Significance Electronic cigarettes, also known as e-cigarettes, are devices designed to imitate regular cigarettes and deliver nicotine via inhalation without combusting tobacco. They are purported to deliver nicotine without other toxicants and to be a safer alternative to regular cigarettes. However, little toxicity testing has been performed to evaluate the chemical nature of vapour generated from e–cigarettes. The aim of this study was to screen e-cigarette vapours for content of four groups of potentially toxic and carcinogenic compounds: carbonyls, volatile organic compounds, nitrosamines and heavy metals. Materials and methods Vapours were generated from 12 brands of e-cigarettes and the reference product, the medicinal nicotine inhaler, in controlled conditions using a modified smoking machine. The selected toxic compounds were extracted from vapours into a solid or liquid phase and analysed with chromatographic and spectroscopy methods. Results We found that the e-cigarette vapours contained some toxic substances. The levels of the toxicants were 9–450 times lower than in cigarette smoke and were, in many cases, comparable with trace amounts found in the reference product. Conclusions Our findings are consistent with the idea that substituting tobacco cigarettes with e-cigarettes may substantially reduce exposure to selected tobacco-specific toxicants. E-cigarettes as a harm reduction strategy among smokers unwilling to quit, warrants further study. (To view this abstract in Polish and German, please see the supplementary files online.)

Ammonia emission to the atmosphere is an important environmental problem. A significant increase in ammonia emission is expected in automotive and energy production sectors in the near future. It is related to the spreading of technologies that use ammonia for NO_x conversion in flue gases (e.g. DeNOx, DEF) and combustion of nitrogen rich fuels (e.g. biogas, biomass). Among the various methods of ammonia elimination from flue gases, its catalytic selective oxidation to dinitrogen seems to be the most promising one. Different types of catalytic systems active in selective ammonia oxidation are presented and discussed. Moreover, the possible mechanisms of ammonia oxidation and the concept of a bifunctional catalyst are discussed and analysed. Finally, future trends in these studies are suggested.

Rigorous regulations of nitrogen oxide emissions require the development of technologies for their removal from exhaust gases. Implementation of appropriate catalysts can potentially promote NO_x (NO, NO₂) or N₂O removal in shorter reaction time and under milder operation conditions. However, several challenges have to be faced upon trying to address nitrogen oxide pollution with catalytic systems such as sufficient catalytic performance, suitable operational temperatures and catalyst poisoning. The flexible structure of hydrotalcite-like compounds offers the opportunity to introduce various metals into the materials to provide active and selective catalysts for NO_x and N₂O removal. This minireview summarizes the abatement of nitrogen oxides by using hydrotalcite-derived mixed metal oxides. At first, a brief overview on the general features of hydrotalcite-originated mixed metal oxides and their applications in catalysis is provided. Later on, the application of mixed metal oxides as SCR catalysts with both ammonia (NH₃-SCR) and hydrocarbons (HC-SCR) as reducing agents is discussed. An overview of the mixed metal oxides applied as catalysts for NO_x storage/reduction (NSR) and further in the simultaneous removal of NO_x and soot particles is provided. Additionally, this review discusses mixed metal oxides as efficient catalysts for catalytic decomposition (deN₂O) and selective catalytic reduction of N₂O (N₂O-SCR). Finally, the remaining challenges and future trends are highlighted.