Heterogeneous Oligomerization and Dehydrogenation Catalysis For Shale Gas Valorization

The growing production of shale gas provides increased accessibility to olefin feedstocks, such as ethylene, propylene, and butene, for the manufacturing of plasticizers, lubricants, polymers, precursors to petrochemicals, and fuels. Industrially, the light olefins for oligomerization reactions are produced through catalytic or thermal cracking of saturated hydrocarbons, or direct catalytic dehydrogenation of light alkanes. Depending on the product application, acid-based catalysts and transition metal-based catalysts have been used commercially and studied academically.

This thesis focuses on the synthesis, characterization, testing, and deactivation of Ni- and Zr-based catalysts for olefin oligomerization, as well as Pt-based catalysts for alkane dehydrogenation. Ni sites supported on the defect sites of the Wells–Dawson-type polyoxometalates (Ni-POM-WD) have comparable activation energies during propylene oligomerization to Ni sites in zeolitic materials. Ni-POM-WD has exceptional selectivity toward linear propylene dimers and exhibits significant stability against the impurities that can be present in the shale gas upgrading processes. We further study the possible deactivation route of Ni-catalysts for a Ni-Beta catalyst by using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technique. During ethylene oligomerization, ethylene can solvate the Ni sites and create mobile Ni-ethylene species. DRIFTS experiments on the Ni-Beta catalyst showed a perturbation of the zeolite framework in the presence of ethylene, thus, indirectly implying the mobility of Ni sites. Next, we investigated Zr as a potential catalyst for ethylene oligomerization. We found that the presence of Brønsted acid sites on the catalyst support is important. The Brønsted acid sites of the support act as a chain termination agent for ethylene oligomerization. When Brønsted acid sites are absent, Zr sites favor undesired ethylene polymerization reactions. Lastly, a PtMn catalyst was studied for high temperature alkane dehydrogenation reactions. PtMn confined in siliceous zeolite showed excellent selectivity for ethylene and improved regenerability during ethane dehydrogenation.