Metal nanocrystals with controlled shapes or surface structures have received increasing attention, owing to their desirable properties for applications ranging from catalysis to photonics, energy and biomedicine. Most studies, however, have been limited to nanocrystals with the same crystal phase as the bulk material. Engineering the phase of metal nanocrystals while simultaneously attaining shape-controlled synthesis has recently emerged as a new frontier of research. Here, we use Ru as an example to evaluate recent progress in the synthesis of metal nanocrystals featuring different crystal phases and well-controlled shapes. We first discuss synthetic strategies for controlling the crystal phase and shape of Ru nanocrystals, with a focus on new mechanistic insights. We then highlight the major factors that affect the packing of Ru atoms and, thus, the crystal phase, followed by an examination of the thermal stability of Ru nanocrystals in terms of both crystal phase and shape. Next, we showcase the successful implementation of these Ru nanocrystals in various catalytic applications. Finally, we end with a discussion of the challenges and opportunities in the field, including leveraging the lessons learned from Ru to engineer the crystal phase and surface structure of other metals.

具有受控形状或表面结构的金属纳米晶体由于其在从催化到光子学，能量和生物医学等应用中的理想性能而受到越来越多的关注。然而，大多数研究仅限于具有与块状材料相同的晶相的纳米晶体。最近，工程化金属纳米晶体的相并同时实现形状控制的合成已成为研究的新领域。在这里，我们以Ru为例，评估具有不同晶相和形状受控的金属纳米晶体的合成进展。我们首先讨论控制Ru纳米晶体的晶体相和形状的合成策略，重点是新的机理见解。然后，我们重点介绍影响Ru原子堆积的主要因素，因此，观察到了晶相，然后从晶相和形状两方面检查了Ru纳米晶体的热稳定性。接下来，我们展示了这些Ru纳米晶体在各种催化应用中的成功实施。最后，我们最后讨论了该领域的挑战和机遇，包括利用从Ru汲取的教训来设计其他金属的晶体相和表面结构。