Title : A novel, low cost material for automotive catalysis
Abstract:
Catalytic processing of vehicle exhaust emissions to reduce their impacts on air quality currently requires large quantities of expensive Platinum Group Metals (PGMs). Whilst technologies for oxidation of CO are relatively mature, new materials capable of catalysing the reduction of NOx are needed in order to meet emissions targets. Here we present a novel, low cost material (LowCat) capable of catalysing CO oxidation and NOx reduction simultaneously. The mechanism of action of the catalyst is investigated both computationally and experimentally to inform its real world use. The LowCat material binds O2, which can then oxidise two equivalents of CO, NO can also be oxidised by this surface O2, a temperature dependent process observed here above 175°C, yielding NO2 in the gas phase and an isolated O bound to the surface. NH3 can bind to a neighbouring site, yielding NH2 and OH radicals on the surface. NO can react with the NH2 to give N2 and H2O, whilst a further NH3 inserts into the bond between the OH and the surface. Reaction of a further NO, either with this bound complex or an NH2 radical after emission of H2O, produces further H2O and N2. The lone surface bound O, which is crucial to the further sequence of reactions leading to NO reduction, is also readily produced from surface reduction of NO2 to NO. This route for producing surface O from NO2 is active and allows reduction of NOx even at room temperature. This mechanism is in agreement with previous results on similar catalyst surfaces, but with catalytic rates sufficient to produce reduction of NOx in real world engines. Such an efficient, affordable catalyst capable of simultaneously oxidising CO and reducing NOx even from cold start engines could have significant impacts on human health.
