Investigating the temperature-dependent selectivity of CO2 reduction on Ru-cluster catalysts supported by MXene

The catalytic conversion of carbon dioxide (CO 2 ) into valuable products represents a promising strategy for mitigating the greenhouse effect. However, developing catalysts that exhibit both high activity and selectivity remains a considerable challenge. Composite catalysts based on metal clusters supported on MXene have emerged as a promising candidate for CO 2 reduction. A thorough understanding of the catalytic mechanisms of CO 2 reduction utilizing MXene-based catalysts is crucial for advancing and optimizing these catalysts. In this study, the detailed reaction mechanism of CO 2 reduction on composite Ru n @Mo 2 TiC 2 O 2 catalysts was investigated theoretically, employing the four-atom Ru 4 cluster as the model system. Electronic structure analysis revealed that the orbital interactions between the Ru 4 cluster and CO 2 play a pivotal role in determining the adsorption configuration of the CO 2 molecule. Specifically, CO 2 exhibits distinct adsorption modes on planar and tetrahedral Ru 4 clusters, leading to divergent CO 2 reduction pathways. Density functional theory (DFT) calculations suggest that the tetrahedral Ru 4 cluster demonstrates higher selectivity for the reduction of CO 2 to carbon monoxide (CO) compared to the planar configuration. However, the results indicate that although the planar Ru 4 cluster is predominant on the Mo 2 TiC 2 O 2 surface at room temperature, there is a coexistence of planar and tetrahedral Ru 4 clusters at the higher temperature used in photothermal catalysis. It suggests that the configuration of Ru 4 @Mo 2 TiC 2 O 2 can be modulated by manipulating the reaction temperature, thereby adjusting the selectivity. This finding provides comprehensive insights into the CO 2 reduction mechanism facilitated by MXene-supported metal cluster catalysts. This work also highlights that the impact of temperature on the catalytic activity and selectivity of catalysts comprising metal clusters should be subjected to more rigorous investigation. • CO 2 shows different adsorption behaviors and modes on planar and tetrahedral Ru 4 cluster, leading tovaried selectivities for CO 2 reduction. • The Ru 4 @Mo 2 TiC 2 O 2 structure can be adjusted by changing reaction temperature, thus tuning catalytic selectivity. This offers a new way to control selectivity. • The study highlights the importance of orbital interactions between Ru 4 clusters and the adsorbates CO 2 and H 2 in determining their adsorption modes and the catalytic pathways. • The presence of oxygen vacancies in the Ru 4 @Mo 2 TiC 2 O 2 catalyst does not enhance CO 2 adsorption, due to strong Ru-Mo interactions that obscure the vacancies.