Decomposition of NO on tungsten carbide and molybdenum carbide surfaces

The decomposition of (NO)-N-15 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 (NO)-N-15 occurs readily over all surfaces, and the only N-15-containing reaction products are N-15(2) and (N2O)-N-15 under our experimental conditions. Much higher surface reactivity for (NO)-N-15 decomposition was observed over the more open structured C/W(111) surface, with a value of 0.68 (NO)-N-15/W, in contrast to the surface reactivity of 0.24 (NO)-N-15/W over the close-packed C/W(110) surface. The selectivity of these two N-15-containing reaction products depends on the structure of the substrates as well. The more open-structured C/W(111) surface favors the production of N-15(2), with a product selectivity of N-15(2) being approximately 87%. In contrast, the selectivity to N-15(2) is only about 52% on C/W(110). In addition, we have investigated the decomposition of (NO)-N-15 on C/Mo surfaces that were epitaxially grown on W(111). The selectivity of N-15(2) on C/Mo/W(111) surfaces is similar to 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.