No abstract

Catalysts having similar chemical compositions were tested for the isomerization of C7 paraffins, mainly branching of n-heptane. The principal objective was to maximize isomerization at minimal hydrocracking levels. Catalysts were prepared using commercially available zeolites with some modifications. Metals (mainly platinum) were incorporated in the conventional way (dispersed metal) but also as organometallic complexes. Initial activity tests used a stirred batch autoclave while time on stream tests used an automated continuous flow tubular microreactor. Products were analyzed by gas chromatography. Model compounds included other C7 hydrocarbons such as 2,4-dimethylpentane, methylcyclohexane, and toluene. A prototype catalyst provided 66% n-heptane isomerization with only 4% cracking per pass at high space velocities (LHSV = 5). Its selectivity was similar to that of a highly active commercial alumina-based catalyst while showing an improved tolerance for aromatic hydrocarbons and a longer catalyst life. Simple kinetic models were examined and used to simulate the sequence of events on the catalyst surface.

Tritium producing burnable absorber rods (TPBAR) are used for production of the hydrogen isotope tritium (H 3 ) which is used for various national security applications. These rods are formed by concentric cylindrical layers, as shown in Figure1a; the main functional parts being an outer steel cladding for support, a zircaloy getter, and the LiAlO2 pellet layer from which the tritium is converted. For production of tritium, these rods are placed in reactors and irradiated with neutrons which, in the pellet, convert the Li 6 to He 4 and H 3 . This irradiation causes large changes in the microstructure. While as-fabricated pellets are typically porous, particularly around grain boundaries, after irradiation, pellets become porous near the center of the grains (Figure1b and 1c), with pores on the scale of ~1um or smaller. Since differences in pore formation can significantly affect the performance of a bulk material, it is imperative to characterize the development of the pores that form during irradiation[1]. To capture the morphology and networking of these pores and grain boundaries, a 3D mapping technique with resolution on the nanoscale is needed.