EFFECT OF SURFACE-AREA ON THE OXIDATION OF METHANE OVER SOLID OXIDE SOLUTION CATALYST LA0.8SR0.2MNO3

Solid oxide solutions of the type La0.8Sr0.2MnO3 with BET surface area s of 28, 20, 12, and 8 m(2)/g were prepared by sintering at 700, 800, 900, and 1000 degrees C, respectively. The catalysts were tested for m ethane total oxidation in a fixed bed reactor with feed containing 0.2 8% CH4, 12% O-2, and the balance helium. The activity of methane at 55 0 degrees C was found to decrease from 0.7 mu mol/s . g to 0.2 mu mol/ s . g with the decrease in the surface area (28 and 8 m(2)/g, respecti vely) of La0.8Sr0.2MnO3. Temperature programmed desorption studies ind icate that the amount of oxygen desorbed on these La0.8Sr0.2MnO3 oxide s decreased from 15 to 0.8 mu mol/g with the decrease in the surface a rea. X-ray photoelectron spectroscopy studies revealed a decrease in t he Mn surface concentration for the samples sintered at 700 to 1000 de grees C. The oxidation of methane on La0.8Sr0.2MnO3 was found to corre late with the surface area, i.e., facile, the surface concentration of Mn, and the oxygen properties of the oxides. (C) 1996 Academic Press, Inc.