(619e) Uncovering the Deactivation Mechanism of Platinum Catalysts in Light Alkane Dehydrogenation

Catalytic dehydrogenation of light alkanes has been investigated extensively as an attractive alternative other than petroleum cracking to produce alkenes, which are widely used as building blocks for the production of chemicals and polymers. The principal byproduct of hydrogen is also a vital commodity in both petrochemical manufacture and clean energy research. Platinum is known as active catalyst for the reaction but in its pure form suffers from rapid coke deposition, which can lead to changes in product distribution and, more importantly, to catalyst deactivation. The addition of a second metal, such as tin, indium, and gallium, to platinum has been found effective to help suppress the coke formation and in the meantime enhance the product selectivity. However, relatively little is known in understanding the processes by which carbon deposits on platinum surface and in revealing the key factors by which catalyst deactivation is determined.

This talk will present the results of an investigation of the deactivation of platinum catalysts during light alkane dehydrogenation. Both ex situ and in situ high-resolution transmission electron microscopy (HRTEM) investigations were performed in conjunction with measurements of the catalytic performance of ethane dehydrogenation using model platinum catalysts of varied composition and size. The findings suggest that the formation of graphene layers initiates at steps on the surface of the platinum nanoparticles and then grows away from the steps. Both the form and the rate of carbon deposition exhibit strong dependencies on composition and size of the particles, which is attributed to the accommodation of strain energy generated in the graphene layers and the minimization of overall free energy in the growth process. The deactivation mechanism of platinum catalysts as well as the determining factors will be discussed.