Читать книгу Heterogeneous Catalysts - Группа авторов - Страница 76

SACs have been studied in catalytic oxidation, water–gas shift (WGS), hydrogenation, and electrocatalysis, showing superior catalytic performance vs. their counterparts (i.e. supported NPs) [15, 16, 24–26]. The high activity of SACs may be ascribed to the unique coordination of SAs with neighboring atoms of the support as well as metal–support interactions. For example, Pt₁/FeO_x SAC showed much higher activity for CO oxidation than Pt NPs supported on FeO_x, owing to the partially vacant 5d orbitals of the positively charged, high‐valent Pt atoms [16]. Yang and coworkers reported the use of M₁/TiO₂ (M = Pt, Pd, Rh, or Ru) in photocatalytic hydrogen evolution and illustrated a 6‐ to 13‐fold increase in photocatalytic activity compared with the metal clusters loaded onto TiO₂ [24]. Furthermore, the active single‐atom sites are well defined, and the identical geometric structure of each active site may result in excellent selectivity compared with the nanoscale counterparts that often have multiple types of active sites. Yan et al. reported that atomically dispersed Pd on graphene showed 100% selectivity to butenes in catalytic hydrogenation of 1,3‐butadiene. In particular, the selectivity to 1‐butene can reach ∼70% at 95% conversion at 50 °C, as explained by the change of 1,3‐butadiene's adsorption mode due to the geometric effect (Figure 6.2) [25]. Anderson and coworkers reported a study of oxygen reduction reaction catalyzed by size‐selected Pt_n clusters deposited on indium tin oxide [26]. The materials showed increased H₂O₂ selectivity as the Pt_n cluster size decreased, and a maximized H₂O₂ selectivity was observed with the smallest Pt₁ species [26].

Figure 6.2 Schematic illustration of improvement of selectivity to butenes on single‐atom Pd₁/graphene catalyst.

Source: Yan et al. 2015 [25]. Reproduced with permission of American Chemical Society.

(See online version for color figure).