Conclusion
Herein we investigated the effect of hydrogen posed over Cr-PNP catalyzed ethylene oligomerization process using DFT calculation. Multiple pathways were tested and compared. The introduction of hydrogen modified the energy barriers during the oligomerization, but the exact effect is debatable and unclear. However, hydrogen do reduce the energy barrier to form the active center on the catalyst, enabling proliferation of active centers. Hence, we propose that hydrogen promotes catalyst activity by easing the formation of active centers on the catalyst.