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The direct radiative capture reactions D(p,⋎)He³ and O¹⁶(p,⋎)F¹⁷, both of which are of interest in astrophysical processes, have been studied theoretically using a simple two-body direct radiative capture model in order to estimate the cross sections at low energies. In addition, the time inverse of the first reaction, namely the photodisintegration of He³, has been studied for high excitation energies in He³ by applying the reciprocity relations to the direct capture theory. The calculations involve taking matrix elements of the particle-radiation interaction Hamiltonian between bound and continuum states and using first-order perturbation theory to obtain the cross sections. Bound state wave functions are generated in simple potentials involving square-well and Saxon-Woods forms with appropriate Coulomb barriers and with one free parameter which is adjusted to fit the binding energy. The potential parameters for the continuum state wave functions are adjusted to fit available scattering data. For the reaction O¹⁶(p,⋎)F¹⁷ the cross sections for transitions to both the ground and first excited states are in good agreement with the somewhat limited experimental data from 150 KeV to 2.5 MeV and the astrophysical S-factors are shown to be energy dependent even at energies below 100 KeV. The photodisintegration cross section for the reaction He³(⋎,p)D is well fitted in the neighbourhood of the peak at around 11 MeV as well as at lower energies. The D(p,⋎)He³ direct capture cross sections in the energy range around 1 MeV are shown to be sensitive to admixtures of ²S-state of mixed symmetry and of ⁴D-state in the ground state of He³, which is predominantly Symmetric ²S. The same model including the ²S-state of mixed symmetry leads to a capture cross section for thermal neutrons by deuterons in good agreement with the experimental value. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The reaction, ⁷Li(³He,dα)⁴He, is proposed to search for an asymmetry about the direction of motion of ⁶Li in the breakup of the 4.57 MeV excited state of this nucleus as an intermediate state. This follows after the discovery in 1967 by Reimann et. al. of such an asymmetry about the direction of motion of ⁵Li in the breakup of the ground state of this nucleus, as an intermediate state in the reaction, ⁶Li(³He,pα)⁴He. The purpose of these experiments is to attempt some understanding of the three-body reaction mechanisms involved, and the manner in which the various particles are correlated in the intermediate state. The three-body kinematics of the reaction, ⁷Li(³He,dα)⁴He were thoroughly investigated, and because of particle identification problems, a charged particle time-of-flight technique was proposed to distinguish the emitted deuterons from alpha particles. A 23 inch scattering chamber was designed and constructed for this and other work, and subsequently tested using the reaction ⁷Li(p,α)⁴He. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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<p>  </p> <p>Dehydrogenation is a common reaction used to upgrade paraffins to olefins in the chemical and oil industries. Given the increased abundance of inexpensive alkanes due to the worldwide shale gas boom, this reaction has become increasingly important. Conventional industrial techniques such as thermal cracking and steam cracking have relatively poor olefin selectivity and thus require energy-intensive separations. Industry is increasingly relying on catalytic dehydrogenation as a more environmentally friendly alternative to generate olefins. While recent development in catalyst materials has largely solved issues with activity and selectivity, issues with catalyst stability remain. Deactivation mechanisms such as coke formation and phase changes plague the short-term and long-term stability of these catalysts, often requiring frequent and intensive regeneration procedures. </p> <p>This thesis will explore several strategies for mitigating the deactivation of dehydrogenation catalysts. This includes the modification of catalyst properties and reaction conditions, such as the catalyst support and the use of H2, to mitigate coke formation and even regenerate catalyst materials non-oxidatively, thus increasing the catalyst lifetime. Secondly, this thesis will cover the discovery of new catalyst materials through computational predictions based on descriptors assessed from several previous works. Experimental validation of these predictions led to the discovery of several new Rh and Ir based alloy materials that are remarkably selective and stable for propane dehydrogenation (PDH). Lastly, the contribution of electronic structure of PDH catalysts will be assessed using a new characterization technique that will help relate catalyst properties to catalyst performance and stability. </p> <p>Several advanced X-ray synchrotron techniques have assisted the analysis and discovery of catalyst materials in this work. Particularly, this includes difference-EXAFS to assess the surface structure of alloy catalyst materials as well as the newly-developed non-resonant X-ray emission spectroscopy (NR-XES) to assess the electronic structure of the 5d valence band for Pt catalyst materials. To extend this work further, the goal is to apply this new technique to additional catalyst materials, such as Pt alloys or single site Pt supported on CeOx, in order to measure the effect of different adsorbates on the electronic structure of the Pt catalyst. This will help derive fundamental insights to drive the development of the next generation of stable dehydrogenation catalyst materials.  </p>

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