General Strategy for Preparation of Carbon-Nanotube-Supported Nanocatalysts with Hollow Cavities and Mesoporous Shells

Abstract

Hollow-structured mesoporous catalysts (HMCs) that comprise catalytically active cores, interior reaction space, and permeable shell(s), can bring new opportunities for high-efficiency catalysis. Nevertheless, all the existing HMCs are limited to small spherical yolk–shell type configuration (i.e., zero-dimensional (0D) structure). To include more active cores and to add new merits to the HMCs, in this work, we report a general strategy for preparation of complex one-dimensional (1D) HMCs, in which carbon nanotubes (CNTs) serve as a backbone to support catalytic components and mesoporous silica and/or microporous metal–organic frameworks (MOFs; e.g., ZIF-8) or transition-metal oxides (e.g., Nb2O5) act as membrane-like shells for molecular screening, catalyst protection, and surface functionality. Several types of catalytic nanoparticles (e.g., noble metals Au, Pd, and Au–Pd alloy; and transition metal oxides Co3O4, ZnO, and TiO2) have been anchored onto the CNTs and encapsulated or sheathed with the mesoporous silica shell. Concerning their workability, we have further tested the CNT-based HMCs for selective oxidation of benzyl alcohol to benzaldehyde. Intriguingly, both shell porosity and interior space of catalysts exert significant impacts on benzyl alcohol conversion, benzaldehyde selectivity, and the catalyst longevity. Conceptually, such 1D HMCs can be viewed as linearly integrated 0D HMCs, but they can significantly include more catalytic nanoparticles and enhance catalyst–support interaction, which adds another dimension for the design and synthesis of HMCs.