EPR INVESTIGATION AT 4K OF CERIA AND Cu-Ce OXIDE UNDER SO_2 AND H_2 ATMOSPHERE

摘要

Ceria and copper-ceria catalysts have been investigated by EPR at 4K after a treatment under controlled atmosphere. An asymmetric EPR spectrum with g_1=3.9702, g_2=0.6256 and g_3=0.5285 has been observed for a Ce_2(SO_4)_3 sample. The EPR parameters of this signal are typical for the ions having the electronic 4f~1 configuration (Ce~(3+) ions). The copper-cerium oxide sample, treated under SO_2 atmosphere, exhibits a signal, centred at g=2.166 with AH=280 Gauss, relative to the formation of CuSO_4 phase. Under a mixture of He + H_2, the Cu (Ⅱ) species of the copper-cerium catalyst are progressively reduced into Cu~+ and Cu° Two transitions corresponding to the fine structure of an EPR signal were evidenced and attributed to Cu°dimers in the ceria matrix. All these results were confirmed by means of computer simulation.