Abstract

Alkane coupling with CO2 by metal-containing zeolites catalysis is found to be a promising way to produce aromatics and syngas in recent years, but the real active sites and the role of CO2 are still unclear owing to the quick evolution of the metallic active sites and the complex reaction processes including direct propane aromatization, CO2 hydrogenation, reverse water-gas shift reaction, and propane-CO2 coupling aromatization. Herein, Ga/ZSM-5 catalysts were constructd to study the dynamic evolution of the metallic active sites and the role of CO2 during the propane and CO2 coupling reaction. After optimizing the reaction conditions, a notable propane conversion rate of 97.9% and an impressive aromatics selectivity of 80.6% in hydrocarbons can be achieved at the conditions of 550 °C and CO2/C3H8 of 4. 13CO2 isotope experiments illustrate that C-atoms of CO2 can enter into CO (86.5%) and aromatics (10.8%) during the propane-CO2 coupling reaction process. In situ XANES and FTIR spectroscopies at 550 °C and H2/C3H8 atmosphere reveal that GaOx species can be gradually dispersed into [GaH2]+/[GaH]2+ on the Brønsted acid sites of ZSM-5 zeolite during H2 and/or C3H8 treatment, which are the real active sites for propane-CO2 coupling conversion. In situ CO2-FTIR experiments demonstrate that the [GaH2]+/[GaH]2+ species can react with CO2 and accelerate the propane and CO2 coupling process. This work not only presents a cost-effective avenue for CO2 utilization, but also contributes to the active site design for improved alkane and CO2 activation in coupling reaction system.