(655e) Visualizing the Effect of Reaction Parameters and Catalyst Configuration for Tandem Hydrogenation of CO2 to Gasoline-Range Hydrocarbons

Tandem hydrogenation of CO₂ to C₅₊ hydrocarbons is an attractive solution for mitigating CO₂ emissions while producing drop-in replacements for fossil-derived products. This could be achieved by coupling two reactions in the same reactor, which involves the transfer of key reaction intermediates from one system to another. Recent studies show that In₂O₃ combined with HZSM-5 converts CO₂ to gasoline range (C₅₊) hydrocarbons through a two-step process in which CO₂ and H₂ produce methanol over In₂O₃ and then methanol is dehydrated and coupled over HZSM-5 to form hydrocarbons. However, the low conversion and selectivity to C₅₊ hydrocarbons demand a more detailed investigation of the catalytic process to improve hydrocarbon selectivity and catalyst design. Herein, we elucidate how the selection of reaction parameters (temperature, pressure, GHSV) and catalyst configuration can influence the selectivity of hydrogenation products. We demonstrate the optimal reaction conditions required to suppress reverse water gas shift and methanation reaction to increase C₅₊ selectivity. We investigate the effect of the integration manner of In₂O₃ and HZSM-5 on hydrocarbon distribution by changing the spacing of their active sites. We observe that increasing the proximity from the millimeter scale to the micro-scale increases C₅₊ selectivity from 2% to 55%. However, nano-scale proximity yields mostly methane (70%) and no C₅₊ hydrocarbon. Characterization of the fresh and spent catalysts with ammonia TPD reveals that in nano-scale proximity the acidity of HZSM-5 decreases. Hence, we hypothesize that migration of In ion to zeolite driven by the harsh reaction conditions could passivate zeolite in nanoscale proximity. To further investigate, we intentionally passivate HZSM-5 with Na⁺ to evaluate catalytic activity at micro-scale proximity, which yields mostly methane similar to the nano-scale arrangement of In₂O₃ and HZSM-5. To conclude, the selectivity of hydrogenation products can be steered by the selection of reaction parameters and proximity of catalyst components.