aerosol particles. The volume-of-fluid (VOF) model is used to simulate two common flushing processes (single-inlet flushing and annular flushing), and the VOF–discrete phase model (DPM) method is used to model the trajectories of aerosol particles during flushing. The simulation results are alarming in that massive upward transport of virus particles is observed, with 40%–60% of particles reaching above the toilet seat, leading to large-scale virus spread. Suggestions concerning safer toilet use and recommendations for a better toilet design are also provided.
A previous study of Li-promoted MgO catalysts, which are effective in the partial oxidation of methane, led to the conclusion that [Li+0~] centers are important in the formation of CH3* radicals. Because of their role in this catalytic process, the formation and thermal stability of these centers have been studied in more detail. The [Li+0"] centers are present in the Li/MgO powders at temperatures as low as 673 K. They have a positive heat of formation (AH = 3 kcal mol"1); thus, the concentration of the centers increases with increasing temperatures. Upon quenching the powder in liquid 02 to 77 K, the [Li+0"] centers are frozen in and can be detected by EPR spectroscopy. In addition to the [Li+0~] centers, the paramagnetic 02~a nd 03" ions also are present. The latter species is formed by the reaction of O" with 02 in the solid or on the surface, depending upon the treatment of the samples. The [Li+0"] centers also may be formed by irradiation of the Li/MgO powders at 77 K with 254-nm light. Both methods of preparation (quenching and irradiation) result in [Li+0"] centers which are
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