二酸化炭素を有価な燃料・化学物質へ変換する新しい反応経路を開発（New Pathways Could Turn Carbon Dioxide Into Valuable Fuels And Chemicals）

2025-08-04 テキサスA&M大学

＜関連情報＞

• https://stories.tamu.edu/news/2025/08/04/new-pathways-could-turn-carbon-dioxide-into-valuable-fuels-and-chemicals/
• https://www.cell.com/chem-catalysis/abstract/S2667-1093(24)00392-0

金属陽イオン交換は、ゼオライト酸サイトを介して、CO2水素化反応中の炭化水素プール伝播を調節する Metal cation exchange with zeolitic acid sites modulates hydrocarbon pool propagation during CO2 hydrogenation

Fatima Mahnaz ∙ Balaji C. Dharmalingam ∙ Jasan Robey Mangalindan ∙ Jenna Vito ∙ Jithin John Varghese ∙ Manish Shetty
Chem Catalysis  Published:November 13, 2024
DOI:https://doi.org/10.1016/j.checat.2024.101183

Graphical abstract

The bigger picture

The design of effective bifunctional oxide/zeolite catalysts for CO₂ hydrogenation to olefins through a methanol (CH₃OH) intermediate hinges on understanding the interaction of different metal oxides with zeolitic Brønsted acid sites (BASs) and its effect on the hydrocarbon pool (HCP) mechanism associated with the CH₃OH-to-olefin (MTO) conversion. Here, we probed the likelihood of metal oxide migration and their cation exchange with BASs and investigated the influence of ion exchange on HCPs. We integrated different metal oxides (e.g., In₂O₃, ZnZrO_x, and Cr₂O₃) with SAPO-34 (a silicoaluminophosphate) at nanoscale proximity to probe their tendency to exchange with BASs and their influence on HCPs. While ion-exchanged In^δ+ species inhibited HCP propagation and Cr^δ+ did not influence HCPs, Zn^δ+ enhanced hydrogen transfer, increasing paraffin selectivity. Overall, we link the consequences of metal-oxide migration and the exchange of cation with BASs to the HCP mechanism for rational design of next-generation catalysts.

Highlights

• Likelihood of metal oxide migration and their cation exchange with BASs was probed
• Ion exchange of BASs with cations influenced hydrocarbon pool (HCP) propagation
• While In^δ+ inhibited HCP propagation, Zn^δ+ promoted hydrogen transfer in HCP
• Cr₂O₃ did not exchange with BAS due to its better thermal stability

Summary

We demonstrate that the exchange of zeolitic Brønsted acid sites (BASs) with cations from metal oxides plays a pivotal role in the propagation of hydrocarbon pools (HCPs) during CO₂ hydrogenation. We probed the likelihood of In₂O₃, ZnZrO_x, and Cr₂O₃ migration and their cation exchange with BASs of a silicoaluminophosphate, SAPO-34, by integrating them at nanoscale proximity (∼1,400 nm). Analysis with NH₃ temperature-programmed desorption and transmission Fourier transform infrared spectroscopy showed ion exchange of BASs with In^δ+ and Zn^δ+ but not for Cr^δ+. We measured the C₃/C₂ hydrocarbon ratio (indicating relative propagation of olefin to aromatic cycles) and paraffin-to-olefin ratio, which revealed that In^δ+ species inhibited HCPs inside the channels of SAPO-34, while Zn^δ+ species enhanced hydrogen transfer and secondary hydrogenation. Combining reactivity data with occluded hydrocarbon analysis and ¹³C solid-state nuclear magnetic resonance spectroscopy, we show that ion-exchanged species affect HCP propagation. Overall, our work provides insights for the rational integration of bifunctional catalysts.