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

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1993

OSTI ID:7036760

Brooks, C J

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[sub 2] from room temperature to [minus]196[degrees]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 [minus]196[degrees]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 inpregnation of a ruthenium ammine intermediate. It was found that the traditional catalysts had a maximum activity at [approx][minus]158[degrees]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[sub 2] adsorption activation energy. Ruthenium ammine catalysts showed greatly enhanced activities relative to the traditionally prepared ruthenium catalysts.

• Research Organization: Iowa Univ., Iowa City, IA (United States)
• OSTI ID: 7036760
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
AMMINES
CATALYTIC EFFECTS
CHLORINE COMPOUNDS
CHROMIUM COMPOUNDS
CHROMIUM SILICATES
COMPLEXES
CONVERSION
ELEMENTS
HALOGEN COMPOUNDS
HYDROGEN
IRON COMPOUNDS
IRON SILICATES
MANGANESE COMPOUNDS
MANGANESE SILICATES
NICKEL COMPOUNDS
NICKEL SILICATES
NONMETALS
OXYGEN COMPOUNDS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS