Precisely controlled Pd nanoclusters confined in porous organic cages for size-dependent catalytic hydrogenation

Abstract

The precise size-controlled formation of palladium (Pd) nanoclusters with size-dependent catalytic activity was achieved through a cage confinement strategy. In this process, three typical porous organic cages (POCs) with gradually decreasing cavity diameters were used as encapsulation carriers. A series of Pd nanoclusters-based catalysts with corresponding Pd cluster sizes of 0.73, 0.68, and 0.43 nm, respectively, was effectively fabricated by confining the Pd nanoclusters in size-adjustable cavities. The obtained Pd@POCs nanocatalysts exhibited excellent crystallinity, high stability, fascinating morphological characteristics, and superior catalytic hydrogenation performance. Especially, the size-dependent catalytic performance toward hydrogenation of 4-nitrophenol and semi-hydrogenation of alkyne compounds was demonstrated by experimental results and theoretical calculations. The prepared Pd(1.71%)@FT-RCC3 catalyst with the smallest Pd cluster size of about 0.43 nm showed the best catalytic performance. This study promotes a better understanding of size-dependent catalysis and provides a new strategy for the fabrication of customized nanocatalysts.