THERMAL-BEHAVIOR OF A RH/AL2O3 MODEL CATALYST - DISAPPEARANCE OF SURFACE RH UPON HEATING

The thermal behavior of a Rh/Al2O3 model catalyst has been investigated under ultrahigh-vacuum conditions by Auger electron spectroscopy (AES), high-resolution electron energy loss spectroscopy (EELS), and carbon monoxide capacity using thermal desorption spectrometry (TDS). Our results indicate that, upon heating the Rh/Al2O3 to 1100 K (825°C), the capacity for CO chemisorption is completely lost as Rh is observed to move from the top surface layer, either by the diffusion of Rh into the bulk Al2O3 or via covering by a thin Al2O3 film, while remaining in the near surface region. The formation of large clusters of rhodium upon heating is not consistent with our data. These findings appear to relate to the behavior of high surface area supported Rh/Al2O3 catalysts heated to high temperature. © 1990 American Chemical Society.