Heterogeneous Catalysts. Группа авторов

bulk and surface, good adsorption of reactants at the surface, fast surface transfer of charge carriers from catalysts to reactants, and suitable CBM and VBM position to provide electron–hole pairs with sufficient redox potentials to catalyze the reactions. Each aspect is affected by one or more properties of the surface and bulk. And these effects are not isolated and may affect one another. Figure 2.6 shows how the properties synergistically affect the reactivity and selectivity of semiconductor catalysts and the significance of facets engineering.

Figure 2.6 Diagram of how the facets engineering affects the selectivity and reactivity of a semiconductor photocatalyst.

2.5 Outlook

Reviewing the published studies of facets engineering, from the faceted crystal synthesis to the investigation of the intrinsic property of the exposed surface and to the overall performance of catalysts in various reactions, it is not difficult to find that the benefits of facets engineering are attributed to crystal anisotropy. Facets engineering itself cannot solve all the issues of catalysts. Although catalytic reactions occur mainly on the surface, there are important inherent bulk properties of the catalysts that play significant roles in concert with the engineered facets to maximize the catalytic performance. Just as in single‐atom catalysis, the substrate has a direct influence on the catalytic atoms. Based on the characteristics of the original catalyst, the morphology control brings more possibilities to the performance of the catalysts.

      Although we have attained a good understanding on the mechanisms of facets engineering, we are still facing many challenges, uncertainties, and uncontrollability, such as surface reconstruction. Surface reconstructions always take place on most crystals as a natural phenomenon to minimize surface energy. In many cases where the active facets are the high surface energy facets composed of a high percentage of unsaturated atoms, they become highly unstable upon the removal of capping agents. It inevitably led to the rearrangement of surface atoms or the formation of surface defects, which would have a profound impact on the catalytic properties of the surface.

      More efforts need to be dedicated to developing new synthesis methods for new active facets and structure to reveal new facets‐dependent properties and the synergy between these properties and to control surface defects and identify the substantial differences between the ideal and real surface. There is no doubt that facets engineering is an important strategy to promote the performance of catalysts and provides a valuable platform for the rational design and fabrication of efficient material system.

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