Santosh K.C.,University of Texas at Dallas |
Wang W.,University of Texas at Dallas |
Wang W.,Nanostellar |
Dong H.,University of Texas at Dallas |
And 4 more authors.
Journal of Applied Physics | Year: 2013
A theoretical study of the oxidation of InP(001)-(2 × 4) surface is performed using density functional theory methods. Our results on surface oxidation show that the oxygen adsorption does not produce any gap states in the bulk InP band gap, due to the saturation of surface In dangling bonds, whereas substitutional oxygen atoms produce gap states. This study also shows that the surface stability increases with the oxygen content, indicating a strong tendency for surface oxidation. Our results help to clarify the origin of surface gap states upon surface oxidation and provide an insight at the atomic level the mechanism of surface oxidation, which will assist in the understanding of the degradation of III-V devices upon oxygen exposure or interfacial oxidation with high dielectric constant oxides. © 2013 American Institute of Physics. Source
Nanostellar | Date: 2010-12-30
An emission control catalyst is doped with bismuth, manganese, or bismuth and manganese. The doped catalyst may be a palladium-gold catalyst or a platinum-based catalyst, or both. The doped palladium-gold catalyst and the doped platinum-based catalyst may be contained in a single washcoat layer or in different washcoat layers of a multi-brick, multi-zoned, or multi-layered emission control system. In all embodiments, zeolite may be added as a hydrocarbon absorbing component.
Nanostellar | Date: 2013-04-01
A monomer is added to a solvent containing metal salt and porous support materials and the solvent is stirred for a period of time to distribute and fix the metal in the pores of the support materials. The solids that are dispersed in the solvent are then separated from the liquid, dried and calcined to form heterogeneous catalysts. The monomer that is added is of a type that can be polymerized in the solvent to form oligomers or polymers, or both. When forming heterogeneous catalysts containing platinum, acrylic acid is selected as the preferred monomer.
News Article | October 20, 2006
Guess how much platinum there is in a Volkswagen Passat diesel? If you said $238 worth, you'd be right. Nanostellar is trying to reduce it. The company, which focuses on car emissions, has produced a platinum alloy that can substitute for the pure material inside catalytic converters, according to CEO Pankaj Dhingra. Recently, it began production of 250 kilograms a week. Platinum sprinkled in the catalytic converter captures gases like carbon monoxide and turns them into less dangerous compounds, such as carbon dioxide. But platinum costs a lot. Nanostellar's particles can cut around $56 to $117 out of the platinum budget and cut down on emissions. Crooks have also been stealing catalytic converters for the platinum lately. The stuff sells for $1,100 an ounce, after all. Nanostellar is trying to land deals with automakers, but its materials will end up in aftermarket converters in the relatively near future.
News Article | August 20, 2012
Modern diesel engines are more fuel efficient than gasoline engines. Cleaning up their exhaust is a bit more challenging, though, due to the large amount of oxygen involved in the combustion. In particular, removing the nitrogen oxides (NO ) formed as oxygen and nitrogen in the air reacting at high temperatures requires specialized systems and expensive catalysts like platinum. While everyone would like to get rid of the platinum, no materials have been found that match its catalytic performance in diesel engine exhaust. Until now, apparently. Research published recently in Science describes a new catalyst, a complex mixture of metal oxides including manganese, mullite, and the rare earth metals samarium and gadolinium (Mn-mullite (Sm, Gd)Mn O , to be precise), that actually performs better than platinum. And it’s cheaper. The work was performed by scientists at the nanotechnology startup Nanostellar, with collaborators at the Huazhong University of Science and Technology, University of Kentucky, and the University of Texas at Dallas. Let’s take a step back: why do we need these catalysts in the first place? At the high temperatures inside engines (around 1900K), oxygen and nitrogen in the air begin to dissociate and react to form nitric oxide (NO). Nitrogen dioxide (NO ) can then form by the oxidation of NO, but this is much slower—meaning most of the NO in the exhaust is just NO. There are two common ways to remove NO from diesel exhaust. The first is selective catalytic reduction (SCR), which reacts NO and NO with ammonia or urea in the presence of a (non-platinum) catalyst, forming nitrogen and water. The second is the NO trap, where zeolites absorb the molecules like a sponge. Later, the stored molecules can be reacted with excess fuel to release nitrogen. In both cases, you want to convert some of the NO into NO (the SCR reaction is fastest when you have equal amounts of the two, and the NO trap stores NO more efficiently). This is where the platinum comes into the picture: a catalyst is needed to jumpstart the reaction between oxygen and NO to form NO . Back to the new catalyst: how did it perform? The researchers exposed the material to a gas mixture of 450 parts per million NO and 10 percent oxygen (the rest was inert helium). Over a range of temperatures, the new catalyst performed better than platinum (around 64 percent better at 300 degrees C, and 45 percent better at 120 degrees C). Diesel engines also contain catalytic converters to remove carbon monoxide and unburned hydrocarbons. The authors added their new material to a commercial catalyst (based on platinum and palladium), and found that it oxidized NO without impeding the catalyst's original function. The next step, then, would be to create a catalyst (or modify this new one) that could replace the entire system—removing platinum altogether.