An infrared spectroscopic study of the adsorption of carbon monoxide on silica-supported copper particles

Abstract

Infrared spectroscopy is used to study the adsorption of carbon monoxide (20°C; 0.1– 100 Torr) on copper-on-silica catalysts differently prepared and pretreated. As determined by electron microscopy and X-ray line broadening, the catalysts contain copper particles having sizes of 60 to 5000 Å depending on the preparation procedure and the thermal treatment. Adsorbed carbon monoxide displays broad infrared absorption bands exhibiting a maximum at 2099 to 2146 cm-1. The position of the maximum varies with the preparation and pretreatment of the catalyst. With deposition-precipitated catalysts (Cu-particles 60–120 Å) prolonged reduction at 300°C causes the maximum to shift from 2104 to 2139 cm-1. The shift is attributed to initial facetting and subsequent rounding of the small copper particles. An impregnated catalysts (40–5000 Å) shows a shift from 2146 to 2129 cm-1 upon more severe reduction, which is ascribed to sintering to large copper particles.