ADSORPTION OF NITRIC OXIDE ON CHROMIA SUPPORTED ON ALUMINA

Adsorptive properties of chromia supported on alumina have been studied with an electrobalance for NO as an adsorbate. Isotherms are presented in the range from -78 ° to 150 °C for both an oxidized and a reduced surface. The isotherms are of the Freundlich type at pressures between 0.1 and 300 torr. Maximum coverage corresponds to approximately one molecule of NO per atom of chromium in the surface. The adsorption of NO can therefore be used to assess the actual chromia surface in the presence of a support material. Changes in pressure and temperature influence the coverage on an oxidized surface more strongly than on a reduced surface. Kinetic measurements at constant temperature and pressure show a significant difference between an oxidized and a reduced chromia surface. In the first case a uniform decrease of the adsorption rate with time is observed, while in the second case a fast initial adsorption is followed by a much slower process, indicated by a sharp break in the corresponding Elovich curves. The kinetic parameters as well are influenced by temperature more strongly for the oxidized than for the reduced state. An attempt is made to relate these chemisorption results to the catalytic behavior of supported chromia for the reduction of NO. © 1969.