Structure Sensitivity Study of Propane Dehydrogenation on Cobalt Catalysts: HCP versus FCC

In heterogeneous catalysis, it is crucial to understand the structure sensitivity in order to elucidate the reaction mechanism and rationally design optimal catalysts. In this work, propane dehydrogenation (PDH) and side reactions (cracking and deep dehydrogenation) were studied by density functional theory calculations on Co catalysts with different crystallographic structures: face-centered cubic (FCC) and hexagonal closed packed (HCP). Wulff construction reveals that the most stable facet of each crystallographic structure, viz. Co(111) and Co(0001), cover 76.2% and 19.4% of the exposed surface. Various reaction pathways for PDH, deep dehydrogenation, and cracking were explored on Co(111) and Co(0001). Microkinetic simulation results suggest that PDH proceeds through both dehydrogenation pathways (via 1-propyl or 2-propyl intermediate) on Co(111), while it favors path A (via 1-propyl intermediate) on Co(0001). At typical reaction conditions of PDH, Co(111) is more active than Co(0001) by 1.3 times, while the latter is more selective toward propylene production and more resistive to coke formation. Compared to Pt(111), both Co surfaces are more active for PDH while Co(0001) is also more selective toward propylene formation. This work provides fundamental insights into the crystallographic structure sensitivity of propane dehydrogenation on a Co catalyst and useful guidance to achieve better catalytic performance for a Co catalyst.