Surfactant-Free Colloidal Syntheses of Precious Metal Nanoparticles for Improved Catalysts

Colloidal syntheses of nanomaterials offer multiple benefits to study, understand, and optimize unsupported and supported catalysts. In particular, colloidal syntheses are relevant to the synthesis of (precious) metal nanoparticles. By separating the synthesis of the active phase, i.e., the nanoparticles, from supporting steps, a deeper knowledge and rational control of the properties of supported catalysts is gained. The effect(s) of the size, shape, and composition of the nanoparticle, the nature of the support, or the metal loading on a support can be studied in more systematic ways. The fundamental knowledge gained paves the way for catalyst optimization by tuning the catalyst activity, selectivity, and stability. However, most colloidal syntheses require the use of additives or surfactants, which are detrimental to most catalytic reactions because they typically block catalyst active sites. Surfactant removal is therefore often required, which adds complexity to the synthesis and the analysis of the obtained results. Developing surfactant-free strategies to obtain stable colloidal nanoparticles is therefore a rising field of research that is here reviewed. A focus is given to laser synthesis and processing of colloids-, solution plasma process-, N,N-dimethylformamide-, polyol-, and recently reported monoalcohol-based syntheses. The relevance of these synthetic approaches for catalysis is detailed with a focus on heterogeneous catalysis and electrocatalysis.