Chromia/alutuina catalysts with different metal loading were characterized using X-ray photoelectron spectroscopy (XPS), proton induced X-ray emission (PIXE) and thetmogravimetric (TG) techniques to elucidate the surface structure of these catalysts. XPS studies on calcined samples show a sharp increase of the Cr/Al ratio at calcination temperatures up to 500Β°C while the ratio remains relatively unchanged at higher calcination temperature. The surface state of chromium shows predominantly CP'. At calcination temperatures higher than SM'C, calcination-induced reduction is observed of the CP' to C?', where the fraction of chromia in Cti' oxidation state increases with increasing temperature. A progressive increase of the intensity of the peak due to Cr 2p of the C? + oxidation state is also observed with increasing amount of metal loading. The calcination-induced reduction of the alumina-supported chromia was found to be less than the corresponding reduction of bulk Cr&. Also, the size of the spin-orbit splitting of the Cr 2p level of chromia catalysts which had undergone calcination-induced reduction was found to be smaller than would be expected for bulk C8'. The XPS spectra of chromium on the Cr/Al catalysts were found to be time dependeht. Photoreduction of CP' on Cr/Al samples was found for irradiation times longer than 4.0 min. It was found from PIXE analysis that at higher calcination temperature, the Cr/Al atomic ratio approaches the values obtained by XPS. For all samples, the chromium particles were found to be homogeneously distributed on the alumina support for calcination temperatures up to 800Β°C. Thermogravimetric results on uncalcined bulk CrG3 agree well with the XPS observation as to the fact that the main phase transformation of Cfl' compounds occurs at about 500Β°C. resulting in reduction to CP'.