OpeSpeKin · Combined operando spectroscopy with model-based experimental design to study the mechanism of catalytic surface reactions

Combined operando spectroscopy with model-based experimental design to study the mechanism of catalytic surface reactions

Selective catalytic reduction (SCR), also referred to as deNOx technology, is a commercialized catalytic reaction used in combustion engines to convert unwanted nitrogen oxides into a benign mixture of nitrogen gas and water. NOx gases are pollutants that pose a hazard to human respiratory function and environmental ecosystems. Almost 50 % of NOx emissions originate from combustion engines used in transport, with a further 20 % arising from the stationary production of energy such as thermal power plants and industrial boilers. To address this, SCR, which has been shown to reduce NOx emissions by as much as 95 %, is currently used in diesel engine cars and trucks to meet emissions standards in Europe (Euro6), US (EPA Tier 2 and 3) and Southeast Asia. SCR occurs when NOx gases are flowed through an appropriately selected catalyst in the presence of a reductant such as ammonia. Small pore Cu-zeolites have been identified as excellent catalysts in the SCR reaction, being lauded for their unrivalled NOx conversion. Additionally, their strong performance in the highly topical low-temperature SCR (LT-SCR) region (i.e. ≤350 °C), and durability following hydrothermal ageing make them excellent candidates for vehicular SCR, and the current catalysts of choice for commercialized SCR in heavy goods diesel vehicles. However, an issue that is becoming increasingly recognized is the unwanted formation of N2O during SCR where small pore Cu- and Fe- zeolites are used as catalysts. Although historically exempt from emissions regulations due to their believed lack of toxicity, harmful indications following long-term exposure and a global warming potential almost 300 times that of CO2 mean that N2O will inevitably become the subject of increasingly exacting legislation beyond emissions standards. While pronounced formation of N2O has been experimentally observed previously, the mechanism by which this occurs is not completely understood and it is likely there is some degree of catalyst dependency. The widely reported disparity in N2O production based on framework type implies that not just the structure but the availability of certain copper co-ordination environments is crucially important in the formation of nitrate species at low temperatures. This research aims to explore in greater depth the relationship between the copper environment of the Cu-zeolite catalyst and its propensity for N2O formation.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз