Carbon Dioxide as a Hydrogen-Transport Modulator─Disrupting Surface Hydrogen Accumulation during Propane Aromatization

Introducing CO2 into propane (C3H8) aromatization presents a significant strategy for producing benzene, toluene, and xylene (BTX) while mitigating carbon emissions. This study demonstrates the dual role of CO2 as a hydrogen-transport modulator and carbon contributor in the propane-coupled CO2 aromatization (PCA) process. The Ga/M-Z5 catalyst, with Ga-rich outer layers for CO2 activation and Al-rich channel intersections for aromatization, was achieved through alkali treatment of the support and subsequent chemical liquid deposition (CLD) of the active phase. This catalyst yielded a 54% CO2 conversion and 63% BTX selectivity. The improved BTX selectivity stems from the efficient capture of hydrogen (H*) by CO2. Mechanistic investigations, including kinetic analyses, in situ Fourier transform infrared (FTIR), mass spectrometry, and density functional theory (DFT) calculations, revealed that H* spontaneously transfers from Brønsted acid sites (BAS) to Ga–O bonds. CO2 facilitates the extraction of H* through a pentagonal Ga–O intermediate, thereby suppressing hydrogen-induced side reactions. The high CO2 conversion indicates that CO2 participates in additional pathways beyond reverse water gas shift (RWGS) and reverse Boudouard reactions. Specifically, partial CO2 interacts with oxygen-containing intermediate species, directly contributing to the reconstruction of carbon chains and the formation of aromatic products. These findings provide insights for optimizing catalyst design in PCA systems.