Читать книгу Heterogeneous Catalysts - Группа авторов - Страница 20

Crystal facets engineering has become one of the most effective strategies to enhance performance of nanomaterials in many applications, such as heterogeneous catalysis, gas or liquid sensing, photocatalysis, electrocatalysis, fuel cell, solar cell, and lithium‐ion batteries [1–4]. The reactions occurred at the surface or interface of nanomaterials are extremely sensitive to the exposed surface atomic structures and their respective physical and chemical properties. The well‐defined crystal surface has unusual properties compared to the bulk, due to the termination of periodic crystal lattices. The various properties of different facets of a single crystal are attributed to crystal anisotropy. As a consequence, the whole behavior of a faceted nanomaterial would be dramatically affected by the surface, especially when the particle size shrinks to a nanoscale and the surface/bulk atomic ratio can no longer be negligible.

This chapter is mainly focused on faceted single crystals of metals and semiconductors in heterogeneous catalysis. Metal catalysts are mainly used in thermal catalysis and electrocatalysis, such as producing chemicals, petroleum refining, and in fuel cells. Studies of metal catalyst surfaces are comprehensive and began much earlier than that of semiconductors in photo‐related catalysis. In the past two decades, significant progress has been made to synthesize metal nanocrystals in a variety of shapes and enhanced performance [5]. Although the miniaturization of catalysts to single (metal) atom catalysts and metal cluster catalysts have become popular in recent years due to the strong desire to attain 100% atom utilization efficiency especially when using some of the least abundant elements [6, 7], the advantage of facets engineering of metal catalysts continues to be an essential and indispensable tool. For example, in photocatalysis where optical absorption is a bulk property that determines the rate of charge carriers generation, it is desirable to apply facets engineering to the bulk crystals to enhance surface charge transfer efficiencies.

Being the core fundamental of heterogeneous catalysis, the studies of surface reactivities have long been appreciated by the community. However, it is only in the last two decades that the tremendous development in the synthesis and characterization of crystal facets further paved the way for significant achievements of facets engineering in catalytic applications. As such, this chapter briefly introduces the mechanisms of facets engineering, the anisotropic properties of crystal facets, and the effects of facets engineering.