Henry H. Hwu

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.