Studies of the hydrogen held by solids. XX. The chromatographic separation of the isotopic and allotropic hydrogens on alumina and fluorided alumina

Abstract

Chromatographic separation factors and retention times have been determined for the hydrogen allotropes and isotopes over pseudoboehmite, ν + γ alumina, and fluorided alumina columns. Measurements were made as a function of the extent of dehydroxylation of the surface, pulse size, and the fluoride level. With all preparations, the retention times and separation factors decreased with increasing pulse volume. With pseudoboehmite, the retention times of ortho and para-H 2 increased rapidly as the catalyst was dehydroxylated and converted into the transition aluminas. Separation factors increased with retention times for pretreatment temperatures up to about 350°C, where the ortho-para separation collapsed as the allotropic conversion reaction became faster than the separation. A related, but somewhat different, behavior was exhibited by fluorided aluminas and the transition alumina after storage. With these materials the retention times and separation factors remained nearly constant up to a critical pretreatment temperature, where the separation collapsed; at still higher pretreatment temperatures the retention times increased sharply. With fluorided aluminas the effects of the ortho-para conversion reaction and the sharp increase in retention time set in at lower pretreatment temperatures, the higher the fluoride content. The hydrogen isotopes were used to extend the measurements to higher pretreatment temperatures where the allotropes could not be separated. With HD the retention times continued to increase as the catalyst was dehydroxylated to the point where the test pulse was virtually irreversibly chemisorbed by the column; separation factors were also increased substantially. The separation factor data were used to estimate lower limits of the magnitude of the electric field emanating from the strongest sites. A maximum value of 2.67 volts/Å was calculated. Selective poisoning with CO 2 was used to identify the sites used in the separations with those which effect the ortho-para hydrogen conversion.