Surface reactivity of reduced LaFeO3 as studied by TPD and IR spectroscopies of CO,CO2 and H2

CO, CO₂ and H₂ reactive adsorption on LaFeO₃ at 298 K has been studied as a function of the reduction temperature of the perovskite oxide by means of temperature programmed desorption (TPD) and infrared (IR) spectroscopies. TPD spectra of CO after CO adsorption contained peaks at 365 to 440 K assigned to linearly adsorbed CO and at 495 to 540 K assigned to bridged CO. TPD spectra of CO₂ after CO adsorption presented broad peaks centred at 570 and 715 K assigned to monodentate and bidentate carbonates, respectively. TPD spectra of CO₂ obtained after CO₂ adsorption contained peaks at 375 to 425 K and at 570 to 675 K. These were associated to infrared bands of monodentate and bidentate carbonates, respectively. In the CO-H₂ and H₂-CO successive adsorption on the reduced surface of LaFeO₃ the TPD peak of H₂ at 345 to 360 K is strongly inhibited and a new desorption peak appeared at 585 to 590 K. This is assumed to be due to CO adsorption on metallic Fe⁰ sites (CO-H₂ coadsorption) or to a displacement of adsorbed hydrogen from Fe⁰ to a new adsorption site (H₂-CO coadsorption). CO was found to interact more strongly than hydrogen with the adsorbent surface.Deceased, formerly of Instituto de Catálisis y Petroleoquímica, C.S.I.C., Serrano 119, 28006 Madrid, Spain.