Direct CO2 Hydrogenation into Liquid Fuels and Chemicals with High Selectivity

As an economical, nontoxic, renewable and abundant carbon source, chemical utilization of CO₂ to value-added products is very attractive because it can not only alleviate the global warming caused by increasing atmospheric CO₂ concentration, but also offer a solution to replace dwindling fossil fuels. Thus, much attention has been paid to the CO₂ conversion to various C1 feedstock. Due to the extreme inertness of CO₂ and a high C–C coupling barrier, it is still a great challenge to synthesize C₂₊ products directly from CO₂, such as olefins, gasoline and aromatics.

We have developed a bifunctional catalyst contained partially reducible metal oxides (In₂O₃) and HZSM-5, which exhibited excellent performance for the direct production of C₅~C₁₁ hydrocarbons from CO₂ hydrogenation with high selectivity. The C₅₊ (hydrocarbons with five or more carbons) selectivity in hydrocarbons distribution reached up to 78.6% with only 1% for CH₄ selectivity at a CO₂ conversion of 13.1%. There was no obvious catalyst deactivation over 150 h, and much better performance for CO₂ hydrogenation to C₅₊ hydrocarbons was observed using pellet catalyst with internal gas recycling. Such results thus suggest a promising potential for its industrial application.

With the above oxide/zeolite bifunctional catalyst for CO₂ hydrogenation to hydrocarbons, the hydrocarbon distribution can be easily tuned through the shape selectivity of the zeolite. When SAPO-34 was chosen as the active phase for C−C coupling, the selectivity to lower olefins reached 80% in hydrocarbons with only 4% of CH₄ at more than 35% CO₂ conversion.

We also fabricated a highly efficient multifunctional catalyst composed of a spinel structural oxide with hierarchical nanocrystalline HZSM-5 zeolites for selective transformation of CO₂ into aromatics. This catalyst displays high aromatic yield (>18%) with high CO₂ conversion (~35%), and the total selectivity of CH₄ and CO has been successfully suppressed to less 20%.