Isolated single atomic site catalysts have attracted great interest due to their remarkable catalytic properties. Because of their high surface energy, single atoms are highly mobile and tend to form aggregate during synthetic and catalytic processes. Therefore, it is a significant challenge to fabricate isolated single atomic site catalysts with good stability. Herein, a gentle method to stabilize single atomic site metal by constructing defects on the surface of supports is presented. As a proof of concept, single atomic site Au supported on defective TiO nanosheets is prepared and it is discovered that (1) the surface defects on TiO nanosheets can effectively stabilize Au single atomic sites through forming the Ti-Au-Ti structure; and (2) the Ti-Au-Ti structure can also promote the catalytic properties through reducing the energy barrier and relieving the competitive adsorption on isolated Au atomic sites. It is believed that this work paves a way to design stable and active single atomic site catalysts on oxide supports.
The electrocatalytic activity of transition-metal-based compounds is strongly related to the spin states. However, the underlying relationship connecting spin to catalytic activity remains unclear. Herein, we carried out density functional theory calculations on oxygen reduction reaction (ORR) catalyzed by Fe single-atom supported on C2N (C2N–Fe) to shed light on this relationship. It is found that the change of electronic spin moments of Fe and O2 due to molecular-catalyst adsorption scales with the amount of electron transfer from Fe to O2, which promotes the catalytic activity of C2N–Fe for driving ORR. The nearly linear relationship between the catalytic activity and spin moment variation suggests electronic spin moment as a promising catalytic descriptor for Fe single-atom based catalysts. Following the revealed relationship, the ORR barrier on C2N–Fe was tuned to be as low as 0.10 eV through judicious manipulation of spin states. These findings thus provide important insights into the relationship between catalytic activity and spin, leading to new strategies for designing transition metal single-atom catalysts.
Dual-metal-site catalysts (DMSCs) have emerged as a frontier in heterogeneous catalysis, while the underlying relationships connecting their dual-site synergistic effects on catalytic performance remain unclear. Here we present a comprehensive first-principles study of O2 activation and CO oxidation on a series of N-coordinated DMSCs. We discovered that the N3-coordinated-adjacent dual-metal model has stronger synergistic and dynamic effects, leading to much higher catalytic activity than others investigated. Based on this model, detailed comparisons of various metal combinations (M = Fe, Co, Ni, Cu, and Pt) show that Fe-containing combinations are generally more active than others. In particular, the Fe–Ni combination, owing to its preferential coadsorption of CO+O2 and highest activity is identified as the most promising candidate for CO oxidation. To explore some universal descriptors for catalytic performance of different combinations, various relationships (50 in total) were systemically studied. It is found that the designed electronic/spectral descriptors of charge transfer, average charge on metals, average d-orbital center on metals, and stretching vibrational frequency of reactants may reflect the binding ability/stability of O2 as lone reactant. However, for multiple reactants (CO+O2), the binding stability/reactivity of the key-species (O2) descriptor has better performance. The transferability of such descriptors to multimolecular catalysis was confirmed by applying them to NO oxidation. These novel descriptors highlight the importance of structure–activity relationships under reaction conditions, thus providing potential design strategies for high-efficiency DMSCs.
Polarized charges on dual-reactive centers of C2N-supported single-atom based transition metal ion catalysts promoting HCOOH dehydrogenation.
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