抄録
We have observed that activities of H2-D2 exchange reaction and 1,3-butadiene hydrogenation were enhanced on ZnO catalyst by thermal treatment under ultrahigh vacuum (UHV : pressure ≤ 10-7 Pa). Temperature programmed desorption (TPD) of adsorbed H2 was carried out over ZnO thermally treated under UHV and low vacuum (LV≈ 1 Pa). Hydrogen was adsorbed on the catalysts at room temperature or 473 K. On the LV-treated ZnO at 873 K (873-LV), two desorption peaks were observed at 650 and 800 K. On the UHV-treated ZnO at 873 K (873-UHV), a new desorption peak was observed in the range between 360 and 480 K in addition to the peaks observed on 873-LV. TPD over the surface on which H2 and D2 were co-adsorbed was carried out in order to determine whether each desorption peak came from dissociatively or molecularly adsorbed hydrogen. In the range between 360 and 480 K, remarkable desorpion peak of HD was observed on 873-UHV, whereas almost no desorption peak of HD was obserbed on 873-LV. The desorption peak of H2 at 550 K was accompanied with HD desorption on 873-UHV in the case that the adsorption was carried out at 473 K. Therefore the desorption peaks at 360 and 550 K were ascribed to desorption of H2 adsorbed on 873-UHV dissociatively. The desorption peak of H2 at 620 K was not accompanied with HD desorption on 873-UHV in the case that the adsorption was carried out at room temperature. Therefore the peak at 620 K was ascribed to desorption of H2 adsorbed on 873-UHV molecularly. These results suggest that new active sites which readily dissociate molecular H2 were generated by the UHV-treatment of ZnO.
