Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110).
The angular and velocity distributions of desorbing product N(2) were examined over the crystal azimuth in steady-state NO+CO and N(2)O+CO reactions on Pd(110) by cross-correlation time-of-flight techniques. At surface temperatures below 600 K, N(2) desorption in both reactions splits into two directional lobes collimated along 41 degrees -45 degrees from the surface normal toward the [001] and [001] directions. Above 600 K, the normally directed N(2) desorption is enhanced in the NO reduction. Each product desorption component, as well as CO(2), shows a fairly asymmetric distribution about its collimation axis. Two factors, i.e., the anisotropic site structures and the reactant orientation and movements, are operative to induce such asymmetry, depending on the product emission mechanism.
Off-normal emission of N2 and normal emission of N2O produced by the desorption mediated reaction of NO on Pd(110)
The spatial distribution of both N 2 and N 2 O produced at 490 K by the desorption mediated reaction of NO from Pd(l 10) was studied. The maximum emission of N 2 took place about 37° off-normal to the surface in the [001] direction, however, the desorption of NO and the emission of N 2 O obeyed cos θ and cos 2 θ, respectively. On the other hand, the spatial distribution of NO and N 2 toward the [110] direction obeyed cos 1.6 θ and cos 4.2 θ, respectively. In a flow of a mixture of 1 X 10 -8 Torr NO and 1 X 10 -6 Torr H 2 , a sharp N 2 peak at 490 K and a broad peak with a maximum at 600 K appear during TPR. A sharp N 2 peak at 490 K corresponds to the desorption mediated reaction of NO and a broad N 2 peak around 600 K is caused by the catalytic reaction of NO and H 2 . In the [001] direction, the former N 2 peak had a maximum at 37° off-normal to the surface, but the latter N 2 peak produced by the catalytic reaction obeyed cos θ.
Conserved Quantities of a Class of Nonlinear Difference-Difference Equations
Higher-order conserved quantities of a class of nonlinear difference-difference equations which are related to the discrete-time Toda equation are obtained using the Miura transformations.