The activation of yttria, lutetia, and ytterbia for the ortho-parahydrogen conversion

Abstract

Abstract The diamagnetic oxides Y2O3 and Lu2O3 may be activated for the p-H2 conversion by heating them in H2 between 823 and 973 K. This pretreatment appears to generate the ions Y2+ and Lu2+, respectively. From the quantity of water formed during the activation it is possible to estimate the surface concentration of paramagnetic sites. By combining this information with the specific conversion rates it is possible to obtain the net conversion rate per active site. The results are in agreement, to about one order, with recent theoretical calculations of the absolute rates. From conversion rate studies over Lu2O3 and Yb2O3 and from extrinsic field studies, it is concluded that heating Yb2O3 in H2, and possibly other rare earths in the C crystallographic form, causes surface reactions resulting in a 4fn5d0 → 4fn5d1 electronic change rather than 4fn5d0 → 4fn+15d0.