Surfactant-free colloidal syntheses of precious metal nanoparticles for improved catalysts

Abstract

Colloidal syntheses of nanomaterials offer multiple benefits to study, understand and optimize un-supported and supported catalysts. In particular, colloidal syntheses are relevant to synthetize (precious) metal nanoparticles. By separating the synthesis of the active phase nanoparticles from supporting steps, a deeper knowledge and a rational control on supported catalyst properties is gained. The effect of nanoparticle size, shape, composition, nature of support or 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, a major drawback is that most colloidal syntheses require the use of additives or surfactants, which are detrimental to most catalytic reactions since they typically block catalyst active sites. Surfactant removal typically adds complexity, can introduce a lack of reproducibility, is energy consuming, generates waste, and prevents the full exploitation of the many benefits of colloidal syntheses for catalysis. Several surfactant-free strategies to obtain stable colloidal nanoparticles are here reviewed. A focus is given to laser synthesis and processing of colloids (LSPC), solution plasma process (SPP), N,N-dimethylformamide (DMF), polyols, and recently reported mono-alcohols based syntheses. The relevance of these synthetic approaches for catalysis is detailed with a focus on heterogeneous catalysis and electro-catalysis.

Influence of Temperature on the Performance of Carbon- and ATO-supported Oxygen Evolution Reaction Catalysts in a Gas Diffusion Electrode Setup

“…1.5 nm in diameter, pristine Ir and Ir x Ru y NPs were synthesized via a surfactant-free, colloidal route using only EtOH as a low-boiling-point solvent. 13,56,57 The NPs were immobilized in a second step on two different commercially available supports, carbon Ketjen Black and ATO, at a nominal metal loading of 50 wt %. The straightforward synthesis approach allows for synthesizing a wide range of different compositions while keeping the particle size constant (see Figure S3).…”

Room Temperature Surfactant-Free Syntheses of Gold Nanoparticles in Alkaline Mixtures of Water and Alcohols: A Model System to Introduce Nanotechnology and Green Chemistry to Future Chemists and Engineers

“…25 For instance, it can be argued that size control can be relatively fine when surfactants are used, however the capping agents prevent in most cases any catalytic activity. 41 In this case, it is more desirable to have relatively poorly defined size control but more activity versus well-defined materials "irrelevant" for catalysis. To add an extra degree of complexity and discussion, it can be stressed that on the contrary, ligands can bring new functionality to the catalyst.…”

“…To add an extra degree of complexity and discussion, it can be stressed that on the contrary, ligands can bring new functionality to the catalyst. 39,41 The green aspects of the synthesis can also be discussed, e.g. use of simple solvents, 3,42 although their high viscosity can be a challenge to further process the nanoparticles.…”

Nanomagnetic tetraaza (N4 donor) macrocyclic Schiff base complex of copper(ii): synthesis, characterizations, and its catalytic application in Click reactions

“…25,26 When one aims at changing the size, spatial organization and electronic conguration, nanocatalysts are alluring alternatives to the conventional catalyst. 25,[27][28][29] Notably, they have a high surface-to-volume ratio and improved catalytic activity, selectivity, and stability. 30,31 The ltration or centrifugation processes used to separate and recover nanocatalysts are difficult and ineffective, which is made worse by the nanoscale size of the catalyst particles, endangering their viability and economics.…”