Interaction of HNCO with Au(111) surfaces

Abstract

The surface chemistry of isocyanic acid, HNCO, and its dissociation product, NCO, was studied on clean, Odosed and Ar ion bombarded Au(111) surfaces. The techniques used are high resolution energy loss spectroscopy (HREELS) and temperature-programmed desorption (TPD). The structure of Ar ion etched surface is explored by scanning tunneling microscopy (STM). HNCO adsorbs molecularly on Au(111) surface at 100 K yielding strong losses at 1390, 2270 and 3230 cm − 1. The weakly adsorbed HNCO desorbs in two peaks characterized by T p = 130 and 145 K. The dissociation of the chemisorbed HNCO occurs at 150 K to give NCO species characterized by a vibration at 2185 cm − 1. The dissociation process is facilitated by the presence of preadsorbed O and by defect sites on Au(111) produced by Ar ion bombardment. In the latter case the loss feature of NCO appeared at 2130 cm − 1. Isocyanate on Au(111) surface was found to be more stable than on the single crystal surfaces of Pt-group metals. Results are compared with those obtained on supported Au catalysts.

Photocatalytic reduction of NO with ethanol on Au/TiO2

“…1C). Taking into account the results of extensive IR spectroscopic studies concerning the NO + CO catalytic reaction on different supported metals [37][38][39][40][41], and the adsorption of HNCO on TiO 2 , Au/TiO 2, and Au(1 1 1) surfaces [42][43][44], the band at $2180 cm À1 is ascribed to the vibration of NCO species bonded to Au particles, and the other one at 2206 cm À1 to the NCO attached to TiO 2 . The absorption feature at 2150 cm À1 very likely belongs to adsorbed CN group.…”

“…Considering the low reactivity of NCO group both on Au and TiO 2 [43,44], we do not consider that it could function as a real surface intermediate in the photocatalytic reduction of NO by C 2 H 5 OH at 300 K.…”