Anisotropic velocity distribution of desorbing product in carbon monoxide oxidation on palladium (110)

Abstract

Significant anisotropy was found in the velocity distributions of desorbing product CO, from a Pd( 110) surface. The velocity distributions were determined by a cross-correlation time-offlight technique combined with angle-resolved thermal desorption. Heating the coadlayer of CO and oxygen produces five peaks in the CO, formation spectrum; P,-(around 420 K), P2-(-370K),P,-(-3300K),P,-(-230K),andP,-CO,(-l70K).Thetranslational temperature of each CO* is much higher than the corresponding surface temperature, and increases in the sequence of P,-< P2-< P3-< P4-< P,-CO,. It decreases rapidly with an increase in the desorption angle perpendicular to the surface trough and more slowly parallel to it. This anisotropy is correlated to the reaction site symmetry.

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110)

“…This anisotropy is very close to that in the CO+O 2 reaction on Pd͑110͒. 37 The normally directed N 2 desorption is approximated by a cos 7 ␣ cos 2 ␤ form. The distribution is commonly sharper in the plane along the ͓001͔ direction.…”

“…4 On the other hand, no inclined CO 2 desorption has been found on Pd͑110͒ under either TPD or SS conditions, although the c͑2 ϫ 4͒-O lattice due to the missing-row structure was observed. 37,40 The lack of inclined CO 2 desorption on this surface is due to either the instability of the ͑1 ϫ 2͒ reconstruction without oxygen above 355 K, 47 or high oxygen coverage. The CO 2 desorption shifts to the surface normal direction when the ͑1 ϫ 2͒ surface is highly covered by oxygen.…”

“…This anisotropy is also similar to that in the CO oxidation. 37 It is interesting to examine the extent of anisotropy of the normally directed N 2 desorption. The deconvolution into the three components could be well performed for the data at 640 K as shown in Fig.…”

Angular dependence of rotational and vibrational energies of product CO2 in CO oxidation on Pd(110)

“…It was proposed that CO approaches an oxygen atom at the bottom of the atomic trough to react on this surface. 6,30 The present results suggest that the TS is oriented in the y-z plane and that it receives repulsion along the z-axis, resulting in rotational motion in the y-z plane. In this case, nascent CO 2 can easily move in the y-z plane, but its motion in the x-z plane is hindered by rows of the 1st Pd layers.…”

An Experimental Approach to Transition States of Surface Reactions; Energy Partitioning in Repulsive Desorption

“…1: Three-dimensional spatial distributions on Pd(110) of (a) desorbing product CO2 in CO oxidation under TPD conditions [8] and of (b) N2 in a steady-state N2O+CO reaction at 520 K [9].…”