Ni and Co Based Metal Phosphide Catalysts for Ethane and Propane Dehydrogenation

Current renewable energy production is not able to meet demand. Shale gas is a promising energy source to help bridge the gap between conventional oil and gas and the renewable energy future. Dehydrogenation of light alkanes in the shale gas will play a key role in the utilization of this resource. Current industrial Pt and Cr based dehydrogenation catalysts deactivate, necessitating regular regeneration. Non-noble metal phosphide catalysts have emerged as a promising alternative catalyst because of the ability to tune their geometric and electronic properties by varying composition, their high thermal stability, and because they are not based on noble or highly toxic metals.

A series of Ni and Co based metal phosphides, both supported and unsupported, were synthesized, characterized, and evaluated for ethane and propane dehydrogenation. Both Ni and Co based metal phosphides tested for ethane dehydrogenation demonstrated improved ethylene selectivity over the corresponding pure metal. This is due to the beneficial metal site segregation and charge transfer induced by P. In addition, Co-P was found to have good phase and ethylene production stability when tested for high temperature ethane dehydrogenation (700°C). Due to the inevitable nature of carbon deposition during high temperature dehydrogenation, the impact of oxidative regeneration on the propane dehydrogenation performance of Ni₂P was investigated. While Ni₂P was effectively regenerated using a treatment in air followed by re-reduction, it also partially changed phase from Ni₂P to Ni₁₂P₅ during the propane dehydrogenation and regeneration cycling process. In an effort to improve the phase stability of Ni₂P, it was combined with thermally stable Co-P to form a bimetallic Co_XNi_2-XP material. The bimetallic with a 1:1:1 Co:Ni:P ratio had the high stability of Co₂P and high propylene selectivity, similar to Ni₂P. The results in this dissertation demonstrate the promise that metal phosphides have as alternative dehydrogenation catalysts. Future research investigating other metal phosphide compositions, alkali and alkaline Earth metal doping, and the use of microporous supports has the potential to further enhance the light alkane dehydrogenation performance of metal phosphides.