Transition metal catalysts for the conversion of ortho- to para-hydrogen.

摘要

The chemistry of the catalytic conversion of ortho- to para-hydrogen was pursued in this study by the preparation and characterization of transition metal silicates as well as ruthenium supported on silica.; A plug flow reactor system was designed to test the conversion of ortho- to para-H{dollar}sb2{dollar} from room temperature to {dollar}-{dollar}196{dollar}spcirc{dollar}C. This involved both the design and modification of an overall reactor system as well as individual reactor tubes. The system was calibrated to allow the measurement of conversion by thermal conductivity and measured catalytic activity such that they could be compared with other catalysts in the literature.; Metal silicates of nickel, iron, chromium, and manganese were prepared by the coprecipitation or sol-gel methods. The study involved the optimization of activities at {dollar}-{dollar}196{dollar}spcirc{dollar}C by the variation of the catalyst preparation method. These changes, which increased the total surface area and total pore volume of the silicate, also increased the activity. Nitrogen adsorption confirmed the changes in the physical structure of the silicate.; Ruthenium catalysts were prepared through traditional impregnation methods as well as through impregnation of a ruthenium ammine intermediate. It was found that the traditional catalysts had a maximum activity at {dollar}{lcub}approx{rcub}{lcub}-{rcub}{dollar}158{dollar}spcirc{dollar}C. This is most likely caused by the increasing strength of the Ru-H interaction at decreasing temperatures.; Activity could be increased by heating the catalyst to high temperature and then cooling to the reaction temperature in helium. High temperature is felt to desorb a strongly bound hydrogen layer, while low temperature cooling does not allow as great of a readsorption of hydrogen. Chlorine containing precursors enhance this effect by residual surface chlorine increasing the strong H{dollar}sb2{dollar} adsorption activation energy.; Ruthenium ammine catalysts showed greatly enhanced activities relative to the traditionally prepared ruthenium catalysts. This increase is caused by increased dispersion of the ruthenium particles, as determined by hydrogen adsorption studies. The ammine catalysts were inactive if chlorine was present during the final drying of the catalyst. This can be resolved by using a non-chlorine containing ruthenium precursor or washing the wet catalyst with aqueous ammonia.