Recently, a paper of Dr. Wangcheng Zhan, “Surfactant-Assisted Stabilization of Au Colloids on Solids for Heterogeneous Catalysis” has been published on Angewandte Chemie (Angew. Chem. Int. Ed. 2017, 56, 4494-4498). In this work, a novel method was proposed to remove the surfactants on the surface of metal nanoparticle (NPs) and then prepare supported precious metals NPs catalyst with a high thermal stability.

Noble metal nanoparticles (NPs) with controlled size and composition are of great interest for heterogeneous catalysis because of their unique nanostructure-dependent properties. Colloidal noble metal NPs with tunable particle sizes, shapes, and compositions have been extensively used as building blocks to construct supported catalysts. Generally, such NPs can be prepared with nanometer precision using surfactant-assisted approaches. As a result, the resultant ultra-fine NPs is surrounded by surface-bound surfactants or ligands. Although these surfactants can enable the easy dispersion of NPs in the solvent as a stable colloidal solution, organic capping agents present on the NPs surface must be removed to expose active sites when the as-prepared supported NPs are subjected to catalytic reactions. Unfortunately, when these organic layers are removed via solvent extraction or thermal decomposition, the uncapped NPs will be quickly sintered because of the poor interaction between the NPs and supports. Therefore, how to stabilize uncapped colloidal NPs on selected supports is a crucial issue for the development of supported nanocatalysts.

In this work, a simple yet efficient synthetic strategy relying on utilizing the surface-bound surfactants to stabilize Au NPs was developed (Figure above). In this strategy, the as-loaded nanocatalyst is first subjected to annealing under an inert atmosphere, rather than directly treated by washing or oxidation calcination to remove the surfactants to cause sintering. After being subjected to this treatment, the NPs are conformably covered by carbonaceous layers and an enhanced metal–support interaction between the NPs and substrate can be achieved. As a result of those improvements, the Ostwald ripening process was efficiently suppressed during post-thermal treatment in air to remove carbonaceous coatings, thus effectively stabilizing the Au NPs with clean surfaces for heterogeneous catalysis. In contrast, evident sintering of Au NPs was discovered on as-loaded nanocatalyst directly treated by oxidation calcination to remove the surfactants. This method is a general approach that can be widely applied for the stabilization of surfactant-protected NPs, clusters, and even single atoms on a broad range of supports.

The research was completed by Wangcheng Zhan and a continuation of the author’s previous work last year (J. Am. Chem. Soc. 2016, 138, 16130-16139). This work was financially supported by National Key Basic Research Program of China and National Key Research and Development Program of China.