Coupling CO2 reduction with ethane aromatization for enhancing catalytic stability of iron-modified ZSM-5

Abstract

The shale gas revolution and the carbon-neutrality goal are motivating the landscape toward the synthesis of value-added chemicals or fuels from underutilized ethane with the assistance of greenhouse gas CO2. Combining ethane aromatization with CO2 reduction offers an opportunity to directly produce liquid products for facile separation, storage, and transportation. In the present work, Fe/ZSM-5 catalysts showed promise in the simultaneous CO2 reduction and ethane aromatization at atmospheric pressure and 873 K. The catalysts were further investigated using X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) measurements under in-situ conditions, indicating that most of Fe species existed in the form of Fe oxides and a portion of Fe was incorporated into the ZSM-5 framework generating Lewis acid sites. Both types of Fe species remained almost unchanged under reaction conditions, contributing to an enhanced aromatization activity of Fe/ZSM-5. The effects of CO2 and steam on the acid sites and in turn aromatization activity were also investigated by transient studies, which exhibited a reversible modification behavior. Moreover, CO2 was identified to be critical to enhance coke resistance and in turn catalyst stability. This work highlights the feasibility of using CO2 to assist the upgrading of abundant ethane from shale gas to aromatics over non-precious Fe-based zeolite catalysts.