Shape-controlled metal nanocrystals for catalytic applications
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troduction Heterogeneous catalysts based on metal nanoparticles are invaluable to the production of many industrially important chemicals and pharmaceuticals1 and as protection for the environment, as exemplified by catalytic converters.2 Despite many decades of development and refinement, most industrial catalysts still employ nanoparticles with broad size distributions and poorly defined shapes. By replacing these nanoparticles with uniform, shape-controlled nanocrystals, it is possible to markedly enhance the performance of many catalytic systems in terms of activity, selectivity, and stability.3 Computational simulations and experimental studies involving bulk single-crystal substrates have long established that the activity and selectivity of a heterogeneous catalyst, for a structure-sensitive reaction, can both be enhanced by controlling the arrangement of atoms on the surface. For example, it has been demonstrated that bulk substrates of Pt can selectively catalyze different types of chemical reactions depending on the surface structure, with the {100} and {210} facets being most active for reactions involving
H2 and CO, respectively (see the following section).4,5 Similar dependences have also been observed for many other different combinations of metals and reactions.6 These examples clearly demonstrate the promise of shape control in maximizing the cost effectiveness and achieving sustainable use of many rare metals. The essence of these studies, however, could not be realized until very recently when it became possible to synthesize metal nanocrystals with controlled shapes, and thus well-defined facets on the surface.7 Thanks to recent advances in shape-controlled synthesis, now is an exciting and rewarding time to rationally design the next generation of catalysts with unparalleled performance for a myriad of reactions by integrating our synthetic capability with a mechanistic understanding of the reaction chemistry. In this article, we discuss the impact of shape-controlled metal nanocrystals on catalysis, together with a brief summary of the solutionbased methods developed for their synthesis. We highlight the practical benefits of these materials in the context of practical reactions, such as the oxygen reduction and formic acid oxidation.
Aleksey Ruditskiy, Georgia Institute of Technology, USA; [email protected] Sang-Il Choi, Georgia Institute of Technology, USA; [email protected] Hsin-Chieh Peng, Georgia Institute of Technology, USA; [email protected] Younan Xia, Georgia Institute of Technology, USA; [email protected] DOI: 10.1557/mrs.2014.167
© 2014 Materials Research Society
MRS BULLETIN • VOLUME 39 • AUGUST 2014 • www.mrs.org/bulletin
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SHAPE-CONTROLLED METAL NANOCRYSTALS FOR CATALYTIC APPLICATIONS
Shape control and its importance in heterogeneous catalysis At a fundamental level, shape control allows us to maneuver the types and proportions of facets that encase the surface of a nanocrystal. These crystallographic facets, each characterized by a specific geometric arran
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