ZSM-5
zeolite modified by zinc is a promising catalyst for light
alkane aromatization. CO2-assisted oxidative dehydrogenation
and aromatization of propane can be achieved over Zn/ZSM-5, but the
aromatization pathways and the role of CO2 remain to be
clarified. With density functional theory calculations, this work
investigates the reaction networks and key steps in propane aromatization
over Zn/ZSM-5, the promotional role of CO2 in the consumption
of H2 and the removal of carbon deposits, as well as the
rate-limiting steps in the conversion of propane to aromatics. The
calculation results demonstrate that Zn-Lewis acid sites play a vital
role in propane dehydrogenation, while the subsequent propene aromatization
proceeds under the synergetic action of both Brønsted and Zn-Lewis
acid sites. Due to the high barrier step of CO2 activation
involved in the reverse Boudouard reaction over Zn/ZSM-5, we identify
that introducing a second metal component such as Pt or Cu into Zn/ZSM-5
can promote the removal of carbon deposits, thus leading to the enhanced
catalyst stability and more active sites for aromatization.