Zeolites are widely used as crystalline microporous materials in chemical and petrochemical industries. Zeolites containing multivalent transition metal ions have gained the attention due to their distinctive chemical and physical properties. In particular, small-pore Cu-CHA zeolites have demonstrated remarkable catalytic efficiency in industrial DeNOx processes and the partial oxidation of methane to methanol.

The activation of these Cu-based zeolite catalysts involves an autoreduction or self-reduction reaction where a portion of Cu(II) species is spontaneously reduced to Cu(I) species at elevated temperatures under vacuum or inert gas conditions. However, a comprehensive computational investigation into the reaction pathways of autoreduction and the intricate molecular-level mechanisms governing this process is needed.

In a study published in Chemistry – An Asian Journal, a research team led by Assoc. Prof. LIU Chong and Prof. ZHUANG Wei from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences conducted a computational investigation into the detailed mechanism of copper autoreduction in Cu-CHA zeolites.

Researchers systematically explored two primary reduction mechanisms. In Mechanism I, two [CuOH]+ species underwent dehydration to form [Cu-O-Cu]2+, and subsequently the reaction of two [Cu-O-Cu]²⁺ species produced molecular O2. In Mechanism II, the production of O2 occurred via [CuO]+ intermediates with the generation of [CuO]⁺ being the critical step.

Researchers highlighted the importance of the O–O distance in reactive intermediates which is influenced by the spatial positioning of lattice aluminum sites hosting the original Cu(II) species. Also, they found that an optimal O–O distance significantly reduced the energy barrier for O2 production, emphasizing the structural role of the zeolite framework in facilitating the autoreduction process.  

Besides, researchers provided a detailed molecular-level understanding of the copper autoreduction mechanism in Cu-CHA zeolites, and illustrated how the structural configuration of the zeolite framework affects catalytic activity.

The findings of this study provide insights into the rational design and optimization of Cu-based zeolite catalysts, paving the way for their enhanced performance in industrial applications.