Surface and catalytic properties of gamma-irradiated Fe2O3-Cr2O3/Al2O3 solids

An iron, chromium, aluminium mixed oxides specimen having the nominal molar composition 0.125 Fe2O3 0.06 Cr2O3/Al2O3 was prepared and subjected to the rmal treatment at 700 degrees C. The calcined sample was exposed to differe nt doses of gamma-rays varying between 20 and 160 Mrad. The surface and cat alytic properties of the different irradiated solids were studied using nit rogen adsorption at - 196 degrees C and catalysis of CO oxidation by O-2 at 225-300 degrees C. The results showed that gamma-irradiation at doses betw een 20 and 80 Mrad resulted in a progressive increase of specific surface a rea (10-36%), total pore Volume (55-175%) and mean pore radius (41-105%) of treated adsorbents. Irradiation at doses above this limit led to a signifi cant decrease in the magnitudes of different surface parameters which still measured higher values than those found for the un-irradiated sample. The catalytic activity increased monotonically as a function of the dose absorb ed. The catalytic reaction rate constant, measured at 225, 250 and 300 degr ees C increased by 400, 170 and 115%, respectively by exposure to a dose of 160 Mrad. The increase in the reaction rate constant per unit surface area measured at the same reaction temperatures due gamma-irradiation at 160 Mr ad was 370, 155 and 102%. This treatment did not modify the mechanism of th e catalytic reaction, but increased the number of catalytically active site s taking part in chemisorption and catalysis of CO oxidation reaction witho ut changing their energetic nature. (C) 1999 Elsevier Science B.V. All righ ts reserved.