SURFACE-COMPOSITION OF IRON-OXIDE CATALYSTS USED FOR STYRENE PRODUCTION - AN AUGER-ELECTRON SPECTROSCOPY SCANNING ELECTRON-MICROSCOPY STUDY

The surface composition of two different types of potassium promoted i ron oxide catalysts used for styrene production was studied with Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). C atalyst A was studied after use in ultrahigh vacuum mass spectrometry (MS)-desorption experiments at temperatures close to ordinary process temperatures of 860-890 K. The loss of surface reactivity observed in the MS experiments seems to be connected to formation of KOH rather th an to extensive loss of K from the catalyst. Catalyst B had been used in the industrial styrene process prior to the AES studies. The normal migration processes are confirmed. We also observe a low oxygen conte nt, which indicates formation of K not bound as an oxide. Loss of oxyg en should irreversibly decrease the amount of the active compound KFeO 2, and may thus be an important early step in the deactivation of the catalyst.