Hydrogen Adsorption and H₂-D₂ Exchange on a Molybdenum Nitride Catalyst

Abstract

The hydrogen adsorption on a molybdenum nitride catalyst and the H₂-D2 exchange catalyzed by the catalyst have been studied at 95°C and 8°C. The H₂-D2 exchange proceeded even at 95°C. The amount of adsorption of hydrogen was 3.5 x 1014 molecules cm^-2 at 95°C and 200 mmHg, corresponding to about a half of that of nitrogen for mono-molecular layer adsorption. Deuterium was adsorbed more than hydrogen under the same conditions. The effects of preadsorbed ammonia and of preadsorbed carbon monoxide on the hydrogen adsorption and on the Ha-D, exchange were investigated. Ammonia was strongly adsorbed on the catalyst at room temperuture, the amount of adsorption being 3.0 x 1014 molecules cm^-2. The amount of hydrogen adsorbed at 95°C decreased linearly with the increase of the amount of ammonia preadsorbed at room temperuture. The activity for H₂-D2 exchange at 95°C decreased drastically at an amount of ammonia preadsorbed of 2.4 x 10" molecules cm^-2, as shown in Fig.3. Carbon monoxide was also adsorbed strongly on the catalyst at room temperuture, the amount of adsorption being 1.6 x 1014 molecules cm^-2. Preadsorption of carbon monoxide reduced the amount of hydrogen adsorbed and the activity for 1-12-D, exchange at 95°C, as shown in Fig.6. The 1-12-D2 exchange activity of the adsorbed hydrogen and the properties of the active site were discussed. It is concluded that only a small fraction of the adsorbed hydrogen can participate in the Hz-D. exchange.