Paul Joseph Andersen

Decomposition of NO on tungsten carbide and molybdenum carbide surfaces

The decomposition of 15NO on C/W(111), C/W(110), and on monolayer and bulk C/Mo/W(111) surfaces is compared based on temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES) measurements. Our results indicate that the decomposition of 15NO occurs readily over all surfaces, and the only 15N-containing reaction products are 15N2 and 15N2O under our experimental conditions. Much higher surface reactivity for 15NO decomposition was observed over the more open-structured C/W(111) surface, with a value of 0.68 15NO/W, in contrast to the surface reactivity of 0.24 15NO/W over the close-packed C/W(110) surface. The selectivity of these two 15N-containing reaction products depends on the structure of the substrates as well. The more open-structured C/W(111) surface favors the production of 15N2, with a product selectivity of 15N2 being approximately 87%. In contrast, the selectivity to 15N2 is only about 52% on C/W(110). In addition, we have investigated the decomposition of 15NO on C/Mo surfaces that were epitaxially grown on W(111). The selectivity of 15N2 on C/Mo/W(111) surfaces is ∼88%, which is very similar to that observed on C/W(111). Finally, the general similarity between the DeNOx chemistry on carbides and on Pt-group metals will also be discussed.

Performance of NOx Adsorber Emissions Control Systems for Diesel Engines

Increasingly stringent Diesel vehicle emissions legislation around the world means that advanced aftertreatment systems may be required to achieve the required nitrogen oxide (NOx) emissions rather than through engine control measures alone. As in lean-burn gasoline applications, NOx adsorber systems offer great potential for high level NOx conversion in Diesel exhaust, and their use on Diesel engines is an area of intense interest for possible use in light-duty and heavy-duty applications. This paper is concerned with the performance of advanced NOx adsorber catalysts developed specifically for the requirements of light-duty Diesel vehicles. Laboratory and engine bench data are discussed that demonstrate NOx conversions in excess of 90% over a wide temperature window can be achieved. The durability characteristics of these catalysts are also reported. The ability to tune the NOx adsorber formulation to an operating window for a specific application and/or position in the exhaust is important for the optimisation of a full emissions control system. This paper presents operating temperature windows of some optimised NOx adsorber catalysts for maximisation of the operating window at low and high temperatures.

High-temperature scr catalyst

A catalyst comprising: (a) a microporous crystalline molecular sieve comprising at least silicon, aluminium and phosphorous and having an 8-ring pore size; and (b) a transition metal loaded in the molecular sieve, the transition metal loading is less than about 1 wt %.