ADSORPTION OF H-2, O2, CO, AND CO2 ON A GAMMA-ALUMINA - VOLUMETRIC AND CALORIMETRIC STUDIES

Volumetric and microcalorimetric measurements of the adsorption of H-2 , O2, CO, and CO2 on gamma-Al2O3 have been carried out. Amounts adsorb ed at different temperatures in the range 195-673 K have been determin ed as a function of pressure and time. Heats of adsorption vs coverage have been measured at 315 K, and in some cases also at 263 K. Hydroge n and oxygen adsorbed weakly on gamma-alumina; an activated, somewhat stronger adsorption of these two adsorbates appeared at 300-400 K, and a highly activated oxygen reaction with the alumina surface began at around 573 K. Carbon monoxide adsorption was stronger than that of hyd rogen or oxygen, and reached higher coverages. CO adsorption was mostl y due to a weak surface carbonyl bond although formate species also ap peared on the surface. Carbon dioxide adsorption on gamma-alumina prod uced three energetically different species which were identified with the help of infrared spectroscopy data as (1) very strongly held surfa ce carbonate, (2) surface bicarbonate formed by reaction with, and who se number therefore depends on the number of, hydroxyl groups, and is slowly converted into carbonate, and (3) weakly adsorbed CO2. Adsorpti on calorimetry results give support to the conclusions obtained from t he analysis of volumetric isotherms, showing that isotherms themselves can yield valuable information on several details of the adsorption p rocess.