The stability of NCO species bonded to Pt, Rh and Pd produced by isocyanic acid (HNCO) adsorption has been investigated by infrared spectroscopy. Adsorption of HNCO on supported metals at 190 K produced an intense band at 2180 cm-1 which is attributed to the asymmetric vibration va of NCO formed in the dissociative adsorption of HNCO on the metals. This band started to attenuate above 200 K, partly due to the decomposition of NCO into adsorbed CO and N, and partly due to the migration of NCO from the metals onto silica. These processes are indicated on the ir spectra by the appearance of absorption bands due to Si-NCO and M-CO species. The 2180 cm-1 band indicative of the presence of metal-NCO species was completely eliminated at 350 K on Pd, 400 K on Pt and 425 K on Rh. Oxygen treatment of the supported metals, however, greatly enhanced the stability of NCO on the metals.
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