Metal nanocrystal catalysts (abr. metal nanocatalysts) are widely used in chemical and energy industries. The rare and precious metals as platinum are actually irreplaceable materials for catalysts, therefore to improve the activity and utilization efficiency of metal catalysts is always a challenge. Shape-control synthesis is an efficient way to tailor the surface structure of metal nanocrystal and therefore create particular functions in catalysis. The functional molecules such as stabilizers, capping agents, surfactants and additives, etc., are indispensable in the shape-control synthesis, especially in the wet chemistry route. In order to rationally design and synthesize metal nanocatalysts with high activity, high selectivity and high stability, it is important to explicit the roles and mechanisms of functional agents in shape-control synthesis. The functional agents usually assist in shape-control synthesis of nanocrystals through preferential adsorption on specific crystal facets, or etching particular crystal planes, or accelerating/inhibiting certain crystal growth directions. Although a mass body of metal nanocrystals with different shape have been synthesized, the explicit roles and mechanism of functional molecules in the shape-control synthesis are poorly defined and a full understanding is still elusive. The current paper reviews mainly the recent progress made in studies of mechanism of functional molecules in shape-control synthesis of metal nanocatalysts in the last two decades. The mechanism of preferential adsorption of functional agents and some basic strategy of optimizing the use of functional molecules in shape control synthesis of noble metal nanocatalysts are summarized.

Contents
1 Introduction
2 Shape-control synthesis of noble metal nanocrystal catalysts
2.1 Shape-control synthesis by electrochemical method
2.2 Shape-control synthesis by wet chemistry route
3 The role of functional molecules
3.1 Small molecules
3.2 Etching agents
3.3 Surfactants
3.4 Polymers
3.5 Biomolecules
4 Strategy of using functional molecules in shape-control synthesis of metal nanocatalysts
5 Conclusion and outlook