Support effect on the structure and CO oxidation activity of Cu-Cr mixed oxides over Al 2O 3 and SiO 2

Abstract

Cu-Cr based catalysts supported on silica and alumina with 5 wt% total loading of (CuO + Cr 2O 3), in different molar ratios, were prepared by wet impregnation. The samples were studied by nitrogen adsorption isotherms (BET), temperature-programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Their catalytic activity was tested in the CO oxidation reaction. Different structures were obtained in dependence of the support, the atomic ratio and the calcination temperature. In particular, whereas on Al 2O 3 there was no experimental evidence for interaction between Cu and Cr, over the silica supported systems formation of new phases CuCr 2O 4 and CuCrO 2 occurred. Moreover, due to the different metal support interaction the increasing calcination temperature affected differently the surface segregation process of the two oxides. Indeed, at variance with the alumina case, Cu and Cr were found to segregate at the surface of the silica systems. The catalytic tests in CO oxidation indicated a synergetic effect between copper and chromium in the mixed oxides supported on silica and calcined at 500 °C. An increased calcination temperature affected negatively the activity due to surface sintering and formation of less active phases.