Surface interactions between coadsorbed ammonia and carbon monoxide on the Pt(111) surface

Abstract

Interactions between coadsorbed species were studied for the NH 3/CO/Pt(111) system using temperature-programmed desorption (TPD). Coadsorbed CO has a strong effect on the high-temperature ammonia desorption spectrum. For saturation CO precoverage, two distinct high-temperature peaks are observed at 260 and 325 K. In contrast, on a clean Pt(111) surface, ammonia desorption produces a broad, flat plateau from 200 to 375 K. For intermediate CO coverages, the two high-temperature peaks grow and merge into a single ammonia desorption peak at 295 K. CO and NH 3 compete for sites on the Pt(111) surface, with CO inhibiting ammonia-ammonia interactions. Coadsorbed CO does not have a pronounced effect on the low-temperature high-coverage desorption of ammonia. This hydrogen-bonded ammonia desorbs at the same temperatures from both clean and CO-modified Pt(111) surfaces; however, the saturation coverage is reduced. Ammonia does not displace adsorbed CO at 125 K, and no ammonia decomposition is observed.