Synthetic architecture of integrated nanocatalysts with controlled spatial distribution of metal nanoparticles

Abstract

Integrated nanocatalysts (INCs) with high compositional and structural complexities are recognized as a new class of heterogeneous catalysts exhibiting more advantageous features than the conventional ones. In this work, we have developed a general synthetic protocol for the design and fabrication of INCs by controllable integration of hollow or non-hollow Cu2O, noble metal nanoparticles (MNPs, M = Au, Pd, and Pt) and mesoporous silica (mSiO2) into a single and well-defined matrix. The synthetic protocol was based on stepwise fabrication manner involving sol-gel process to coat mesoporous silica, Ostwald ripening process to generate void space, and galvanic replacement process to deposit ultrafine catalytic MNPs. As a demonstration, in total, our method gives rise to 14 different kinds of INCs with two to four components, such as Cu2O@M, Au@Cu2O@M, Au@hCu2O@M, and Au@hCu2O@M@mSiO2, etc. Interestingly, INCs with the various spatial distributions of MNPs on mSiO2 were constructed by using Cu2O as a sacrificial template under deliberately controlled pH condition. For instance, location regulation of MNPs was achieved on the external surface of mSiO2 wall or inside the mSiO2 cavity due to the different redox couple of metal precursors and different dissolution rate of Cu2O during the galvanic replacement process. The workability of the designed INCs was also examined with 4-nitrophenol reduction in the liquid phase and the enhanced catalytic activity was found with catalysts having more exposed MNPs on the external silica surface.