News Catalysis Diesel zeolite destroys NO Anthony King
The newest catalytic converters for diesel engines rely on a synthetic version of the natural zeolite mineral chabasite called Cu-SZZ-13, which converts the nitric oxide (NO) in engine exhausts to harmless nitrogen and water when ammonia is added. But how it works was not entirely clear.
Now scientists in the US and South
Korea report that the artificial catalyst works in much the same way that bacterial enzymes do – by coming at the target NO side-on rather than headfirst (Angew. Chem. Int. Ed., doi: 10.1002/anie.201303498). Cu-SZZ-13 is a crystalline aluminosilicate mineral that accommodates a copper ion in its well- defined pore structures. The scientists found that the copper hooks up with NO directly and borrows one of its electrons, resulting in a charged NO that reacts with ammonia in the first of several chemical
Flexible electronics Twisting the light away Kathryn Roberts
Flexible electronics – which bend and stretch without losing any of their properties – are hailed as the key to next generation display technology. From fashionable smart clothing and phones that can be squashed into your pocket, through curtains that light up a room, to in vivo or epidermal medical devices, the applications promise to brighten up our lives. The holy grail of such devices remains the fabrication of stretchable thin-film transistors. Now, researchers at the University of California, Los Angeles (UCLA), US, have reported a significant building block towards their development by making a transparent elastomeric polymer light-emitting device (EPLED) that can be repeatedly stretched, folded and twisted at room temperature while remaining lit and retaining its original shape. The EPLED comprises an electroluminescent layer sandwiched between a pair of transparent elastomeric composite electrodes. The electrodes
18 Chemistry&Industry • November 2013
conductor polyethylene oxide (PEO) and lithium trifluoromethane (LiTf). According to the researchers, the EPLED is
semi-transparent and emits from both surfaces with a high light-emitting efficiency. They were able to stretch and re-stretch the EPLED 1000 times, extending it 30% beyond its original shape and it still continued to work at high efficiency; it could be stretched twice its original size and twisted and folded in multiple directions while still functioning. In a proof-of-concept experiment, the researchers made a fully stretchable EPLED array of 5 x 5 pixels to demonstrate the potential of the EPLED architecture for stretchable OLED displays. Poopathy Kathirgamanathan, professor of
are made up of a thin silver nanowire network inlaid in the surface of a poly(urethane acrylate) matrix (Nature Photonics, doi:10.1038/ nphoton.2013.242). The electroluminescent layer is a blend of a high molecular yellow light emitting polymer, which is highly stretchable , the ionic
organic electronics at Brunel University, UK, comments: ‘This stretchable OLED is an exciting step forward to flexible display technology. But, the light emitting electrochemical cells employed here require high voltage and usually have very short life-times. The lifetime is the key, so these are unlikely put the curved OLED-TV out of business for quite some time.’
steps, ultimately generating atmospheric nitrogen and water. ‘The main finding is the identification of a side-on nitrosyl species that we suggest to be the key intermediate in the NH3
[reaction],’ explains Janos Szanyi, senior author at the Pacific Northwest National Laboratory in Richland, Washington. The NO+
spectroscopy studies and its structure determined using NMR spectroscopy. ‘The surprising thing about this
finding was that it had been identified as a key intermediate in nitrite reductase enzymes which also have Cu ions as active catalytic centres. That pointed us to a commonality of zeolite and enzyme catalysis: nature can teach us how to design catalysts to specific applications, we just need to list to it,’ says Szanyi. Nitrite reductase breaks down nitrites into atmospheric nitrogen. The mechanism also explains why
nitrous oxide, a greenhouse gas produced was found in FTIR
by other zeolite catalysts, is not generated by Cu- SZZ-13.
Russell Morris of the University of St Andrews in the UK, an expert in zeolite catalysts, describes the insights as exciting and says they could lead to improved catalytic converters. He says this particular zeolite is ‘a hot material right now’ because of its ‘impressive stability’ in these NOx reactions. ‘If you understand the mechanism of what is happening [with SSZ-13] then you can design better ones. Since the zeolite is similar to the enzymes, we can now look at all the work done on the enzymes and see if that can help us design a new zeolite.’ The research was funded by the US Department of Energy.
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