Solutions for catalysis: A surfactant-free synthesis of precious metal nanoparticle colloids in mono-alcohols for catalysts with enhanced performances

To optimize precious metal nanocatalysts, an optimal set of nanoparticle (NP) properties (composition, size, loading, etc.) must match specific operating conditions. Synthesis routes offering independent control on NP properties are then highly desired: (1) to study which combinations of properties are key for an application, (2) to optimize performances, (3) to develop industrial applications if the production method is scalable.

Independent control on heterogeneous catalysts' properties is challenging with the direct formation of NPs on supports: agglomeration and NP formation in pores lead to underutilization of the precious metal under catalytic operation.Our strategy is to use colloids to optimise independently several physical properties of the NPs.Yet in colloidal productions, surfactants are typically required and need to be removed in energy and time consuming steps, resulting in loss of catalytic performances due to sintering and poisoning.

A surfactant-free colloidal synthesis adressing the previous challenges is presented. Pt NPs are obtained at low temperature (< 80 C) in alkaline mono-alcohols. The method is robust, reproducible, promisingly scalable and flexible (e.g. using microwaves, hot water bath, UV irradiation, flow systems).

The mono-alcohol synthesis shows multiple benefits over alternative routes. It is interestingly sensitive to parameters screened in other approaches. The influence of solvents, time of synthesis and nature of base to achieve NP size in the range 1-6 nm and colloidal stability over several months, including in aqueous media, are detailed.

The NPs are characterized by TEM, STEM, FTIR, SAXS, PDF, XAS, and electrochemical methods. The energy, time and cost effective production of NPs in low boiling point solvents leads to improved catalytic performances compared to industrial benchmark for chemical production (butanone hydrogenation) and energy conversion (oxygen reduction).