Effect of H2S poisoning on the i.-r.-spectrum of CO and COS adsorbed on alumina-supported platinum

Abstract

An i.-r. investigation has been conducted to determine the effect of H₂S poisoning on CO- and COS-covered γ-alumina-supported platinum surfaces. The chemisorption of CO on a “clean” surface resulted in the formation of a sharp band at 2080 cm^–1. Adsorption of H₂S on a CO-covered surface drastically decreased the intensity of the 2080 cm^–1 band, and produced a weak band at 2170 cm^–1. Adsorption of CO on an H₂S-poisoned platinum surface showed bands at 2170, 2080, and 2060 cm^–1. The 2170 cm^–1 band disappears with evacuation; it is attributed to CO weakly adsorbed on sulphur-poisoned sites.

COS adsorption on platinum resulted in the formation of bands at 2080, 2050, 1995, 1950 and 1920 cm^–1. The 2080 cm^–1 band is due to the decomposition of COS on platinum at room temperature. The three bands at 2050, 1995 and 1950 cm^–1 disappeared with evacuation and are presumably due to the weakly chemisorbed COS on “clean” or sulphur-poisoned platinum sites. The chemisorption of CO on a COS-covered surface results in the decrease of intensity of the 1920 cm^–1 band. Addition of H₂S to a COS-covered surface caused a more rapid disappearance of the 1920 cm^–1 band than the 2080 cm^–1 band. The formation of the 1920 cm^–1 band is attributed to the CO stretching of the chemisorbed COS molecule on a “clean” platinum site.