Abstract: The reduction behavior of CuO supported on SnO_2, ZnO and Al_2O_3 has been examined, the effect of support and Pd investigated as well. The catalyst samples were studied by TPR and electric conductivity measurement simultaneously.
It was observed that CuO supported on n-type semiconductor oxides SnO_2 and ZnO was more easily reduced than bulk CuO and that on Al_2O_3. The TPR peak of CuO was shifted from 285 ℃ to 210 ℃ and 240 ℃ when supported on SnO_2 and ZnO respectively. By introducing a small amount of Pd (0.4-0.5 Wt.%) onto the catalyst, the reduction peak was further shifted to below 100 ℃ in the case of SnO_2 and by 50-60 ℃ in the case of ZnO.
The conductivity-temperature curve of SnO_2 and ZnO in Ar-H_2 (5%) atmosphere revealed that the n-defects were promptly generated around 200-250 ℃, it was the same temperature region at which the reduction of CuO on these supoorts occurred.
In the presence of Pd additve the onset of conductivity increasing would be observed on SnO_2 and ZnO by exposure to reducing atmosphere even at room temperature, while for CuO/SnO_2 and CuO/ZnO the abrupt change of conductivity occurred around 100-150 ℃. Thus it was reasonably explained that Pd, being an activator for H_2 molecules, promoted the defect generation in semicoductor and in turn the reduction of supported CuO was further enhanced. Noticeably in the case of the occurrence of CuO reduction the electric conductivity change of semiconductor was moderated, it seemed that the negative charge was transferred from support to CuO.
As for the catalyst with Al_2O_3 as support, in accordance with that Al_2O_3 was an insulator, no charge transfer property and no promoting effect on CuO reduction was observed at all.
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Project supported by the Science Fund of Chinese Academy of Sciences