Coupling Conversion of CO2 and n-Butane Over Modified ZSM-5: Incorporation of the Carbon from CO2 into Hydrocarbon Products

The coupling reaction of CO2 and n-butane was conducted over different metal-modified (Mn, Zr, Ni, Ti, Zn) ZSM-5 catalysts. A high CO2 conversion of 26.5% and n-butane conversion of 100% with the aromatics selectivity of 69.1% was achieved at a CO2 to n-butane ratio of 0.95 over Zn/ZSM-5. CO2 addition promoted BTX & olefin selectivity, while it inhibited alkane & A9+ formation. A detailed analysis showed that 13% of the carbon atoms from CO2 were incorporated in the generation of aromatic hydrocarbons. Oxygenated intermediates, such as aliphatic alcohol, aliphatic ketones, and substituted cyclopentenones, were detected sequentially with the increase of the reaction temperature. In addition, reverse Boudouard reaction, water gas shift reaction, and dry reforming also participated in the formation of CO over Zn/ZSM-5. Based on these findings and the detailed characterization results, a plausible mechanism of direct and indirect incorporation of carbon from CO2 into aromatics was proposed for the coupling reaction.