Reduction of NOx over Fe/ZSM-5 catalysts: mechanistic causes of activity differences between alkanes

Fe/ZSM-5 catalysts prepared by sublimation of FeCl₃ onto H/ZSM-5 catalyze the selective reduction of NO_x by hydrocarbons to N₂. The order of the relative rates and N₂ yields obtained with different alkanes reveals a non-trivial chemistry. The maximum yield is lower for propane than for n-butane but about the same for n- and iso-butane. However, at temperatures below this maximum, the N₂ yield is higher for propane and n-butane than for iso-butane. Deposits are formed on the catalyst that contain N atoms in a low-oxidation state which are able to react with NO₂ to form N₂. TPO and FTIR results show that the amount and also the character of the deposits depend on the nature of alkanes. The change of the oxidation state of nitrogen from a high value in NO or NO₂ to a lower value in nitrile and amino groups of the deposit is rationalized by applying mechanistic concepts of organic chemistry, including the Beckmann rearrangement and fragmentation. FTIR spectra and the observed oxygen- and nitrogen-containing compounds by GC-MS are potential clues to the reaction mechanism.     

Azide: A Unique Dipole for Metal‐Free Bioorthogonal Ligations

Covalently bound azide on a (small) organic molecule or a (large) biomolecular structure has proven an important handle for bioconjugation. Azides are readily introduced, small, and stable, yet undergo smooth ligation with a range of reactive probes under mild conditions. In particular, the potential of azides to undergo metal‐free reactions with strained unsaturated systems has inspired the development of an increasing number of reactive probes, which are comprehensively summarized here. For each individual probe, the synthetic preparation is described, together with reaction kinetics and the full range of applications, from materials science to glycoprofiling. Finally, a qualitative and quantitative comparison of azido‐reactive probes is provided.     

Dynamical behavior of copper atoms in a carbon nanotube channel

The transportation of copper atoms along a carbon nanotube (CNT) channel, which consists of a junction, is studied using molecular dynamics simulations. A bias voltage is applied along the channel to induce an electromigration force on copper atoms. The study focuses on the flow of copper atoms by varying the voltage gradient and the temperature of copper. The results show that the temperature increase due to electromigration forces is lower when the initial temperature of copper is higher. A higher temperature results in larger thermal vibrations of copper atoms, which partly contributes to a change in the atomic arrangement of copper when copper is transported along the channel. This change occurs due to the existence of the CNT channel junction. Besides this, the interactive forces between copper and the CNT channel are significant when copper is approaching the junction. The effect of temperature on the interactive forces at the junction of the channel is more prominent than the effect of electromigration forces. The resistive forces on copper produced by the CNT channel are quite insignificant for a straight channel, but are more prominent when copper is flowing against the obstruction of the CNT channel junction.     

Electrochemical doping of graphene with toluene

The electrical properties of graphene are known to be modified by chemical species that interact with it. We investigate the effect of doping of graphene-based devices by toluene (C₆H₅CH₃). We show that this effect has a complicated character. Toluene is seen to act as a donor, transferring electrons to the graphene. However, the degree of doping is seen to depend on the magnitude and polarity of an electric field applied between the graphene and a nearby electrode. This can be understood in terms of an electrochemical reaction mediated by the graphene crystal.     

Sustainable energy development: performance and prospects

Concerns about sustainability, and the harsh realities of environmental catastrophe, can be traced back at least 4000 years. This paper points out how human pressures on the surrounding environment have had severe consequences over this period, coal burning has had adverse consequences traceable over the past 750 years, and the adverse environmental impacts of using other fossil fuels have aroused attention more recently. Heightened awareness of the need for sustainable development is a modern development, evident in international and national debates since the early 1970s. With the Brundtland Commission report published in 1987 came a framework for sustainable energy development. However, performance under the four elements of that framework have been almost uniformly disappointing. Fossil fuel use has continued to rise; renewable energy use has made insufficient inroads; waste and inefficiency in energy usage continues to be far too high; too many people remain without modern energy services or are exposed to severe pollution in the home and local atmosphere; there are mounting concerns about the conventional oil resource base—and future supplies and prices of oil and natural gas; greenhouse gas emissions continue to rise and evidence of human-induced climate change continues to mount. Indices of national environmental performance suggest no country is performing adequately; population, housing and transportation pressures result in greater pollution, loss of natural habitats, and species reduction; and poor governance is frequently cited as a major cause of poor environmental performance. The prospects for sustainable energy are bleak on current trends.