Reactors that burn hydrogen or natural gas to generate energy can be dirty and dangerous.
The mix of air with hydrogen or natural gas can explode easily if composition and temperature are not carefully controlled. And reactors often produce polluting by-products.
NowUniversity of Pittsburgh chemical engineering professor Goetz Veser has created a safer alternative – microreactors that will not explodeno matter what the gas composition or how hot they getand that can keep undesirable pollutants such as nitrogen oxides (NOx)from forming. His results could be used to design processes for safeclean energy production and hydrogen storage.
Reactor explosions
Reactor explosions can happen either when the reaction gets too hot or when atoms called free radicals break away and start to split the bonds of other molecules. In both casesthe reaction speeds up and the temperature increases until there is an explosion.
But Veser’s microreactors are actually inherently safehe says. “Even if the temperature goes completely through the roofbased on the kinetics of the systemexplosions cannot happen.”
Veserwho also is a researcher in Pitt’s Gertrude E and John M Petersen Institute of NanoScience and Engineeringcreated the reactors by etching tiny channels into silicon chipsusing a platinum wire catalyst and running a mix of hydrogen and air through the channel (Fig.1).
“It’s one of the toughest systems you can imagine” he says. “If anything would blow upthis would.”
But nothing happened – other than the controlled burning of hydrogen. The walls did indeed adsorb any radicals floating aroundkeeping the reaction running smoothly.
Veser has since extended the technology to burning methane and has found that not only can the walls stave off explosionsthey also can steer the course of the reaction. For examplesome NOx is formed by the heat and some by radicals. Veser found that at a particular sizethe microreactor walls adsorb the radicals that cause NOxwhile letting the reaction go ahead.
“This is a completely different way of approaching a clean combustion technology” he concluded.
Nano cages
Lock one or more molecules up within a cage of nanometer dimensions. Take this ‘nanocontainer’ to the desired spot and free the molecules. Or keep them locked up for a while and introduce other molecules into the containerfor chemical reactions to occur inside. By using polymers containing ironit is possible to make intelligent containers of which the access of molecules can be regulated in a chemical way.
A research team led by prof Julius Vancso of the MESA+ Institute for Nanotechnology at the University of Twente in the Netherlands has succeeded in fabricating these nanocontainers. The scientists foresee many exciting applicationsincluding ultrafast reactions in nano chemistry.
A true breakthrough in this research is the use of polymers having iron in their main chain. This is the material the containers are made of.
By using ironfor the first time it is possible to adjust the permeability of the material via oxidation and reduction reactions.
Scientists Yujie Ma and Mark Hempeniusboth with Vancso’s groupsucceeded in creating containers that can be opened and closed in this ‘chemical’ way. Oxidants or reductants take care of the access: an oxidant can be iron chloridefor example. A reductant could even be vitamin C.
This selective access – one molecule gets inthe other will not – is the result of the layered structure of the wall of the container. Polymer chains are layererd on top of each other and an electrostatic charge keeps them together. Influencing this charge with redox reactions immediately influences the permeability of the wall.
As oxidation and reduction steps take part in numerous biochemical processes in waterthe nanocontainers are useful for a variety of biological and biomedical applications. The scientists foresee applications in green areas such as food additivesmedicine and cosmetics. In a more fundamental waynanocontainers could be used in biochemistry to study large numbers of enzyme reactions at the same time and with high throughput.
The researchled by Vancsohas been carried out in close cooperation with the group of professor. Helmuth Möhwald of the Max Planck Institut für Kolloid- und Grenzflachenforschung in Golm.
The article Redox-controlled molecular permeability of composite-wall microcapsules is published in the latest issue of Nature Materialswww.nature.com/nmat
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