Kinetic diffusion–controlled synthesis of twinned intermetallic nanocrystals for CO-resistant catalysis

Abstract

Intermetallic catalysts are of immense interest, but how heterometals diffuse and related interface structure remain unclear when there exists a strong metal-support interaction. Here, we developed a kinetic diffusion–controlled method and synthesized intermetallic Pt 2 Mo nanocrystals with twin boundaries on mesoporous carbon (Pt 2 Mo/C). The formation of small-sized twinned intermetallic nanocrystals is associated with the strong Mo-C interaction–induced slow Mo diffusion and the heterogeneity of alloying, which is revealed by an in situ aberration-corrected transmission electron microscope (TEM) at high temperature. The twinned Pt 2 Mo/C constitutes a promising CO-resistant catalyst for highly selective hydrogenation of nitroarenes. Theoretical calculations and environmental TEM suggest that the weakened CO adsorption over Pt sites of Pt 2 Mo twin boundaries and their local region endows them with high CO resistance, selectivity, and reusability. The present strategy paves the way for tailoring the interface structure of high–melting point Mo/W-based intermetallic nanocrystals that proved to be important for the industrially viable reactions.

Atomic-Scale Evidence of Catalyst Evolution for the Structure-Controlled Growth of Single-Walled Carbon Nanotubes

“…Therefore, the rational selection of the metal and support is important for controlling the structure of intermetallic nanocrystals. For example, we employed the SMSI to control the diffusion of metals to synthesize intermetallic Pt 2 Mo nanocrystals with controlled twin boundaries . With the aid of in situ HAADF-STEM, we found that the strong Mo–C interaction led to the sluggish migration of Mo into the Pt nucleus, thereby resulting in the uneven growth of Pt 2 Mo with twin boundaries.…”

“…For example, we employed the SMSI to control the diffusion of metals to synthesize intermetallic Pt 2 Mo nanocrystals with controlled twin boundaries. 54 With the aid of in situ HAADF-STEM, we found that the strong Mo−C interaction led to the sluggish migration of Mo into the Pt nucleus, thereby resulting in the uneven growth of Pt 2 Mo with twin boundaries. The weak Mo−MgO interaction and the template effect of the MgO lattice led to the fast coalescence of Pt 2 Mo along the MgO lattice to form single crystals.…”

Growth modes of single-walled carbon nanotubes on catalysts

“…The relation between catalyst structure and performance plays a critical role in heterogeneous catalysis. The active sites of nanocatalysts have been extensively suggested to be the origin of high selectivity of small molecules (1)(2)(3)(4)(5). The chiral structures of the much larger single-walled carbon nanotube (SWCNT) molecules are more complicated, and two chiral indices (n,m) are required to identify them (6).…”

Unveiling the nucleation and evolution of twinned intermetallic nanocrystals for CO-tolerant selective hydrogenation

“…Our previous work using in situ TEM combined with theoretical calculations demonstrated that the local regions around the Pt 2 Mo twin boundary weaken the CO adsorption and act as active sites for hydrogenation. 47 For CO adsorption on the twinned Pt 2 Mo, the decreased overlap between Pt 5d and CO 2p near the Fermi level resulted in a weak interaction between Pt and CO. The difference in the selective hydrogenation performance of the three kinds of Pt 2 Mo/C catalysts (2, 10, 25 °C min −1 ) under the CO environment can be ascribed to the difference in the content of twinned Pt 2 Mo nanocrystals.…”